Dengue fever

A Review on Dengue fever
A dissertation submitted to the Department of Pharmacy, State
University of Bangladesh in the partial fulfillment of the
requirements for the degree of Bachelor of Pharmacy
Submitted by
Md.Akibur Rahman Akash
Student ID: UG08-32-18-054
Date of submission: September, 2020

Table of content
A Review on Dengue fever Page I
Abstract i
Chapter 01: introduction
1.1 What is it ? 1
1.1.1 Global burden 3
1.1.2 Dengue viruses 11
1.1.3 Transmission 11
1.1.4 Pathogenesis 12
1.2 History 13
1.3 Prognosis 14
1.4 Etymology 15
Chapter 02: Signs and symptom
2.1 Signs and symptom 16
2.2 Clinical course of dengue fever 16
2.3 Clinical course 17
2.4 Associated problems 19
2.5 Cause 20
2.5.1 Virology 20
2.5.2 Transmission 21
2.5.3 Predisposition 22
2.6 Mechanism 22
2.6.1 Viral replication 23
2.6.2 Severe disease 24
Chapter03:Diagnosis
3.1 Diagnosis 26
3.2 Classification 27
3.3 Laboratory tests 27
3.4 Prevention 28

Table of content
A Review on Dengue fever Page II
3.5 Vaccine 31
3.6 Anti-dengue day 32
Chapter 04: Management and treatment
4.1 Management 33
4.2 Treatment 33
4.2.1 Blood donation 34
4.2.2 Awareness efforts 34
4.3 Research 34
4.3.1 Vector 35
4.3.2 Wolbachia 35
4.3.3 Treatment 35
Conclusion 46
Reference 47
|
Figure 2.1: The typical rash seen in dengue fever 2
Figure 2.1: Schematic depiction of the symptoms of dengue fever 16
Figure 2.2: The rash of dengue fever in the acute stage of the
infection blanches when pressed
18
Figure 2.3 The rash that commonly forms during the recovery from dengue fever
with its classic islands of white in a sea of red.
19
Figure 2.4 showing dengue virus e(4the cluster of dark dots near the center) 20
Figure 2.5 The mosquito Aedes aegypti feeding on a human host 21
Figure 2.6: In antibody-dependent enhancement (ADE), antibodies bind to both
viral particles and Fc gamma receptors expressed on immune cells, increasing the
likelihood that the viruses will infect those cells.
24
Figure 3.1 Graph of when laboratory tests for dengue fever become positive. Day
zero refers to the start of symptoms, 1st refers to in those with a primary
infection, and 2nd refers to in those with a secondary infection.[25]
28

Table of content
A Review on Dengue fever Page III
Figure 3.2 A 1920s photograph of efforts to disperse standing water and thus
decrease mosquito populations
30
Figure 3.3 A poster in Tampines, Singapore, notifying people that there are ten or
more cases of dengue in the neighbourhood (November 2015).
32
Figure 4.1 Public health officers releasing P. reticulata fry into an artificial lake in
the Lago Norte district of Brasília, Brazil, as part of a vector control effort
35

Abstract
A Review on Dengue fever Page i
Abstract
Transmitted by Aedes mosquitoes all over the inter-tropical area, Dengue fever is the leading
arboviral disease in humans. It is also an emerging disease. Increasing morbidity-mortality, and
geographical expansion are the drastic changes noted in the recent epidemiology of the disease.
They are related to those occurring at the bio-climatic, socio-demographic and behavioural
levels, which in turn may have led to enhanced viral circulation and virulence, and also vectorial
resistance. The various clinical patterns (undifferentiated febrile episode of children, acute and
algid classic form, the potentially fatal dengue hemorrhagic fever/dengue shock syndrome, and
the atypical forms) are reviewed, as well as the diagnostic methods, and the pathogenesis
(sequential infections, facilitating antibodies, capillary leakage). Dengue fever is actually much
more than a traveller's fever or an exotic curiosity. It presently threatens half the world's
population, and remains a puzzling disease in many aspects, such as the virus-vector and host-
virus relationships, and clinical expression variability. In this respect, dengue fever appears as a
model of viral disease. The current molecular approach is expected to provide us with new
insights into pathophysiology, more efficient tools for disease control, and also an efficient
vaccine in the near future.

Chapter-01: Introduction
A Reviewon Dengue fever Page 1
1.1 What is it ?
Dengue fever is a mosquito-borne tropical disease caused by the dengue virus. Symptoms
typically begin three to fourteen days after infection. These may include a
high fever, headache, vomiting, muscle and joint pains, and a characteristic skin
rash.Recovery generally takes two to seven days. In a small proportion of cases, the disease
develops into severe dengue, also known as dengue hemorrhagic fever, resulting
in bleeding, low levels of blood platelets and blood plasma leakage, or into dengue shock
syndrome, where dangerously low blood pressure occurs.
Dengue is spread by several species of female mosquitoes of the Aedes genus,
principally Aedes aegypti. The virus has five serotypes, infection with one type usually gives
lifelong immunity to that type, but only short-term immunity to the others. Subsequent
infection with a different type increases the risk of severe complications. A number of tests
are available to confirm the diagnosis including detecting antibodies to the virus or its RNA.
A vaccine for dengue fever has been approved and is commercially available in a number of
countries. As of 2018, the vaccine is only recommended in individuals who have been
previously infected, or in populations with a high rate of prior infection by age nine. Other
methods of prevention include reducing mosquito habitat and limiting exposure to bites. This
may be done by getting rid of or covering standing water and wearing clothing that covers
much of the body. Treatment of acute dengue is supportive and includes giving fluid either by
mouth or intravenously for mild or moderate disease. For more severe cases, blood
transfusion may be required. About half a million people require hospital admission every
year. Paracetamol (acetaminophen) is recommended instead of non steroidal anti-
inflammatory drugs (NSAIDs) for fever reduction and pain relief in dengue due to an
increased risk of bleeding from NSAID use.

Figure2.1: Thetypical rash seenin denguefever
It is a common communicable disease characterized by occurrence of high fever, severe body
aches and intense headache. It is a very common disease that occurs in epidemic form from
time to time. Delhi and parts of North India experienced a large number of cases of Dengue
in 1996, 2003 and 2006. The disease is quite severe in young children as compared to adults.
It is a disease which occurs throughout the world except in Europe and affects a large number
of people. For example, it is estimated that every year, 2 crore cases of Dengue fever occur in
the world. Death rate varies from 5 per 100 cases to 30 per 100 cases. ♦ Cause ? It is caused
by a virus (Dengue Virus) which has got four different types (Type 1,2,3,4). Common name
of the disease is ‘break-bone fever’ "(Haddi Tod Bukhar)" because of severe body and joint
pains produced. ♦ Spread Just like in Malaria, Dengue fever is also spread by bites of
mosquitoes. In this case, the mosquitoes are “Aedes” mosquitoes which are very tough and
bold mosquitoes and bite even during day time. This disease occurs more frequently in the
rainy season and immediately afterwards in India. The Dengue virus is present in the blood of
the patient suffering from Dengue fever. Whenever an Aedes mosquito bites a patient of
Dengue fever, it sucks blood and along with it, the Dengue virus into its body. The virus
undergoes further development in the body of the mosquito for a few days. When the virus
containing mosquito bites a normal human being, the virus is injected into the person’s body
and he/she becomes infected and can develop symptoms of Dengue fever. 2 ♦ Incubation
Period : It means the time between bite of an infected mosquito and appearance of symptoms
of dengue fever in the bitten person. Commonly, it is 5-6 days. However it can vary from 3-
10 days

1.1.1 Global burden
Dengue is the most rapidly spreading mosquito-borne viral disease in the world. In the last 50
years, incidence has increased 30-fold with increasing geographic expansion to new countries
and, in the present decade, from urban to rural settings. An estimated 50 million dengue
infections occur annually and approximately 2.5 billion people live in dengue endemic
countries. The 2002 World Health Assembly resolution WHA55.urged greater commitment
to dengue by WHO and its Member States. Of particular signifi cance is the 2005 World
Health Assembly resolution WHA58.3 on the revision of the International Health Regulations
(IHR), which includes dengue as an example of a disease that may constitute a public health
emergency of international concern with implications for health security due to disruption
and rapid epidemic spread beyond national borders. The global prevalence of dengue has
grown dramatically in recent decades. The disease is now endemic in 112 countries of Africa,
the Americas, the Eastern Mediterranean, Southeast Asia and the Western Pacific. WHO
estimates that 40% of the world’s population, about 2.5 billion people living in tropical and
subtropical areas are at risks. Every year about 50-100 million cases of dengue infection,
500,000 cases of DHF and at least 12,000 deaths occur worldwide; ninety percent of these
deaths occur in children less than 15 years of age.1,2 More than 160,000 cases of dengue and
dengue hemorrhagic fever have been reported in the Western Pacific region. In 2005, there
were about 320,000 cases of dengue in the Americas, of which 15,253 cases were DHF; there
were 80 deaths reported. Brazil alone accounted for about two thirds of the cases and half of
the deaths. These figures are higher than those for the year 2004: 267,050 cases of classic
dengue fever and 9,810 cases of DHF, and 71 deaths. In 2001, Brazil reported over 390,000
cases, including more than 670 cases of DHF. During dengue epidemics, attack rates among
susceptible individuals are often 40-50%, but may reach 80-90%. An estimated 500,000 cases
of DHF require hospitalization each year, of which a very large proportion are children. At
least 2.5% of cases die, although case fatality could be twice as high. Without proper
treatment, DHF case fatality rates can exceed 20%. With modern intensive supportive
therapy, such rates can be reduced to less than 1%.
Dengue in Asia and the Pacific.
Some 1.8 billion (more than 70%) of the population at risk for dengue worldwide live in
member states of the WHO South-East Asia Region and Western Pacific Region, which bear
nearly 75% of the current global disease burden due to dengue. The Asia Pacific Dengue
Strategic Plan for both regions (2008--2015) has been prepared in consultation with member

