2. Etiology
Dengue is a febrile illness caused by a flavivirus transmitted by
mosquitoes.
The principal vector is the mosquito Aedes aegypti, which breeds in
standing water
Aedes albopictus is a vector in some South-east Asian countries.
There are four serotypes of dengue virus, all producing a similar
clinical syndrome
3. Pathogenesis
Dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS)
occur in individuals who are immune to one dengue virus serotype and
are then infected with another. Prior immunity results in increased
uptake of virus by cells expressing the antibody Fc receptor and
increased T-cell activation with resultant cytokine release, causing
capillary leak and disseminated intravascular coagulation
• Endothelial damage also leads to hemorrhagic manifeststations
Hemorrhage is often widespread and associated with pleural effusion
and ascites. Focal hepatic necrosis,immune complex-mediated
glomerulonephritis, and transient bone marrow suppression may be
seen.
4. Clinical features of dengue fever
Incubation period is 2–7 days
Prodrome - 2 days of malaise and Headache
Acute onset - Fever, backache, arthralgias, headache, generalised
pains (‘break-bone fever’), pain on eye movement, lacrimation,
scleral injection, anorexia, nausea, vomiting, pharyngitis, upper
respiratory tract symptoms, relative bradycardia, prostration,
depression, hyperaesthesia, dysgeusia, lymphadenopathy
Fever - Continuous or ‘saddle-back’, with break on 4th or 5th day and
then recrudescence; usually lasts 7–8 days
5. Rash - Initial flushing faint macular rash in first 1–2 days.
Maculopapular, scarlet morbilliform blanching rash from days 3–5 on
trunk, spreading centrifugally and sparing palms and soles; onset
often with fever defervescence. May desquamate on resolution or give
rise to petechiae on extensor surfaces
Convalescence - Slow and may be associated with prolonged fatigue
syndrome, arthralgia or depression
Tourniquet test – In mild forms, petechiae occur in the arm when a
blood pressure cuff is inflated to a point between systolic and
diastolic blood pressure and left for 5 minutes (the positive
‘tourniquet test’) – a non-specific test of capillary fragility and
thrombocytopenia.
6. Complications
Dengue haemorrhagic fever and disseminated intravascular
coagulation
Dengue shock syndrome
Severe organ involvement
Vertical transmission if infection within 5 weeks of delivery
As the extent of capillary leak increases, DSS develops, with a raised
haematocrit, tachycardia and hypotension, pleural effusions and
ascites. This may progress to metabolic acidosis and multi-organ
failure, including acute respiratory distress syndrome (ARDS). Minor
(petechiae, ecchymoses, epistaxis) or major (gastrointestinal or
vaginal) haemorrhage, a feature of DHF, may occur. Cerebrovascular
bleeding may be a complication of severe dengue.
7. Diagnosis
Laboratory features include leucopenia, neutropenia
thrombocytopenia and elevated alanine aminotransferase (ALT) or
aspartate aminotransferase (AST)
Confirmation of diagnosis of dengue is established by the following:
Direct methods: Virus isolation by culture; genome detection by PCR;
NSl antigen detection.
Indirect methods: IgM detection; IgG detection.
8. Virus isolation or PCR requires the sample to be obtained within the
first 5 days of fever, is technically demanding, not universally
available and hence of limited practical use. NSl antigen is a highly
conserved glycoprotein of dengue virus and secreted during the initial
phase of illness. It disappears as antibodies appear and hence declines
as illness advances and in secondary dengue infections. The specificity
is -100% and sensitivity in the first 4 days of illness is 90% in primary
dengue and 70% in secondary dengue infection
Antibody determination needs careful interpretation. Following
primary dengue infection, 80% patients show detectable IgM
antibodies by day 5, 99% by day 10 that peak by day 14 and are
undetectable by 2-3 months. IgG antibodies rise later, peak to levels
lower than IgM, decline slowly and remain detectable at low levels for
life. Diagnosis of primary dengue infection is thus based on elevated
IgM antibodies.
9. Clinical Criteria for DF /DHF/DSS
Clinical Features of DF: An acute febrile illness of 2-7 days duration with two
or more of the following manifestations:
1. Headache,
2. retro-orbital pain,
3. myalgia,
4. arthralgia,
5. rash,
6. haemorrhagic manifestations.
10. DengueHaemorrhagic Fever (DHF):
A case with clinical criteria of dengue Fever plus
Haemorrhagic tendencies evidenced by one or more of the following :
1. Positive tourniquet test
2. Petechiae, ecchymoses or purpura
3. Bleeding from mucosa, gastrointestinal tract, injection sites or other
sites
Thrombocytopenia (<100 000 cells per cumm) plus
Evidence of plasma leakage due to increased vascular permeability,
manifested by one ormore of the following:
1. A rise in average haematocrit for age and sex >_ 20%
2. A more than 20% drop in haematocrit following volume replacement
treatment compared to baseline
3. Signs of plasma leakage (pleural effusion, ascites, hypoproteinemia)
12. Management
Management of dengue fever is symptomatic and supportive
Bed rest is advisable during the acute phase
Use cold/tepid sponging to keep temperature below 38.5 C.
Antipyretics may be used to lower the body temperature.
Aspirin/NSAIDS like Ibuprofen, etc should be avoided since it may
cause gastritis, vomiting, acidosis, platelet dysfunction and severe
bleeding. Paracetamol is preferable
Oral fluid and electrolyte therapy is recommended for patients with
excessive sweating or vomiting
Patients should be monitored for 24 to 48 hours after they become
afebrile for development of complications.
13. Chart 1. Volume replacement algorithm for
patients with DHF grades I & II
14. Chart 2. Volume replacement algorithm for patients
with DHF grade III
15. Chart 3. Volume replacement algorithm for patients
with DHF IV (DSS)
16. Indication of Platelet transfusion
1. Platelet count less than 10000/cu.mm in absence of bleeding
manifestations (Prophylactic platelet transfusion).
2. Haemorrhage with or without thrombocytopenia.
Dengue vaccine :
As of 2019, one version is commercially available, known
recombinant, live attenuated tetravalent dengue
vaccine (CYD-TDV) , and sold under the brand
name Dengvaxia. The vaccine is only recommended in
those who have previously had dengue fever or populations
in which most people have been previously infected.
