1. Dr KAMRAN AFZAL
Asst Prof Microbiology

2. Dengue Virus
 Genus: Flavivirus
 Family: Flaviviridae
 Single-stranded RNA arbovirus
 40–50 nm, spherical, lipid env
 Genome is approximately 11 Kb
 4 serotypes:
 DEN-1, DEN-2, DEN-3 and DEN-4
 Infection with one dengue serotype provides lifelong immunity
to that serotype, but there is no cross-protective immunity to
the other serotypes

3. Dengue Virus Particles

4. Aedes aegypti

5. Aedes Mosquito - Characteristics
Distinct physical feature
Black and white stripes
on its body and legs
Flying time: dusk to dawn
Bites during the day
Short flight: house to house
Imperceptible bite

6.  Lays its eggs in clean, stagnant water
 Pots, pans and utensils

7. Life cycle of Aedes aegypti
4. Adult
3. Pupae 1. Eggs
2. Larvae

8. Did you know…
 The female mosquito lays 30–150 eggs every 2-3 days
 Only the female Aedes mosquitoes feed on blood
 Female mosquitoes need the protein found in blood to produce eggs
 Human blood is preferred with the ankle area as a favored feeding
site
 Male mosquitoes feed on plant and fruit nectar
 After 8-12 days of acquiring the virus, mosquitoes become
infective, remain so for whole life span (1-3 months)
 The eggs of A. aegypti can resist desiccation for up to 1 yr

9. Epidemiology
 Endemic in more than 100 countries
 A leading cause of hospitalization and death among
children in Asia
 2.5 billion people or two fifths of the world population
are now at risk
 50 million cases of DF worldwide every year
 0.5 million cases of DHF require hospitalization each
year, a very large proportion of whom are children,
~ 5% die
 Without proper treatment, DHF fatality rates can
exceed 20%

10. Worldwide Prevalence

11. World at Risk

12. Worldwide Resurgence

13. Transmission Cycle
 Transmission from human to human requires
the same female mosquito to bite a viremic
human and then bite a susceptible human at
an interval of around 8-12 days

14. Pathogenesis of DHF - 1
 Homologous Antibodies form non-infectious complexes

15. Pathogenesis of DHF - 2
 Heterologous Antibodies form infectious complexes

16. Pathogenesis of DHF - 3
 Heterologous complexes enter monocytes, where
virus replicates

17. Pathogenesis of DHF - 4
 Infected monocytes → vasoactive
mediators → increased vascular
permeability and hemorrhagic
manifestations (DHF and DSS)
 Activation of memory T cells →
Inflammatory cytokines, including TNF-α
and interleukins (IL-2, IL-6, and IL-8) →
Increased vascular endothelial permeability
or trigger death of target cells through
apoptosis

18. Pathology of DHF and DSS - 1
DF
 Rash in DF show a lymphocytic vasculitis in the dermis
DHF and DSS
 Most of the morphologic abnormalities result from DIC
and shock
 Hemorrhage and congestion are seen in many organs
 Hemorrhagic effusions in the pleural, pericardial and
abdominal cavities

19. Pathology of DHF and DSS - 2
 Liver and spleen are the target organs
 DEN virus antigen detected in hepatocytes
 Liver - Variable morphology
 Severe, diffuse hepatitis with mid-zonal necrosis
 Focal areas of necrosis
 No PMN cells, and no lymphocytes in the liver lesions
 Kupffer cells destroyed in cases of focal or severe necrosis
 Councilman hyaline body is present as an apoptotic cell

20. • Spleen - Enlarged and hemorrhagic

21. Dengue Clinical Syndromes
 Classic dengue fever (DF)
 Dengue hemorrhagic fever (DHF)
 Dengue shock syndrome (DSS)
 DSS is actually a severe form of DHF

22. Case Definition: Dengue Fever
 An acute febrile viral disease frequently presenting with
headaches, bone or joint pain, muscular pains, rash and
thrombocytopenia (Breakbone fever)
 Incubation period
 3-7 days (range 2-15 days)
 Temperature
 Bimodal peak (saddle-back form)
 Rash
 Maculo-papular, lasts for 3-4 days