countries and development partners in response to the increasing threat from dengue, which is
spreading to new geographical areas and causing high mortality during the early phase of
outbreaks. The strategic plan aims to aid countries to reverse the rising trend of dengue by
enhancing their preparedness to detect, characterize and contain outbreaks rapidly and to stop
the spread to new areas.
Dengue in the WHO.
South-East Asia Region Since 2000, epidemic dengue has spread to new areas and has
increased in the already affected areas of the region. In 2003, eight countries -- Bangladesh,
India, Indonesia, Maldives, Myanmar, Sri Lanka, Thailand and Timor-Leste -- reported
dengue cases. In 2004, Bhutan reported the country’s first dengue outbreak. In 2005, WHO’s
Global Outbreak Alert and Response Network (GOARN) responded to an outbreak with a
high case-fatality rate (3.55%) in Timor-Leste. In November 2006, Nepal reported indigenous
dengue cases for the first time. The Democratic Peoples’ Republic of Korea is the only
country of the South-East Region that has no reports of indigenous dengue. The countries of
the region have been divided into four distinct climatic zones with different dengue
transmission potential. Epidemic dengue is a major public health problem in Indonesia,
Myanmar, Sri Lanka, Thailand and Timor-Leste which are in the tropical monsoon and
equatorial zone where Aedes aegypti is widespread in both urban and rural areas, where
multiple virus serotypes are circulating, and where dengue is a leading cause of
hospitalization and death in children. Cyclic epidemics are increasing in frequency and in-
country geographic expansion is occurring in Bangladesh, India and Maldives -- countries in
the deciduous dry and wet climatic zone with multiple virus serotypes circulating. Over the
past four years, epidemic dengue activity has spread to Bhutan and Nepal in the sub-
Himalayan foothills. Reported case fatality rates for the region are approximately 1%, but in
India, Indonesia and Myanmar, focal outbreaks away from the urban areas have reported
case-fatality rates of 3--5%. In Indonesia, where more than 35% of the country’s population
lives in urban areas, 150 000 cases were reported in 2007 (the highest on record) with over 25
000 cases reported from both Jakarta and West Java. The case-fatality rate was approximately
1%. In Myanmar in 2007 the states/divisions that reported the highest number of cases were
Ayayarwaddy, Kayin, Magway, Mandalay, Mon, Rakhine, Sagaing, Tanintharyi and Yangon.
From January to September 2007, Myanmar reported 9578 cases. The reported case-fatality
rate in Myanmar is slightly above 1%. In Thailand, dengue is reported from all four regions:
Northern, Central, North-Eastern and Southern. In June 2007, outbreaks were reported from

Trat province, Bangkok, Chiangrai, Phetchabun, Phitsanulok, Khamkaeng Phet, Nakhon
Sawan and Phit Chit. A total of 58 836 cases were reported from January to November 2007.
The case-fatality rate in Thailand is below 0.2%. Dengue prevention and control will be
implemented through the Bi-regional Dengue Strategy (2008--2015) of the WHO South-East
Asia and Western Pacific regions. This consists of six elements: (i) dengue surveillance, (ii)
case management, (iii) outbreak response, (iv) integrated vector management, (v) social
mobilization and communication for dengue and (vi) dengue research (a combination of both
formative and operational research). The strategy has been endorsed by resolution
SEA/RC61/R5 of the WHO Regional Committee for South-East Asia in 2008.
Dengue in the WHO Western Pacific Region
Dengue has emerged as a serious public health problem in the Western Pacific Region. Since
the last major pandemic in 1998, epidemics have recurred in much of the area. Lack of
reporting remains one of the most important challenges in dengue prevention and control.
Between 2001 and 2008, 1 020 333 cases were reported in Cambodia, Malaysia, Philippines,
and Viet Nam -- the four countries in the Western Pacific Region with the highest numbers of
cases and deaths. The combined death toll for these four countries was 4798 (official country
reports). Compared with other countries in the same region, the number of cases and deaths
remained highest in Cambodia and the Philippines in 2008. Overall, case management has
improved in the Western Pacific Region, leading to a decrease in case fatality rates. Dengue
has also spread throughout the Pacific Island countries and areas. Between 2001 and 2008,
the six most affected Pacific island countries and areas were French Polynesia (35 869 cases),
New Caledonia (6836 cases), Cook Islands (3735 cases), American Samoa (1816 cases),
Palau (1108 cases) and the Federal States of Micronesia (664 cases). The total number of
deaths for the six island countries was 34 (official country reports). Although no official
reports have been submitted to WHO by Kiribati, the country did experience a dengue
outbreak in 2008, reporting a total of 837 cases and causing great concern among the national
authorities and among some of the other countries in the region. Historically, dengue has
been reported predominantly among urban and peri-urban populations where high population
density facilitates transmission. However, evidence from recent outbreaks, as seen in
Cambodia in 2007, suggests that they are now occurring in rural areas. Implementing the Bi-
regional Dengue Strategy for Asia and the Pacific (2008--2015) is a priority following
endorsement by the 2008 resolution WPR/RC59.R6 of the WHO Regional Committee for the
Western Pacific.

Dengue in the Americas.
Interruption of dengue transmission in much the WHO Region of the Americas resulted from
the Ae. aegypti eradication campaign in the Americas, mainly during the 1960s and early
1970s. However, vector surveillance and control measures were not sustained and there were
subsequent reinfestations of the mosquito, followed by outbreaks in the Caribbean, and in
Central and South America. Dengue fever has since spread with cyclical outbreaks occuring
every 3--5 years. The biggest outbreak occurred in 2002 with more than 1 million reported
cases. From 2001 to 2007, more than 30 countries of the Americas notified a total of 4 332
731 cases of dengue. The number of cases of dengue haemorhagic fever (DHF) in the same
period was 106 037. The total number of dengue deaths from 2001 to Chapter 1:
Epidemiology, burden of disease and transmission 7 CHAPTER 1 2007 was 1299, with a
DHF case fatality rate of 1.2%. The four serotypes of the dengue virus (DEN-1, DEN-2,
DEN-3 and DEN-4) circulate in the region. In Barbados, Colombia, Dominican Republic, El
Salvador, Guatemala, French Guyana, Mexico, Peru, Puerto Rico and Venezuela, all four
serotypes were simultaneously identified in one year during this period. By subregion of the
Americas, dengue is characterized as described below. All data are from the Pan American
Health Organization (PAHO). The Southern Cone countries Argentina, Brazil, Chile,
Paraguay and Uruguay are located in this subregion. In the period from 2001 to 2007, 64.6%
(2 798 601) of all dengue cases in the Americas were notified in this subregion, of which
6733 were DHF with a total of 500 deaths. Some 98.5% of the cases were notified by Brazil,
which also reports the highest case fatality rate in the subregion. In the subregion, DEN-1, -2
and -3 circulate. Andean countries This subregion includes Bolivia, Colombia, Ecuador, Peru
and Venezuela, and contributed 19% (819 466) of dengue cases in the Americas from 2001 to
2007. It is the subregion with the highest number of reported DHF cases, with 58% of all
cases (61 341) in the Americas, and 306 deaths. Colombia and Venezuela have most cases in
the subregion (81%), and in Colombia there were most dengue deaths (225, or 73%). In
Colombia, Peru and Venezuela all four dengue serotypes were identified. Central American
countries and Mexico During 2001–2007, a total of 545 049 cases, representing 12.5% of
dengue in the Americas, was reported, with 35 746 cases of DHF and 209 deaths. Nicaragua
had 64 deaths (31%), followed by Honduras with 52 (25%) and Mexico with 29 (14%). Costa
Rica, Honduras and Mexico reported the highest number of cases in this period. DEN-1, -2
and -3 were the serotypes most frequently reported. Caribbean countries In this subregion

3.9% (168 819) of the cases of dengue were notified, with 2217 DHF cases and 284 deaths.
Countries with the highest number of dengue cases in the Latin Caribbean were Cuba, Puerto
Rico and the Dominican Republic, whereas in the English and French Caribbean, Martinique,
Trinidad and Tobago and French Guiana reported the highest numbers of cases. The
Dominican Republic reported 77% of deaths during the period 2001--2007. All four
serotypes circulate in the Caribbean area, but predominantly DEN-1 and -2. North American
countries The majority of the notified cases of dengue in Canada and the United States are
persons who had travelled to endemic areas in Asia, the Caribbean, or Central or South
America. From 2001 to 2007, 796 cases of dengue were reported in the United States, the
majority imported. Nevertheless, outbreaks of dengue in Hawaii have been reported, and
there were outbreaks sporadically with local transmission in Texas at the border with Mexico.
Dengue: Guidelines for diagnosis, treatment, prevention and control 8 The Regional Dengue
Programme of PAHO focuses public policies towards a multisectoral and interdisciplinary
integration. This allows the formulation, implementation, monitoring and evaluation of
national programs through the Integrated Management Strategy for Prevention and Control of
Dengue (EGI-dengue, from its acronym in Spanish). This has six key components: (i) social
communication (using Communication for Behavioral Impact (COMBI)), (ii) entomology,
(iii) epidemiology, (iv) laboratory diagnosis, (v) case management and (vi) environment. This
strategy has been endorsed by PAHO resolutions (12–15). Sixteen countries and three
subregions (Central America, Mercosur and the Andean subregion) agreed to use EGI-dengue
as a strategy and are in the process of implementation.
Dengue in the WHO African Region.
Although dengue exists in the WHO African Region, surveillance data are poor. Outbreak
reports exist, although they are not complete, and there is evidence that dengue outbreaks are
increasing in size and frequency. Dengue is not officially reported to WHO by countries in
the region. Dengue-like illness has been recorded in Africa though usually without laboratory
confirmation and could be due to infection with dengue virus or with viruses such as
chikungunya that produce similar clinical symptoms. Dengue has mostly been documented in
Africa from published reports of serosurveys or from diagnosis in travellers returning from
Africa, and dengue cases from countries in Sub-Saharan Africa. A serosurvey suggests that
dengue existed in Africa as far back as 1926--1927, when the disease caused an epidemic in
Durban, South Africa. Cases of dengue imported from India were detected in the 1980s. For

