L47 Arbovirus Flashcards
Human as the amplifying host what does it mean? - relies on? - asymptomatic ratio? Example?
- other animal species are not involved in the transmission cycle
- relies on high human and vector population density (e.g. urban settings) > thus vector control as prevention
- high asymptomatic ratio
Dengue
Human as the accidental host
Example?
- meaning?
- case-fatality ratio?
Japanese encephalitis virus
- human not involved in normal cycle
- high case-fatality ratio
What are the non-specific febrile illness for vector borne viral infections?
e.g. Dengue, Chikungunya, Zika
Prognosis: usually self-limiting
- Biphasic fever: 2nd phase due to immune-mediated factors
- Pain: frontal headache, ortbital, back, bone, joint
- Skin rash
- Dyscrasia: WBC reduced (c.f. bacterial infection), severe thrombocytopenia (reduced platelets)
Hemorrhage and shock can be caused by what virus?
Dengue virus
What vector borne virus causes hepatitis?
Yellow fever
JEV usually causes which type of encephalitis?
What symptoms?
Pan-encephalitis
- vomiting, convulsion, generalised seizures
How to diagnose vector borne virus infections?
- Clinical
- Serology
- CSF for IgG and PCR
What antiviral can be used to treat arboviruses?
Side effect?
Ribavirin
- useful for a broad spectrum of virus (DNA and RNA)
- only antiviral used for arboviruses
e. g. hemorrhagic fever
S/E: hemolysis
Vaccination is available in which arbovirus infection? (4)
- Yellow fever
- Dengue (but not useful)
- Japanese encephalitis
- TBE
Which of the following about Dengue virus is incorrect?
A. Most cases in HK are imported
B. MC in September
C. Human as amplifying host
D. It favours high temperatures
E. It is domesticated and lay eggs in clean water
F. Only female transmit infections
D
- favours low temperature - active in early morning and late afternoon
F: because females take blood for producing eggs
What is the vectors for Dengue? (2)
Which is more common in HK?
Aedes aegypti - primary, more efficient in spreading infections
Aedes albopictus - secondary, more common in HK
Dengue virus
- Enveloped/non-enveloped?
- ss/ds RNA/DNA?
- family?
- serotypes?
What is the significance of knowing the serotypes?
Enveloped ssRNA in Flaviviridae
4 Serotypes: DEN-1, -2, -3, -4
*no cross-protection, need to be immune to all 4 serotypes for true immunity
Patients can be asymptomatic in dengue fever.
If symptomatic, how can it present? (3)
- Undifferentiated fever - non-specific febrile illness with rash
- Dengue fever - with/without hemorrhage (Classic)
- Dengue hemorrhagic fever - with shock/ Dengue Shock syndrome (DSS)
For dengue hemorrhagic fever, febrile phase: biphasic fever.
Plasma leak phase?
Normal/subnormal temperature: serous effusion > shock (dengue shock syndrome DSS)
- Trigger cytokine release from macrophage
> increase permeability of blood vessels > hemorrhage > shock
Then reabsorption phase: resolution of hemorrhage…
What is antibody-dependent enhancement in Dengue?
What is it related to DHF/DSS?
- Infection with 1 of the 4 DENV serotypes generates long-term homotypic immunity (one only), but also generates some heterotypic (cross-reactive) and non-neutralizing Ab
- Subsequent infection with heterotypic DENV > these non-neutralising Ab bind to DENV > failure to clear the virus > virus replicates in the macrophages
- 100x increase in viremia + cytokine storm by macrophages
- Dengue hemorrhage fever/ Dengue Shock Syndrome
