Causative Agent
- Yellow Fever Virus (YFV)
Incubation Period
- 3 - 6 days
Infectious Period
- Initial 5 days of illness.
Transmission
Vector-borne transmission occurs via bite of an infected mosquito, primarily Aedes or Haemogogus spp. Nonhuman and human primates are the main reservoirs of the virus; anthroponotic (human-to-vector-to-human) transmission occurs.
Three main transmission cycles:
- The sylvatic (jungle) cycle involves transmission of the virus between non- human primates and mosquito species found in the forest canopy and subsequent transmission to humans when they encroach into the jungle during occupational and recreational activities.
- The intermediate (savannah) cycle in Africa involves transmission of YFV from monkeys to hole-breeding Aedes spp to humans working or living in jungle border areas.
- The urban cycle involves transmission of the virus between humans and urban mosquitoes, primarily Ae. aegypti.
Humans infected by YFV experience high levels of viraemia making blood-borne transmission possible (via transfusion, needle stick, and intravenous drug abuse)
Epidemiology
Yellow fever occurs in sub-Saharan Africa and tropical South America, where it is endemic with intermittent epidemics. In Africa, natural immunity increases with age, thus infants and children are at greatest risk for disease.
The incidence world-wide has increased due to recurrent epidemics in several West African cities.
- Leucopoenia, thrombocytopenia
- Elevated direct bilirubin, transaminases, urea, creatinine
- Hypoglycaemia
- Specific diagnosis by:
- viral isolation from blood or tissue specimens.
- identification of viral antigen or nucleic acid in tissues (including liver) using immunohistochemistry (IHC), enzyme-linked immunosorbent assay (ELISA) antigen capture, or polymerase chain reaction tests.
- serological diagnosis by IgM antibody capture (ELISA), histo-immunochemistry or complement fixation tests (CFT).
Locally, a complement fixation test to the flaviviruses group can be done. =
Positive results in the appropriate clinical setting may be suggestive but =
not confirmatory.<br>
- Suspected patients will be isolated at CDC. Treatment is symptomatic and supportive and directed at the management of the complications of YF.
- There is no specific anti-viral therapy.