23. Case Definition: DHF
4-Necessary Criteria (W.H.O.)
 Fever, or recent history of acute fever
 Hemorrhagic manifestations
 Low platelet count (100,000/mm3 or less)
 Objective evidence of “leaky capillaries”:
 Elevated hematocrit (20% or more over baseline)
 A positive ‘Tourniquet Test’
 Pleural or other effusions

24. Case Definition: DSS
 4-N criteria for DHF
+
 Evidence of circulatory failure
 Rapid and weak pulse
 Narrow pulse pressure (< 20 mm Hg) OR
hypotension for age
 Cold, clammy skin and altered mental status
 Frank shock is direct evidence of circulatory failure
 DEN-2
 Mortality rate 1-10% (up to 40%)

25. Hemorrhagic Manifestations
 Skin hemorrhages
 Petechiae, purpura, ecchymoses
 Gingival bleeding
 Nasal bleeding
 Gastrointestinal bleeding
 Hematemesis, melena
 Hematuria
 Increased menstrual flow

26. Tourniquet Test
 Inflate blood pressure cuff to
a point midway between
systolic and diastolic pressure
for 5 minutes
 Positive test:
 20 or more petechiae per 1 inch²
(6.25 cm²)

27. Differential Diagnosis
 Influenza
 Measles
 Rubella
 Malaria
 Typhoid fever
 Leptospirosis
 Meningococcemia
 Rickettsial infections
 Bacterial sepsis
 Other viral hemorrhagic fevers

28. Common Misconceptions - DHF
 Dengue fever + bleeding = DHF
 Apply 4 WHO criteria and assess capillary permeability
 DHF kills only by haemorrhage
 Patient dies as a result of shock
 Poor management turns dengue into DHF
 Poorly managed dengue can be more severe, but DHF is a
distinct condition, which even well-treated patients may develop
 Positive tourniquet test = DHF
 Tourniquet test is a nonspecific indicator of capillary fragility

29. Treatment
 Monitor blood pressure, hematocrit, platelet
count, level of consciousness and urine output
 Fluids
 The volume of fluid needed is similar to the treatment
of diarrhea with mild to moderate isotonic dehydration
 Antipyretics
 Avoid aspirin and NSAIDS
 Blood and components therapy
 Continue monitoring after defervescence
 Patients develop DHF after defervescence

30. Laboratory Diagnosis
 Non-specific lab tests
 CBC - WBCs, platelets, hematocrit
 Urine - check for microscopic hematuria
 Dengue-specific lab tests
 Serology
 IgM ELISA / ICT
 IgG ELISA / ICT
 NS1 Antigen ELISA / ICT
 Virus isolation
 PCR to determine serotype
 Cell culture
 Mosquito Inoculation

31. ELISA Test for Serologic Diagnosis

32. Virus Isolation: Cell Culture/
Fluorescent Antibody Test

33. Virus Isolation: Mosquito Inoculation

34. Prevention and Control

35. Mosquito Repellants
 Insecticide sprays
 Knock down and residual
 Repellant oils
 Repellant lotions
 Electric lamps
 Mats
 Coils
 High frequency sound
 Use a larvicide
 Temephos

36. Mosquito Barriers
 Keep patient in screened sickroom or
under a mosquito net
 To prevent Aedes aegypti mosquitoes
from biting infected patients and
acquiring the virus

37. Outdoor Fogging

38. Indoor Fogging

39. Aerial Spraying

40. Media Campaigns

41. Health Ministry Campaign

42. CDC Handout

43. CDC Investigation Report

44. Dengue Vaccine?
 No licensed vaccine at present
 Effective vaccine must be ‘tetravalent’
 Clinical trials of an attenuated tetravalent
vaccine currently underway
 Effective, safe and affordable vaccine will not
be available in the immediate future

45. Role of Pak Army in Dengue

46. Role of Pak Army in Dengue

47. Future Outlook
 Continued vigilance and surveillance is very important
 True and active community participation is the key
 It is likely to be few years before the vaccine can be
considered for widespread use in populations in endemic
areas
 The only control method is:
‘ Efficient vector control ’

48. Aedes aegypti
Thank you