eastern Africa, the available evidence so far indicates that DEN-1, -2 and -3 appear to be
common causes of acute fever. Examples of this are outbreaks in the Comoros in various
years (1948, 1984 and 1993, DEN-1 and -2) and Mozambique (1984--1985, DEN-3). In
western Africa in the 1960s, DEN-1, -2 and -3 were isolated for the first time from samples
taken from humans in Nigeria. Subsequent dengue outbreaks have been reported from
different countries, as for example from Burkina Faso (1982, DEN-2) and Senegal (1999,
DEN-2). Also DEN-2 and DEN-3 cases were confirmed in Côte d’Ivoire in 2006 and 2008.
Despite poor surveillance for dengue in Africa, it is clear that epidemic dengue fever caused
by all four dengue serotypes has increased dramatically since 1980, with most epidemics
occurring in eastern Africa, and to a smaller extent in western Africa, though this situation
may be changing in 2008. While dengue may not appear to be a major public health problem
in Africa compared to the widespread incidence of malaria and HIV/AIDS, the increasing
frequency and severity of dengue epidemics worldwide calls for a better understanding of the
epidemiology of dengue infections with regard to the susceptibility of African populations to
dengue and the interference between dengue and the other major communicable diseases of
the continent. Chapter 1: Epidemiology, burden of disease and transmission 9
Dengue in the WHO Eastern Mediterranean Region.
Outbreaks of dengue have been documented in the Eastern Mediterranean Region possibly as
early as 1799 in Egypt. The frequency of reported outbreaks continue to increase, with
outbreaks for example in Sudan (1985, DEN-1 and -2) and in Djibouti (1991, DEN-2).
Recent outbreaks of suspected dengue have been recorded in Pakistan, Saudi Arabia, Sudan
and Yemen, 2005--2006. In Pakistan, the first confirmed outbreak of DHF occurred in 1994.
A DEN-3 epidemic with DHF was first reported in 2005. Since then, the expansion of dengue
infections with increasing frequency and severity has been reported from large cities in
Pakistan as far north as the North-West Frontier Province in 2008. Dengue is now a
reportable disease in Pakistan. A pertinent issue for this region is the need to better
understand the epidemiological situation of dengue in areas that are endemic for Crimean-
Congo haemorrhagic fever and co-infections of these pathogens. Yemen is also affected by
the increasing frequency and geographic spread of epidemic dengue, and the number of cases
has risen since the major DEN-3 epidemic that occurred in the western al-Hudeidah
governorate in 2005. In 2008 dengue affected the southern province of Shabwa. Since the
first case of DHF died in Jeddah in 1993, Saudi Arabia has reported three major epidemics: a
DEN-2 epidemic in 1994 with 469 cases of dengue, 23 cases of DHF, two cases of dengue

shock syndrome (DSS) and two deaths; a DEN-1 epidemic in 2006 with 1269 cases of
dengue, 27 cases of DHF, 12 cases of DSS and six Figure 1.3 Outbreaks of dengue fever in
the WHO Eastern Mediterranean Region, 1994–2005 DEN-2: 1994: 673 suspected cases, 289
confirmed cases 1995: 136 suspected cases, 6 confirmed cases 1996: 57 suspected cases, 2
confirmed cases 2001: 7 suspected cases, 0 confirmed cases 2005: 32 suspected (confirmed)
Al-Hudaydah, Mukkala, Shaabwa (1994, DEN-3, no data); Al-Hudaydah, Yemen (September
2000, DEN-2, 653 suspected cases, 80 deaths (CFR = 12%)); Al-Hudaydah, Yemen (March
2004, 45 suspected cases, 2 deaths); Al-Hudaydah, Mukkala (March 2005, 403 suspected
cases, 2 deaths); Somalia (1982, 1993, DEN-2) Djibouti (1991-1992, DEN-2) Sudan (No
data) Dengue: Guidelines for diagnosis, treatment, prevention and control 10 deaths; and a
DEN-3 epidemic in 2008 with 775 cases of dengue, nine cases of DHF, four cases of DSS
and four deaths. A pertinent issue for the IHR is that Jeddah is a Haj entry point -- as well as
being the largest commercial port in the country, and the largest city with the busiest airport
in the western region -- with large numbers of people coming from high-burden dengue
countries such as Indonesia, Malaysia and Thailand, in addition to the dengue-affected
countries of the region.
Dengue in other regions
As described above, dengue is now endemic in all WHO regions except the WHO European
Region. Data available for the European region (http://data.euro.who.int/ cisid/) indicate that
most cases in the region have been reported by European Union member states, either as
incidents in overseas territories or importations from endemic countries. [See also a report
from the European Centre for Disease Prevention and Control]. However, in the past, dengue
has been endemic in some Balkan and Mediterranean countries of the region, and imported
cases in the presence of known mosquito vectors (e.g. Aedes albopictus) cannot exclude
future disease spread. Globally, reporting on dengue cases shows cyclical variation with high
epidemic years and non-epidemic years. Dengue often presents in the form of large
outbreaks. There is, however, also a seasonality of dengue, with outbreaks occurring in
different periods of the year. This seasonality is determined by peak transmission of the
disease, influenced by characteristics of the host, the vector and the agent.

Dengue case classification
Dengue has a wide spectrum of clinical presentations, often with unpredictable clinical
evolution and outcome. While most patients recover following a self-limiting non-severe
clinical course, a small proportion progress to severe disease, mostly characterized by plasma
leakage with or without haemorrhage. Intravenous rehydration is the therapy of choice; this
intervention can reduce the case fatality rate to less than 1% of severe cases. The group
progressing from non-severe to severe disease is difficult to define, but this is an important
concern since appropriate treatment may prevent these patients from developing more severe
clinical conditions. Triage, appropriate treatment, and the decision as to where this treatment
should be given (in a health care facility or at home) are influenced by the case classification
for dengue. This is even more the case during the frequent dengue outbreaks worldwide,
where health services need to be adapted to cope with the sudden surge in demand. Changes
in the epidemiology of dengue, as described in the previous sections, lead to problems with
the use of the existing WHO classification. Symptomatic dengue virus infections were
grouped into three categories: undifferentiated fever, dengue fever (DF) and dengue
haemorrhagic fever (DHF). DHF was further classified into four severity grades, with grades
III and IV being defined as dengue shock syndrome (DSS). There have been many reports of
difficulties in the use of this classification, which were summarized in a systematic literature
review. Difficulties in applying the criteria for DHF in the clinical situation, together with the
increase in clinically Chapter 1: Epidemiology, burden of disease and transmission
11CHAPTER 1 severe dengue cases which did not fulfi l the strict criteria of DHF, led to the
request for the classifi cation to be reconsidered. Currently the classifi cation into
DF/DHF/DSS continues to be widely used. A WHO/TDR-supported prospective clinical
multicentre study across dengue-endemic regions was set up to collect evidence about criteria
for classifying dengue into levels of severity. The study fi ndings confi rmed that, by using a
set of clinical and/or laboratory parameters, one sees a clear-cut difference between patients
with severe dengue and those with non-severe dengue. However, for practical reasons it was
desirable to split the large group of patients with non-severe dengue into two subgroups --
patients with warning signs and those without them. Criteria for diagnosing dengue (with or
without warning signs) and severe dengue are presented in Figure 1.4. It must be kept in mind
that even dengue patients without warning signs may develop severe dengue. Expert
consensus groups in Latin America (Havana, Cuba, 2007), South-East Asia (Kuala Lumpur,
Malaysia, 2007), and at WHO headquarters in Geneva, Switzerland in 2008 agreed that:
“dengue is one disease entity with different clinical presentations and often with

unpredictable clinical evolution and outcome”; the classifi cation into levels of severity has a
high potential for being of practical use in the clinicians’ decision as to where and how
intensively the patient should be observed and treated (i.e. triage, which is particularly useful
in outbreaks), in more consistent reporting in the national and international surveillance
system, and as an end-point measure in dengue vaccine and drug trials.
1.1.2 Dengue viruses
Dengue is caused by 40- to 50-mm single-stranded RNA viruses belonging to the Flavivirus
group. They are spherical and have a lipid envelope derived from host cell membranes. Four
species, known as serotypes, have been described,: DEN-1, DEN-2, DEN-3, and DEN-4. The
viral genome encodes three structural proteins (capsid, C, membrane protein, M, and
envelope glycoprotein, E) and seven non-structural proteins (NS1, NS2a, NS2b, NS3, NS4a,
NS4b, and NS5). The main biological properties of the viruses are located in the E protein.
Of the nonstructural proteins, some are involved in viral replication.3 Infection with one
dengue virus serotype results in specific immunity to that serotype only; theoretically,
individuals can be infected with all four serotypes. DEN-2 was the predominant serotype in
the 1980s and in the early 1990s, but in recent years, DEN-3 has been more predominant.
1.1.3 Transmission
Dengue is transmitted by the bite of an infected Aedes mosquito. The female Aedes mosquito
gets infected with the dengue virus after sucking blood from an infected person during acute
febrile illness (viremic phase). After an extrinsic incubation period of 8-10 days, the infected
mosquito transmits infection by biting and injecting infected salivary fluid into the wound of
another person. An infected female mosquito is capable of vertical transmission of the dengue
virus to its next generation, which is important for virus maintenance, but not for the
epidemiology of the disease. Vertical transmission from mother to child has been reported.
Aedes aegypti is the most important epidemic vector. A. albopictus and A. polynesiensis may
act as vectors in some geographic locations. Aedes aegypti is seen in abundance in at-risk
areas. It is found between latitudes 30º north and 20º south and at over 2,200 meters above
the sea level. Transmission occurs in geographically diverse areas, including subtropical and
tropical cities at various altitudes. The Aedes mosquito rests indoors, mainly in living rooms
and bedrooms, and in small collections of water, such as flowerpots or coconut shells.5,6

This maximizes man-vector contact and minimizes contact with insecticides sprayed
outdoors, hence hindering the control of this vector.7 Eggs can survive for long periods.
Improper disposal of garbage or inadequate wastewater drainage may be responsible for high
mosquito densities in endemic areas. Significant increases in the mosquito larval populations
are seen during the rainy season. This may be a reason why the epidemics of dengue tend to
coincide with the rainy season.5
1.1.4 Pathogenesis
After the bite of an infected mosquito, the average incubation period lasts 4 to 7 days (range
of 3-14 days), during which the patient may or may not experience symptoms, depending on
the virus strain, age, immune status, and other factors. This is followed by viremia, which is
associated with sudden onset of fever and constitutional symptoms lasting for 5-6 days (range
of 2 to 12 days). The dengue virus replicates within cells of the mononuclear phagocyte
lineage (macrophages, monocytes, and B cells). Additionally, infection of mast cells,
dendritic cells, and endothelial cells is known to occur.8 The virus may infect peripheral
blood leukocytes, liver, spleen, lymph node, bone marrow, thymus, heart, kidney, stomach,
lung, and possibly the brain, suggesting blood-brain barrier disruption.9 Dengue and dengue
hemorrhagic fever – Singhi S et al. Jornal de Pediatria - Vol. 83, No.2(Suppl), 2007 S23
Following the febrile (viremic) phase, the patient may either recover or progress to the
leakage phase, leading to DHF and/or dengue shock syndrome. Peak plasma viremia and
circulating levels of the dengue virus nonstructural protein NS1 correlate with the severity of
dengue infections.10 The increased number of infected cells results in increased production
of cytokines, including TNF-α and IFN-α, and other chemical mediators. TNF-α and IFN-α
also lead to activation of other dendritic cells, virally infected or non-infected.11,12 The
release of various cytokines and mediators is responsible for increased vascular permeability,
abnormal leakage of plasma, hypovolemia, shock, and hemostatic abnormalities. In addition,
there is evidence to show that endothelial cells also undergo apoptosis, which causes
disruption of the endothelial cell barrier, leading to the generalized vascular leak
syndrome.13 More severe infection occurs when a person is infected for a second time with a
different serotype in 2-4% of individuals. How a second dengue infection causes a severe
disease and why only some patients get severe disease remains unclear. It is suggested that
residual antibodies produced during the first infection are unable to neutralize a second
infection with another serotype, and the second infection, under the influence of enhancing
antibodies, results in severe infection and disease. This phenomenon is referred to as

antibody-dependent enhancement. The pre-existing nonneutralizing antibodies generated
from previous primary infection cross-react with viral serotypes involved in secondary
infections and bind to the virions, but do not neutralize them. Such antibody-coated virions
are taken up more rapidly than uncoated virus particles by tissues, dendritic cells, monocytes
and macrophages. This leads to a higher viral load and enhanced antigen presentation by the
infected dendritic cells to the T cells, resulting in extensive T-cell activation and proliferation
of memory T-cells. This extensive T-cell activation supposedly causes the T-cells to become
“stunned”, whereby their IFN-γ expression remains low.14 Common gross pathologic
findings in dengue infection include petechial hemorrhages and ecchymoses, serous pleural
and peritoneal effusions, and pulmonary edema. Vasculitis of small vessels in visceral and
soft tissues is found on microscopy, and so are focal midzonal hepatic necrosis,
subendocardial left ventricle hemorrhage, and gastric mucosal hemorrhage.
1.2 History
The first record of a case of probable dengue fever is in a Chinese medical encyclopedia from
the Jin Dynasty (265–420 AD) which referred to a "water poison" associated with flying
insects. The primary vector, A. aegypti, spread out of Africa in the 15th to 19th centuries due
in part to increased globalization secondary to the slave trade.There have been descriptions of
epidemics in the 17th century, but the most plausible early reports of dengue epidemics are
from 1779 and 1780, when an epidemic swept across Southeast Asia, Africa and North
America. From that time until 1940, epidemics were infrequent.
In 1906, transmission by the Aedes mosquitos was confirmed, and in 1907 dengue was the
second disease (after yellow fever) that was shown to be caused by a virus. Further
investigations by John Burton Cleland and Joseph Franklin Siler completed the basic
understanding of dengue transmission.
The marked spread of dengue during and after the Second World War has been attributed to
ecologic disruption. The same trends also led to the spread of different serotypes of the
disease to new areas and the emergence of dengue hemorrhagic fever. This severe form of the
disease was first reported in the Philippines in 1953; by the 1970s, it had become a major
cause of child mortality and had emerged in the Pacific and the Americas. Dengue
hemorrhagic fever and dengue shock syndrome were first noted in Central and South
America in 1981, as DENV-2 was contracted by people who had previously been infected
with DENV-1 several years earlier.

1.3 Prognosis
Most people with dengue recover without any ongoing problems.The risk of death among
those with severe dengue is 0.8% to 2.5%, and with adequate treatment this is less than
1%. However, those who develop significantly low blood pressure may have a fatality rate of
up to 26%.The risk of death among children less than five years old is four times greater than
among those over the age of 10. Elderly people are also at higher risk of a poor outcome.
Dengue is common in more than 120 countries. In 2013 it caused about 60 million
symptomatic infections worldwide, with 18% admitted to hospital and about 13,600
deaths. The worldwide cost of dengue case is estimated US$9 billion. For the decade of the
2000s, 12 countries in Southeast Asia were estimated to have about 3 million infections and
6,000 deaths annually. In 2019 the Philippines declared a national dengue epidemic due to the
deaths reaching 622 people that year. It is reported in at least 22 countries in Africa; but is
likely present in all of them with 20% of the population at risk. This makes it one of the most
common vector-borne diseases worldwide.
Infections are most commonly acquired in the urban environment. In recent decades, the
expansion of villages, towns and cities in the areas in which it is common, and the increased
mobility of people has increased the number of epidemics and circulating viruses. Dengue
fever, which was once confined to Southeast Asia, has now spread to southern China in East
Asia, countries in the Pacific Ocean and the Americas, and might pose a threat to Europe.
Rates of dengue increased 30 fold between 1960 and 2010. This increase is believed to be
due to a combination of urbanization, population growth, increased international travel,
and global warming. The geographical distribution is around the equator. Of the 2.5 billion
people living in areas where it is common 70% are from the WHO Southeast Asia Region
and Western Pacific Region. An infection with dengue is second only to malaria as a
diagnosed cause of fever among travelers returning from the developing world. It is the most
common viral disease transmitted by arthropods,and has a disease burden estimated at
1,600 disability-adjusted life years per million population. The World Health Organization
counts dengue as one of seventeen neglected tropical diseases.
Like most arboviruses, dengue virus is maintained in nature in cycles that involve preferred
blood-sucking vectors and vertebrate hosts.[ The viruses are maintained in the forests of
Southeast Asia and Africa by transmission from female Aedes mosquitos—of species other

than A. aegypti—to their offspring and to lower primates. In towns and cities, the virus is
primarily transmitted by the highly domesticated A. aegypti. In rural settings the virus is
transmitted to humans by A. aegypti and other species of Aedes such as A. albopictus. Both
these species had expanding ranges in the second half of the 20th century. In all settings the
infected lower primates or humans greatly increase the number of circulating dengue viruses,
in a process called amplification. One projection estimates that climate change, urbanization,
and other factors could result in more than 6 billion people at risk of dengue infection by
2080.
1.4 Etymology
The origins of the Spanish word dengue are not certain, but it is possibly derived
from dinga in the Swahili phrase Ka-dinga pepo, which describes the disease as being caused
by an evil spirit. Slaves in the West Indies having contracted dengue were said to have the
posture and gait of a dandy, and the disease was known as "dandy fever".
The term break-bone fever was applied by physician and United States Founding
Father Benjamin Rush, in a 1789 report of the 1780 epidemic in Philadelphia. In the report
title he uses the more formal term "bilious remitting fever". The term dengue fever came into
general use only after 1828. Other historical terms include "breakheart fever" and "la
dengue". Terms for severe disease include "infectious thrombocytopenic purpura" and
"Philippine", "Thai", or "Singapore hemorrhagic fever".

Chapter-02: Signs and symptom
2.1 Signs and symptom

Figure2.1: Schematicdepictionofthe symptomsofdenguefever

2.2 Clinical course of dengue fever
Typically, people infected with dengue virus are asymptomatic (80%) or have only mild
symptoms such as an uncomplicated fever. Others have more severe illness (5%), and in a small
proportion it is life-threatening. The incubation period (time between exposure and onset of

symptoms) ranges from 3 to 14 days, but most often it is 4 to 7 days. Therefore, travelers
returning from endemic areas are unlikely to have dengue fever if symptoms start more than
14 days after arriving home. Children often experience symptoms similar to those of
the common cold and gastroenteritis (vomiting and diarrhea) and have a greater risk of severe
complications, though initial symptoms are generally mild but include high fever.
2.3 Clinical course
The characteristic symptoms of dengue are sudden-onset fever, headache (typically located
behind the eyes), muscle and joint pains, and a rash. An alternative name for dengue, "breakbone
fever", comes from the associated muscle and joint pains. The course of infection is divided into
three phases: febrile, critical, and recover.
The febrile phase involves high fever, potentially over 40 °C (104 °F), and is associated with
generalized pain and a headache; this usually lasts two to seven days. Nausea and vomiting may
also occur. A rash occurs in 50–80% of those with symptom in the first or second day of
symptoms as flushed skin, or later in the course of illness (days 4–7), as a measles-like rash. A
rash described as "islands of white in a sea of red" has also been observed.Some petechiae (small
red spots that do not disappear when the skin is pressed, which are caused by broken capillaries)
can appear at this point, as may some mild bleeding from the mucous membranes of the mouth
and nose.The fever itself is classically biphasic or saddleback in nature, breaking and then
returning for one or two days.
In some people, the disease proceeds to a critical phase as fever resolves.During this period,
there is leakage of plasma from the blood vessels, typically lasting one to two days.This may
result in fluid accumulation in the chest and abdominal cavity as well as depletion of fluid from
the circulation and decreased blood supply to vital organs. There may also be organ dysfunction
and severe bleeding, typically from the gastrointestinal tract. Shock (dengue shock syndrome)
and hemorrhage (dengue hemorrhagic fever) occur in less than 5% of all cases of
dengue;however, those who have previously been infected with other serotypes of dengue virus
("secondary infection") are at an increased risk. This critical phase, while rare, occurs relatively
more commonly in children and young adults.
The recovery phase occurs next, with resorption of the leaked fluid into the bloodstream. This
usually lasts two to three days. The improvement is often striking, and can be accompanied with

severe itching and a slow heart rate. Another rash may occur with either a maculopapular or
a vasculitic appearance, which is followed by peeling of the skin. During this stage, a fluid
overload state may occur; if it affects the brain, it may cause a reduced level of
consciousness or seizures. A feeling of fatigue may last for weeks in adults.
Figure2.2: Therash ofdenguefeverin the acute stageof the infection blancheswhen
pressed

Figure2.3 Therashthat commonlyformsduringthe recoveryfromdenguefeverwithits
classicislandsofwhiteina sea ofred.
2.4 Associatedproblems
Dengue can occasionally affect several other body systems,either in isolation or along with the
classic dengue symptoms. A decreased level of consciousness occurs in 0.5–6% of severe cases,
which is attributable either to inflammation of the brain by the virus or indirectly as a result of
impairment of vital organs, for example, the liver.
Other neurological disorders have been reported in the context of dengue, such as transverse
myelitis and Guillain–Barré syndrome. Infection of the heart and acute liver failure are among
the rarer complications.
A pregnant woman who develops dengue is at higher risk of miscarriage, low birth weight birth,
and premature birth.

2.5 Cause
2.5.1 Virology
Figure2.4 showingdenguevirus e(4theclusterofdarkdotsnear the center)
Dengue fever virus (DENV) is an RNA virus of the family Flaviviridae; genus Flavivirus. Other
members of the same genus include yellow fever virus, West Nile virus, Zika virus, St. Louis
encephalitis virus, Japanese encephalitis virus, tick-borne encephalitis virus, Kyasanur forest
disease virus, and Omsk hemorrhagic fever virus. Most are transmitted by arthropods(mosquitos
or ticks), and are therefore also referred to as arboviruses (arthropod-borne viruses).
The dengue virus genome (genetic material) contains about 11,000 nucleotide bases,
which code for the three different types of protein molecules (C, prM and E) that form the virus
particle and seven other non-structural protein molecules (NS1, NS2a, NS2b, NS3, NS4a, NS4b,
NS5) that are found in infected host cells only and are required for replication of the virus. There
are five strains of the virus, called serotypes, of which the first four are referred to as DENV-1,
DENV-2, DENV-3 and DENV-4.The fifth type was announced in 2013. The distinctions
between the serotypes are based on their antigenicity.

2.5.2 Transmission
Figure2.5 Themosquito Aedesaegypti feedingonahuman host
Dengue virus is primarily transmitted by Aedes mosquitos, particularly A. aegypti. These
mosquitos usually live between the latitudes of 35° North and 35° South below an elevation of
1,000 metres (3,300 ft). They typically bite during the early morning and in the evening, but they
may bite and thus spread infection at any time of day. Other Aedes species that transmit the
disease include A. albopictus, A. polynesiensis and A. scutellaris. Humans are the primary host of
the virus,but it also circulates in nonhuman primates. An infection can be acquired via a single
bite. A female mosquito that takes a blood meal from a person infected with dengue fever, during
the initial 2- to 10-day febrile period, becomes itself infected with the virus in the cells lining its
gut. About 8–10 days later, the virus spreads to other tissues including the mosquito's salivary
glands and is subsequently released into its saliva. The virus seems to have no detrimental effect
on the mosquito, which remains infected for life.Aedes aegypti is particularly involved, as it
prefers to lay its eggs in artificial water containers, to live in close proximity to humans, and to
feed on people rather than other vertebrates.
Dengue can also be transmitted via infected blood products and through organ donation. In
countries such as Singapore, where dengue is endemic, the risk is estimated to be between 1.6
and 6 per 10,000 transfusions. Vertical transmission (from mother to child) during pregnancy or

at birth has been reported.Other person-to-person modes of transmission, including sexual
transmission, have also been reported, but are very unusual. The genetic variation in dengue
viruses is region specific, suggestive that establishment into new territories is relatively
infrequent, despite dengue emerging in new regions in recent decades.
2.5.3 Predisposition
Severe disease is more common in babies and young children, and in contrast to many other
infections, it is more common in children who are relatively well nourished. Other risk
factors for severe disease include female sex, high body mass index,[
and viral load.While each
serotype can cause the full spectrum of disease, virus strain is a risk factor. Infection with one
serotype is thought to produce lifelong immunity to that type, but only short-term protection
against the other three. The risk of severe disease from secondary infection increases if someone
previously exposed to serotype DENV-1 contracts serotype DENV-2 or DENV-3, or if someone
previously exposed to DENV-3 acquires DENV-2.Dengue can be life-threatening in people
with chronic diseasessuch as diabetes and asthma.
Polymorphisms (normal variations) in particular genes have been linked with an increased risk of
severe dengue complications. Examples include the genes coding for the
proteins TNFα, mannan-binding lectin, CTLA4, TGFβ, DC-SIGN, PLCE1, and
particular forms of human leukocyte antigen from gene variations of HLA-B. A common genetic
abnormality, especially in Africans, known as glucose-6-phosphate dehydrogenase deficiency,
appears to increase the risk. Polymorphisms in the genes for the vitamin D
receptorand FcγR seem to offer protection against severe disease in secondary dengue infection.
2.6 Mechanism
When a mosquito carrying dengue virus bites a person, the virus enters the skin together with the
mosquito's saliva. It binds to and enters white blood cells, and reproduces inside the cells while
they move throughout the body. The white blood cells respond by producing several signaling
proteins, such as cytokines and interferons, which are responsible for many of the symptoms,
such as the fever, the flu-like symptoms, and the severe pains. In severe infection, the virus
production inside the body is greatly increased, and many more organs (such as the liver and
the bone marrow) can be affected. Fluid from the bloodstream leaks through the wall of small
blood vessels into body cavities due to capillary permeability. As a result, less blood circulates in

the blood vessels, and the blood pressure becomes so low that it cannot supply sufficient blood to
vital organs. Furthermore, dysfunction of the bone marrow due to infection of the stromal
cells leads to reduced numbers of platelets, which are necessary for effective blood clotting; this
increases the risk of bleeding, the other major complication of dengue fever.
2.6.1 Viral replication
Once inside the skin, dengue virus binds to Langerhans cells (a population of dendritic cells in
the skin that identifies pathogens). The virus enters the cells through binding between viral
proteins and membrane proteins on the Langerhans cell, specifically, the C-type lectins called
DC-SIGN, mannose receptor and CLEC5A.[30]
DC-SIGN, a non-specific receptor for foreign
material on dendritic cells, seems to be the main point of entry. The dendritic cell moves to the
nearest lymph node. Meanwhile, the virus genome is translated in membrane-bound vesicles on
the cell's endoplasmic reticulum, where the cell's protein synthesis apparatus produces new viral
proteins that replicate the viral RNA and begin to form viral particles. Immature virus particles
are transported to the Golgi apparatus, the part of the cell where some of the proteins receive
necessary sugar chains (glycoproteins). The now mature new viruses are released by exocytosis.
They are then able to enter other white blood cells, such as monocytes and macrophages.
The initial reaction of infected cells is to produce interferon, a cytokine that raises many defenses
against viral infection through the innate immune system by augmenting the production of a
large group of proteins mediated by the JAK-STAT pathway. Some serotypes of the dengue
virus appear to have mechanisms to slow down this process. Interferon also activates
the adaptive immune system, which leads to the generation of antibodies against the virus as well
as T cells that directly attack any cell infected with the virus.Various antibodies are generated;
some bind closely to the viral proteins and target them for phagocytosis (ingestion by specialized
cells and destruction), but some bind the virus less well and appear instead to deliver the virus
into a part of the phagocytes where it is not destroyed but can replicate further.

2.6.2 Severe disease
Figure2.6: In antibody-dependentenhancement(ADE),antibodiesbindto bothviral
particlesandFc gamma receptorsexpressedonimmunecells,increasingthelikelihoodthat
the viruseswill infectthosecells.
It is not entirely clear why secondary infection with a different strain of dengue virus places
people at risk of dengue hemorrhagic fever and dengue shock syndrome. The most widely
accepted hypothesis is that of antibody-dependent enhancement (ADE). The exact mechanism
behind ADE is unclear. It may be caused by poor binding of non-neutralizing antibodies and
delivery into the wrong compartment of white blood cells that have ingested the virus for
destruction. There is a suspicion that ADE is not the only mechanism underlying severe dengue-
related complications, and various lines of research have implied a role for T cells and soluble
factors such as cytokines and the complement system.
Severe disease is marked by the problems of capillary permeability (an allowance of fluid and
protein normally contained within the blood to pass) and disordered blood clotting. These
changes appear associated with a disordered state of the endothelial glycocalyx, which acts as
a molecular filter of blood components.Leaky capillaries (and the critical phase) are thought to
be caused by an immune system response. Other processes of interest include infected cells that
become necrotic—which affect both coagulation and fibrinolysis (the opposing systems of blood
clotting and clot degradation)—and low platelets in the blood, also a factor in normal clotting.

Chapter-03: Diagnosis and Prevention
3.1 Diagnosis
The diagnosis of dengue is typically made clinically, on the basis of reported symptoms
and physical examination; this applies especially in endemic areas. However, early disease
can be difficult to differentiate from other viral infections. A probable diagnosis is based on
the findings of fever plus two of the following: nausea and vomiting, rash, generalized
pains, low white blood cell count, positive tourniquet test, or any warning sign (see table) in
someone who lives in an endemic area. Warning signs typically occur before the onset of
severe dengue. The tourniquet test, which is particularly useful in settings where no
laboratory investigations are readily available, involves the application of a blood pressure
cuff at between the diastolic and systolic pressure for five minutes, followed by the counting
of any petechialhemorrhages; a higher number makes a diagnosis of dengue more likely with
the cut off being more than 10 to 20 per 1 inch2 (6.25 cm2).
The diagnosis should be considered in anyone who develops a fever within two weeks of
being in the tropics or subtropics. It can be difficult to distinguish dengue fever
and chikungunya, a similar viral infection that shares many symptoms and occurs in similar
parts of the world to dengue. Often, investigations are performed to exclude other conditions
that cause similar symptoms, such as malaria, leptospirosis, viral hemorrhagic fever, typhoid
fever, meningococcal disease, measles, and influenza. Zika fever also has similar symptoms
as dengue.
The earliest change detectable on laboratory investigations is a low white blood cell count,
which may then be followed by low platelets and metabolic acidosis. A moderately elevated
level of aminotransferase (AST and ALT) from the liver is commonly associated with low
platelets and white blood cells. In severe disease, plasma leakage results
in hemoconcentration (as indicated by a rising hematocrit) and hypoalbuminemia. Pleural
effusions or ascitescan be detected by physical examination when large, but the
demonstration of fluid on ultrasound may assist in the early identification of dengue shock
syndrome. The use of ultrasound is limited by lack of availability in many settings. Dengue
shock syndrome is present if pulse pressure drops to ≤ 20 mm Hg along with peripheral
vascular collapse. Peripheral vascular collapse is determined in children via delayed capillary
refill, rapid heart rate, or cold extremities. While warning signs are an important aspect for
early detection of potential serious disease, the evidence for any specific clinical or laboratory
marker is weak.

3.2 Classification
The World Health Organization's 2009 classification divides dengue fever into two groups:
uncomplicated and severe. This replaces the 1997 WHO classification, which needed to be
simplified as it had been found to be too restrictive, though the older classification is still
widely used including by the World Health Organization's Regional Office for Southeast
Asia as of 2011.Severe dengue is defined as that associated with severe bleeding, severe
organ dysfunction, or severe plasma leakage while all other cases are uncomplicated. The
1997 classification divided dengue into an undifferentiated fever, dengue fever, and dengue
hemorrhagic fever.Dengue hemorrhagic fever was subdivided further into grades I–IV. Grade
I is the presence only of easy bruising or a positive tourniquet test in someone with fever,
grade II is the presence of spontaneous bleeding into the skin and elsewhere, grade III is the
clinical evidence of shock, and grade IV is shock so severe that blood pressure
and pulse cannot be detected. Grades III and IV are referred to as "dengue shock syndrome".
3.3 Laboratory tests
Figure3.1 Graphofwhenlaboratorytestsfordenguefeverbecomepositive.Dayzero
refersto the start of symptoms,1st refersto in thosewith a primaryinfection,and2nd
refersto in thosewitha secondaryinfection.[25]
The diagnosis of dengue fever may be confirmed by microbiological laboratory testing. This
can be done by virus isolation in cell cultures, nucleic acid detection by PCR,

viral antigen detection (such as for NS1) or specific antibodies(serology). Virus isolation and
nucleic acid detection are more accurate than antigen detection, but these tests are not widely
available due to their greater cost. Detection of NS1 during the febrile phase of a primary
infection may be greater than 90% sensitive however is only 60–80% in subsequent
infections. All tests may be negative in the early stages of the disease. PCR and viral antigen
detection are more accurate in the first seven days. In 2012 a PCR test was introduced that
can run on equipment used to diagnose influenza; this is likely to improve access to PCR-
based diagnosis.
These laboratory tests are only of diagnostic value during the acute phase of the illness with
the exception of serology. Tests for dengue virus-specific antibodies, types IgG and IgM, can
be useful in confirming a diagnosis in the later stages of the infection. Both IgG and IgM are
produced after 5–7 days. The highest levels (titres) of IgM are detected following a primary
infection, but IgM is also produced in reinfection. IgM becomes undetectable 30–90 days
after a primary infection, but earlier following re-infections. IgG, by contrast, remains
detectable for over 60 years and, in the absence of symptoms, is a useful indicator of past
infection. After a primary infection, IgG reaches peak levels in the blood after 14–21 days. In
subsequent re-infections, levels peak earlier and the titres are usually higher. Both IgG and
IgM provide protective immunity to the infecting serotype of the virus. In testing for IgG and
IgM antibodies there may be cross-reactivity with other flaviviruses which may result in a
false positive after recent infections or vaccinations with yellow fever virus or Japanese
encephalitis. The detection of IgG alone is not considered diagnostic unless blood samples
are collected 14 days apart and a greater than fourfold increase in levels of specific IgG is
detected. In a person with symptoms, the detection of IgM is considered diagnostic.
3.4 Prevention
Prevention of Dengue Fever is easy, cheap and better. What is required are some simple
measures for – • Preventing breeding of Aedes mosquitoes • Protection from Aedes
mosquitoes’ bites. For protection against mosquitoes – 1. Mosquitoes breed only in water
sources such as stagnant water in drains and ditches, room air coolers, broken bottles, old
discarded tyres, containers and similar sources. • Don’t allow water to remain stagnant in and
around your house. Fill the ditches. Clean the blocked drains. Empty the room air coolers and
flower vases completely atleast once in seven days and let them dry. Dispose off old
containers, tins and tyres etc. properly. • Keep the water tanks and water containers tightly
covered so that the mosquitoes can not enter them and start breeding. • Wherever it is not

possible to completely drain the water off from room cooler, water tanks etc., it is advised to
put about two tablespoons (30 ml.) of petrol or kerosene oil into them for each 100 litres of
water. This will prevent mosquito breeding. Repeat it every week. • You can also put some
types of small fish (Gambusia, Lebister) which eat mosquito larvae into these water
collections. These fish can be obtained from the local administrative bodies (e.g., Malaria
Officer’s office in the area). 6 • Wherever possible, practicable and affordable, prevent entry
of mosquitoes into the house by keeping wire mesh on windows and doors. • Use mosquito
repellent sprays, creams, coils, mats or liquids to drive away/ kill the mosquitoes. Use of
googal smoke is a good indigenous method for getting rid of mosquitoes. • Wear clothes
which cover the body as much as possible. This is more relevant in case of children. Nickers
and T-shirts are better avoided during the season of Malaria and Dengue fever, i.e., from July
to October. • Don’t turn away spray workers whenever they come to spray your house. It is in
your own interest to get the house sprayed. • Use insecticidal sprays in all areas within the
house atleast once a week. Don’t forget to spray behind the photo-frames, curtains, calendars;
corners of house, stores. • Keep the surroundings of your house clean. Don’t litter garbage.
Don’t allow wild herbs etc. to grow around your house (atleast in a radius of about 100
metres around your house). They act as hiding and resting places for mosquitoes. • Do inform
and take help from your local health centre, panchayat or municipality in case you notice
abnormal density of mosquitoes or too many cases of fever are occurring in your area. 7 It is
good to remember that Aedes mosquitoes bite even during daytime and hence you should
take precautions against their bite during day time also. • If fencing of the doors and windows
is not possible due to any reason, spray the entire house daily with pyrethrum solution. •
Dengue fever occurs most frequently in India in the months of July to October because this
season provides very suitable conditions for breeding of mosquitoes. Hence all these
preventive steps must be taken during the season. • Lastly, it is advisable to always keep the
patient of Dengue fever under a mosquito net in the first 5-6 days of the illness so that
mosquitoes don’t have an access to him/her. This will help in reduction in spread of Dengue
fever to other persons in the Community. Source : "Diseases and Conditions with Epidemic
Potential" by Dr. Bir Singh Published by : VHAI, 2000 If you ever notice that many persons
have suffered from an illness which may appear to be Dengue Fever, please inform this to the
local health authorities at the earliest. This will help in preventing the disease acquiring
epidemic proportions.

Figure3.2 A 1920sphotographofeffortsto dispersestandingwaterandthus decrease
mosquito populations
Prevention depends on control of and protection from the bites of the mosquito that transmits
it. The World Health Organization recommends an Integrated Vector Control program
consisting of five elements:
1. Advocacy, social mobilization and legislation to ensure that public health bodies and
communities are strengthened;
2. Collaboration between the health and other sectors (public and private);
3. An integrated approach to disease control to maximize the use of resources;
4. Evidence-based decision making to ensure any interventions are targeted
appropriately; and
5. Capacity-building to ensure an adequate response to the local situation.
The primary method of controlling A. aegypti is by eliminating its habitats. This is done by
getting rid of open sources of water, or if this is not possible, by
adding insecticides or biological control agents to these areas. Generalized spraying
with organophosphate or pyrethroid insecticides, while sometimes done, is not thought to be
effective. Reducing open collections of water through environmental modification is the
preferred method of control, given the concerns of negative health effects from insecticides
and greater logistical difficulties with control agents. People can prevent mosquito bites by

wearing clothing that fully covers the skin, using mosquito netting while resting, and/or the
application of insect repellent (DEET being the most effective). While these measures can be
an effective means of reducing an individual's risk of exposure, they do little in terms of
mitigating the frequency of outbreaks, which appear to be on the rise in some areas, probably
due to urbanization increasing the habitat of A. aegypti. The range of the disease also appears
to be expanding possibly due to climate change.
3.5 Vaccine
In 2016 a partially effective vaccine for dengue fever became commercially available in the
Philippines and Indonesia. It has been approved for use by Mexico, Brazil, El Salvador, Costa
Rica, Singapore, Paraguay, much of Europe, and the United States. The vaccine is only
recommended in individuals who have had a prior dengue infection or in populations where
most (>80%) of people have been infected by age 9. In those who have not had a prior
infection there is evidence it may worsen subsequent infections. For this
reason Prescrire does not see it as suitable for wide scale immunization, even in areas were
the disease is common.
The vaccine is produced by Sanofi and goes by the brand name Dengvaxia. It is based on a
weakened combination of the yellow fever virus and each of the four dengue
serotypes. Studies of the vaccine found it was 66% effective and prevented more than 80 to
90% of severe cases.This is less than wished for by some.In Indonesia it costs about US$207
for the recommended three doses.
Given the limitations of the current vaccine, research on vaccines continues, and the fifth
serotype may be factored in. One of the concerns is that a vaccine could increase the risk of
severe disease through antibody-dependent enhancement (ADE). The ideal vaccine is safe,
effective after one or two injections, covers all serotypes, does not contribute to ADE, is
easily transported and stored, and is both affordable and cost-effective.

3.6 Anti-dengue day
Figure3.3 A posterin Tampines,Singapore,notifyingpeoplethatthereare ten or more
casesof dengueinthe neighbourhood(November2015).
International Anti-Dengue Day is observed every year on 15 June.The idea was first agreed
upon in 2010 with the first event held in Jakarta, Indonesia in 2011. Further events were held
in 2012 in Yangon, Myanmar and in 2013 in Vietnam. Goals are to increase public awareness
about dengue, mobilize resources for its prevention and control and, to demonstrate the
Southeast Asian region's commitment in tackling the disease.

4.1 Management
There are no specific antiviral drugs for dengue; however, maintaining proper fluid balance is
important. Treatment depends on the symptoms. Those who can drink, are passing urine, have no
"warning signs" and are otherwise healthy can be managed at home with daily follow-up and oral
rehydration therapy. Those who have other health problems, have "warning signs", or cannot
manage regular follow-up should be cared for in hospital. In those with severe dengue care
should be provided in an area where there is access to an intensive care unit.
Intravenous hydration, if required, is typically only needed for one or two days. In children
with shock due to dengue a rapid dose of 20 mL/kg is reasonable.The rate of fluid administration
is then titrated to a urinary output of 0.5–1 mL/kg/h, stable vital signs and normalization of
hematocrit. The smallest amount of fluid required to achieve this is recommended.
Invasive medical procedures such as nasogastric intubation, intramuscular injections and arterial
punctures are avoided, in view of the bleeding risk. Paracetamol(acetaminophen) is used for
fever and discomfort while NSAIDs such as ibuprofen and aspirin are avoided as they might
aggravate the risk of bleeding. Blood transfusion is initiated early in people presenting with
unstable vital signs in the face of a decreasing hematocrit, rather than waiting for the
hemoglobin concentration to decrease to some predetermined "transfusion trigger" level. Packed
red blood cells or whole blood are recommended, while platelets and fresh frozen plasma are
usually not. There is not enough evidence to determine if corticosteroids have a positive or
negative effect in dengue fever.
During the recovery phase intravenous fluids are discontinued to prevent a state of fluid
overload.If fluid overload occurs and vital signs are stable, stopping further fluid may be all that
is needed. If a person is outside of the critical phase, a loop diuretic such as furosemide may be
used to eliminate excess fluid from the circulation.
4.2 Treatment
If it is classical (simple) Dengue Fever, the patient can be managed at home. As it is a self-
limiting disease, the treatment is purely supportive 4 and symptomatic – e.g. – • Keep the fever
low by giving paracetamol tablet or syrup as per health worker’s advise. • Avoid giving Aspirin
or Dispirin tablets to the patient • If fever is more than 102°F, carry out hydrotherapy to bring
down the temperature. • Give plenty of fluids water, shikanji etc. to the patient. • Continue

normal feeding. In fever, the body, infact, requires more food. • Allow the patient to rest. If any
of the symptoms indicative of DHF or DSS develop, rush the patient to the nearest hospital at the
earliest where appropriate investigations will be carried out and necessary treatment instituted,
e.g., transfusion of fluids or platelets (a kind of blood cells which become low in DHF and DSS).
Please remember that every patient does not require blood platelet transfusion. Please remember
: Even DHF and DSS can be managed successfully if a correct diagnosis is made and the
treatment is started early
4.2.1 Blooddonation
Outbreaks of dengue fever increase the need for blood products while decreasing the number of
potential blood donors due to potential infection with the virus. Someone who has a dengue
infection is typically not allowed to donate blood for at least the next six months.
4.2.2 Awareness efforts
A National Dengue Day is held in India on 16 May in an effort to raise awareness in affected
countries. Efforts are ongoing as of 2019 to make it a global event. The Philippines has an
awareness month in June since 1998.
4.3 Research
Research efforts to prevent and treat dengue include various means of vector control, vaccine
development, and antiviral drugs.

4.3.1 Vector
Figure4.1 Publichealthofficersreleasing P.reticulatafryinto an artificial lake inthe Lago
Nortedistrict of Brasília,Brazil,aspart ofa vectorcontrol effort
With regards to vector control, a number of novel methods have been used to reduce mosquito
numbers with some success including the placement of the guppy (Poecilia reticulata)
or copepods in standing water to eat the mosquito larvae.There are also trials with genetically
modified male A. aegypti that after release into the wild mate with females, and render their
offspring unable to fly.
4.3.2 Wolbachia
Attempts are ongoing to infect the mosquito population with bacteria of the genus Wolbachia,
which makes the mosquitos partially resistant to dengue virus. While artificially induced
infection with Wolbachia is effective, it is unclear if naturally acquired infections are
protective. Work is still ongoing as of 2015 to determine the best type of Wolbachia to use.
4.3.3 Treatment
Apart from attempts to control the spread of the Aedes mosquito there are ongoing efforts to
develop antiviral drugs that would be used to treat attacks of dengue fever and prevent severe
complications. Discovery of the structure of the viral proteins may aid the development of
effective drugs. There are several plausible targets. The first approach is inhibition of the

viral RNA-dependent RNA polymerase (coded by NS5), which copies the viral genetic material,
with nucleoside analogs. Secondly, it may be possible to develop specific inhibitors of the
viral protease (coded by NS3), which splices viral proteins. Finally, it may be possible to
develop entry inhibitors, which stop the virus entering cells, or inhibitors of the 5′
capping process, which is required for viral replication.
6.1 Overview Primary prevention of dengue is currently possible only with vector control and
personal protection from the bites of infected mosquitoes. However, the development of vaccines
and drugs has the potential to change this. This chapter describes the current development of
vaccines (section 6.2) and drugs (section 6.3). 6.2 Dengue vaccines 6.2.1 Overview Despite
formidable challenges to developing tetravalent dengue vaccines, significant progress has been
made in recent years and the pace towards clinical efficacy trials has accelerated substantially
(1,2,3,4). Box 6.1 summarizes the complexity of developing a dengue vaccine. Triggered by the
continued unchecked spread of dengue worldwide, there has been renewed interest in dengue by
researchers, funding agencies, policymakers and vaccine manufacturers alike. The creation of
public–private partnerships for product development has facilitated the process. Recent studies of
the burden of disease have quantified the cost of dengue both to the public sector and to
households and have demonstrated the potential cost-effectiveness of a dengue vaccine (5,6,7,8).
The vaccine pipeline is now sufficiently advanced for it to be possible to have a firstgeneration
dengue vaccine licensed within the next five to seven years (3). In addition, a number of diverse
candidates are at earlier stages of evaluation and could become second-generation vaccines. 6.2.2
Product development A primary immunological mechanism that confers protection from dengue
illness is virus neutralization through antibodies, and all current dengue vaccine candidates aim
to elicit high levels of neutralizing antibody. The increasing co-circulation of the four dengue
virus types means that a vaccine is needed that protects against all four of them; hence, the
vaccine needs to be tetravalent. Moreover, the induction of protective, neutralizing antibody
responses against all four serotypes of dengue virus simultaneously should avoid the theoretical
concern of vaccine-ind 138 Dengue: Guidelines for diagnosis, treatment, prevention and control
• The viruses should replicate well in cell culture and be sufficiently immunogenic to provide
long-lasting immunity in humans, so that low doses can be used. • A balanced immune response
to all four dengue viruses must be elicited. • The genetic basis for attenuation must be known and
must be stable (4). Several live attenuated vaccines are in advanced stages of development. One

is a chimeric tetravalent vaccine in which the structural genes (prM and E) of each of the four
dengue viruses were inserted individually to replace those of yellow fever virus in the backbone
of the yellow fever 17D vaccine. Thus, the nonstructural genes of yellow fever are provided to
allow replication of the chimeric virus, and attenuation is imparted by the yellow fever portion of
the chimera. Monovalent vaccines, as well as tetravalent mixtures of all four viruses, have been
given to human volunteers of varying ages in phase 1 and phase 2 trials in both non-endemic and
endemic regions. At least two doses were required to achieve high rates of tetravalent
neutralizing antibodies, and somewhat higher seroconversion rates were observed in subjects
with pre-existing immunity to yellow fever (2). Another comprises strains of the four serotypes
of the dengue virus, each attenuated by passage in primary dog kidney cells and initially
prepared as candidate vaccines in fetal rhesus monkey lung cells (FRhL). Each attenuated
dengue virus was rederived by transfecting cells with purified viral RNA. Original and rederived
attenuated viruses have been extensively tested both individually and in tetravalent formulation
in phase 1 and phase 2 trials in human volunteers of different ages. Tetravalent anti-DEN
neutralizing antibodies are raised to high rates following the administration of at least two doses
at an interval of six months, especially if volunteers have previously been exposed to
flaviviruses. Other vaccine candidates in phase 1 testing include live attenuated viruses. Here,
vaccine development is being approached in two ways: (i) via direct removal of 30 nucleotides in
the 3’ untranslated region of DEN-1 and DEN-4, and (ii) the construction of chimeric viruses
consisting of DEN-2 and DEN-3 structural genes in the non-structural backbone of the DEN-4
strain with 30 nucleotides deleted from the 3’ untranslated region. Satisfactory attenuation,
immunogenicity and protection have been obtained in rhesus monkeys for each of the four
dengue viruses in this way (4). Phase 1 testing has taken place with all four monovalent vaccines.
Dengue vaccines in advanced preclinical development include DEN-DEN chimeras. In this
vaccine, the prM and E protein genes of DEN-1, DEN-3 and DEN-4 were each inserted into the
infectious clone of PDK-passaged, attenuated DEN-2 (PDK53). The three attenuating mutations
are located outside the structural protein genes of PDK53 and appear to be quite stable. The
tetravalent vaccine produced by combining the four chimeric dengue viruses is protective when
administered to mice. Monkey challenge experiments have been conducted but preparations for
clinical trials are underway. Several DNA vaccines designed to deliver structural dengue viral
genes into cells have been generated, and a monovalent DEN-1 DNA vaccine is currently

undergoing phase 1 testing. In addition, candidate vaccines that have successfully protected
monkeys from viraemic challenge include recombinant 80% envelope protein from the four DEN
serotypes in conjunction with DEN-2 NS1 administered with several new-generation adjuvants.
There is also work in progress on subunit vaccines based on domain III 139 Chapter 6. New
avenues CHAPTER 6 of the E protein, which is considered to be the principal neutralizing
epitope region of the virus, employing different strategies to increase immunogenicity. A
tetravalent replication-defective-recombinant adenovirus (cAdVaX) has also been prepared, as
have formalin-inactivated vaccines of the four dengue viruses. Finally, prime-boost strategies
combining vaccines of distinct formulations are under investigation. 6.2.3 Challenges Since
dengue is caused by four serologically related viruses, the first major problem in developing a
dengue vaccine is to develop not just one immunogen but four immunogens that will induce a
protective immune response against all four viruses simultaneously. Therefore, the vaccine must
be tetravalent. Interference between the four vaccine viruses must be avoided or overcome, and
neutralizing titres to all four viruses need to be achieved regardless of the previous immune
status of the vaccinated individuals. Thus, the tetravalent formulations must balance viral
interference with longlasting immunogenicity and reactogenicity. The second issue is the lack of
a validated correlate of protection since the mechanism of protective immunity against DEN
infection is not fully understood. A wealth of data suggests that neutralizing antibodies are the
main effector of protection against DEN virus infection. However, neither the precise antibody
titres nor neutralizing epitopes nor the contributions of other immune mechanisms to protection
have been defined. Further studies are necessary to elucidate the mechanism of protective
immunity so that correlates of protection can be established to demonstrate that the candidate
vaccines induce a protective immune response (9). The dengue viruses are arboviruses whose
normal transmission cycle involves mosquitoes (most commonly Ae. aegypti and Ae. albopictus)
with humans as the vertebrate host, without relying on other animal reservoirs. Herein lies the
third problem. Two animal models (mice and non-human primates) are used to evaluate
candidate vaccines, but neither of these faithfully recapitulates both the disease outcome and the
immune response in humans. Mice are often used as a small animal model to evaluate initially
the ability of candidate vaccines to induce a protective immune response, and good progress has
been made recently in developing mouse models for DEN virus infection and disease. However,
the results are not always predictive of what will happen in higher animal species – i.e. a

candidate vaccine that protects mice may not be as effective in other animal models. The second
animal model is the non-human primate, and a variety of species have been used as models to
evaluate candidate dengue vaccines. Unfortunately, non-human primates do not present clinical
disease but do demonstrate viraemia (originally measured as infectivity, now normally measured
by real-time RT-PCR and immunological parameters as proxies). Clearly, the mouse and non-
human primate models must be used to evaluate candidate dengue vaccines before they are tested
in humans. However, unexpected discordance has occasionally been observed between
preclinical and clinical outcomes (10). The fourth challenge for the development of dengue
vaccines is the potential for immune enhancement, including antibody-dependent enhancement.
It is clear that an infection by one dengue virus leads to lifelong protective immunity against the
infecting virus, i.e. homotypic immunity. However, many studies have shown that some
secondary DEN infections (i.e. infection by one dengue virus followed by infection by a different
DEN serotype) can lead to severe disease (DHF/DSS) and that anti-DEN antibodies passively
140 Dengue: Guidelines for diagnosis, treatment, prevention and control transferred from
mothers to infants increase the risk of DHF/DSS in the infants for a certain period of time. Thus,
there is theoretically a danger that a dengue vaccine could potentially cause severe disease
(including DHF or DSS) in vaccine recipients if solid immunity was not established against all
four serotypes. It should be emphasized that, to date, there is no evidence that a vaccine recipient
who has received a candidate vaccine has subsequently succumbed to severe disease. Rather,
vaccine recipients have shown evidence of immunity for varying lengths of time. This may be
influenced by the candidate vaccine. Also vaccine recipients may have been exposed to less
symptomatic DEN infections than control groups, although this is based on small numbers thus
far (11). Nonetheless, the risk of immune enhancement by a candidate vaccine must be evaluated
through prolonged follow-up of vaccinated cohorts. Box 6.1 The complexity of developing a
dengue vaccine Development • Need for a tetravalent vaccine with not just one but four
immunogens that will give a balanced immune response whereby a protective long-lasting
immunity is induced against all four viruses simultaneously (balancing viral interference,
immunogenicity, and reactogenicity). • Lack of immune correlate of protection since the
mechanism of protective immunity against DEN infection is only partially understood. It is
assumed that neutralizing antibodies are the main effector of protection against DEN infection. •
Lack of a suitable animal model that recapitulates human disease and can be used to evaluate

candidate vaccines. • Potential immunopathogenesis, including antibody-dependent enhancement
Implementation • Need for long-term follow-up. • Need for testing in both Asia and the
Americas. • Ideally, can be tested against all four DEN serotypes. • The exact location, timing
and serotype/genotype composition of dengue epidemics varies from year to year and is
somewhat unpredictable. 6.2.4 Implementation The clinical evaluation of candidate vaccines for
dengue has several unique aspects, some of which are related to the above-mentioned challenges.
Dengue illness has many clinical manifestations and poses diagnostic challenges. Ideally, a
vaccine should be efficacious against all forms of dengue illness, ranging from febrile illnesses
to severe forms such as DHF and DSS. Trials need to be large enough to address a vaccine’s
impact on the different clinical forms of dengue. Phase 4, or post-marketing, trials will be
particularly important for dengue for the same reason. Likewise, longterm evaluation of
volunteers will be required to demonstrate lack of evidence for immune enhancement/severe
disease. Trials need to take place in multiple countries – particularly in both Asia and the
Americas – due to the distinct epidemiological characteristics and the viruses circulating in each
region. The greatest burden of disease is found in distinct age groups in different countries, and
the methodology of capturing clinical events may differ by age group and between countries.
The epidemic peak varies somewhat in timing and exact location from year to year even in
endemic countries; thus, long-term dengue surveillance data about the potential vaccine testing
141 Chapter 6. New avenues CHAPTER 6 site(s) is crucial and, even so, the unpredictability of
timing and location adds a level of complexity to calculations of trial sample size. To facilitate
the vaccine development process, WHO has developed guidelines for the clinical evaluation of
dengue vaccines (12). The Paediatric Dengue Vaccine Initiative (PDVI) supports the
establishment of field sites for the testing of vaccines. 6.2.5 Vaccine utilization for dengue
control Additional work is required to bring a vaccine from licensing to programmatic use in
dengue-endemic areas. Depending on cost-effectiveness and the outcome of financial and
operational analysis, countries may decide to introduce dengue vaccines into the national
immunization programmes for routine administration. If the vaccine is to be used for infants, the
dengue vaccination will need to be carried out on a schedule compatible with other vaccines.
Interference between dengue vaccine and other vaccines likely to be given in the same time
period must be ruled out. If the vaccine is to be delivered to older age groups, proper contact
points will need to be established to deliver the vaccine effectively and to ensure post-marketing

surveillance. In addition, vaccine presentation, packaging and stability requirements should be
compatible with large-scale use. WHO has produced generic guidelines to guide national
authorities in their decision-making on the introduction of new vaccines (13). To maximize the
effect of vaccination, the potential impact of a vaccine on dengue transmission needs to be
studied (e.g. the role of herd immunity). A number of modelling approaches are being taken to
address this and other similar issues, as well as the characteristics of the mosquito population
transmitting the virus and climatographic parameters. Given the complexity of dengue and
dengue vaccines, it is imperative to continue scientific research that is directed at improving our
understanding of the immune response in both natural DEN infections and vaccinees (e.g.
defining neutralizing and potentially enhancing epitopes, improving animal models) alongside
vaccine development and evaluation. 6.3 Dengue antiviral drugs 6.3.1 Overview The search for
dengue antivirals is a new endeavour that is gaining momentum due to both increased interest in
dengue and substantial progress in the structural biology of dengue virus. Furthermore, extensive
drug discovery efforts in HIV and HCV have taught us important lessons that encourage similar
strategies to be adopted for dengue. Since HCV and dengue virus are members of the
Flaviviridae family, the intensive work on HCV antivirals – especially those that target the RNA-
dependent RNA polymerase – can benefit the search for dengue antivirals (14). The rationale for
dengue antivirals arises from clinical studies that have noted that the quantity of virus circulating
in the blood of patients who develop DHF and DSS is higher by around 1–2 logs compared with
patients suffering from the milder dengue fever. Similar differences in viral load have been
observed in animal models of ADE (15,16,17). This observation suggests that progress to serious
dengue disease and adverse morbidity may be reversed by administering potent and safe small
molecule compounds that target essential steps in 142 Dengue: Guidelines for diagnosis,
treatment, prevention and control virus replication early during the disease, thereby lowering the
viral load substantially. This hypothesis requires field-testing when a suitable anti-dengue agent
is discovered. 6.3.2 Product development The life cycle of dengue virus readily shows that the
steps involved in virus entry, membrane fusion, RNA genome replication, assembly and ultimate
release from the infected cell can be targeted by small molecules (18). The importance of targets
such as the viral protease and polymerase have been studied by reverse genetics using infectious
clones to validate them as targets for drug discovery. On the basis of success in the HIV and
HCV fields in finding small molecules that target viral enzymes that are essential for virus

replication in infected cells, academic institutions and non-profit pharmaceutical enterprises and
consortia are progressing in their search for antiviral compounds active against these targets in
dengue virus. The field is also benefiting from new insights afforded by x-ray crystallography
and cryo-electron microscopy data. In the past five years alone, seven new 3-D structures of
dengue proteins have been solved and nine structures of other flavivirus proteins have become
available. Based on these, a number of in silico and high through-put screens have been and are
being undertaken, yielding several lead compounds so far (19). Currently the most advanced
targets are the NS3/NS2B protease and NS5 RNA-dependent RNA polymerase, which have
undergone high through-put screening and lead compound optimization. New targets – including
E, NS3 helicase, and NS5 methyltransferase – are being explored (20), and others will soon be
added to the list. Recent advances in understanding the mechanism of membrane fusion during
DEN infection of target cells has opened up new possibilities for designing novel antiviral
strategies that target the fusion step as well (21). Screening efforts are continuing and will
increase. They include the proprietary libraries of pharmaceutical and biotechnology companies,
focused libraries of compounds synthesized to specific targets (e.g. protease inhibitors), designed
libraries based on structural information, natural products and approved drugs. Different
approaches have been taken to screening compounds, such as high through-put screening of both
target protein activity and viral replication in cultured cells, high through-put docking in silico,
and fragment-based screening using NMR and x-ray crystallography. Distinct classes of
inhibitors are being explored, such as substrate- and transition-state-based as well as
nonsubstrate-based inhibitors. Reporter replicons based on yellow fever or DEN infectious
clones have facilitated screening in cell culture for both primary and secondary screens (22,23).
Early preclinical in vivo testing can be conducted in certain mouse models of dengue infection.
For instance, tissue and cellular tropism of DEN in AG129 mice (mice of the 129 background
lacking interferon a/b and g receptors) is similar to that in humans (24,25), and AG129 mice are
being used as the first step in preclinical testing of candidate antivirals (26). Alternative
approaches, such as interfering with viral replication using peptide-conjugated
phosphorodiamidate morpholino oligomers (P-PMOs), have also been proposed and are effective
in cell culture (27,28). Initial studies of such compounds in mice against the related West Nile
virus have been reported (29). Other nucleotide-based approaches, including RNAi
methodologies, have been investigated in the exploratory phase (30). In addition, cellular targets

Dengue fever

Recomendados

Recomendados

Más contenido relacionado

La actualidad más candente

La actualidad más candente (20)

Similar a Dengue fever

Similar a Dengue fever (20)

Último

Último (20)

Dengue fever