A mosquito-borne virus of the family Flaviviridae

Mosquitos, especially Aedes aegypti.

Yellow fever is an acute infectious disease that presents a major public health threat in endemic zones of Africa, where the virus continues to reappear even after long periods of quiescence.

The agent which causes yellow fever is a mosquito-borne virus of the family Flaviviridae. It is maintained in a transmission cycle involving forest-dwelling mosquitos and non-human primates, often referred to as the "jungle" cycle. Occasionally, humans acquire yellow fever in the jungle and then move to a village or urban area where they may be fed upon by domestic species of mosquitos, especially Aedes aegypti, which is also a carrier of the virus. This may trigger "urban" yellow fever, with potentially devastating effects. Many major cities of Africa are infested with Aedes aegypti mosquitos, and thousands of deaths could rapidly ensue from the introduction of yellow fever before a vaccination campaign could have any effect.

Yellow fever is characterized by sudden onset of fever, chills, headache, backache, generalized muscle pain, prostration, nausea and vomiting. Leucopenia appears early, possibly together with haemorrhagic symptoms. Jaundice is moderate early and intensifies later. As the disease progresses there is slowed and weakened pulse, albuminuria and at times anuria.

The incidence of yellow fever is greatest in recognized endemic/enzoonotic regions of West Africa, especially Liberia, Ghana, Nigeria and adjacent countries. Several hundred to a few thousand cases are reported annually. Rural populations are at greatest risk, with most adult cases occurring among young adult males who enter forests as part of their work. Male cases normally outnumber female by a ratio of about 2:1.

Vaccination, both as a matter of routine through established EPI programmes as well as through emergency mass vaccination campaigns in the event a yellow fever outbreak is reported; vector control, meaning reduction of the A. aegypti population, by organizing local community clean-up campaigns to eliminate their breeding sites; and isolation of yellow fever patients in mosquito-proof rooms to prevent further spread of the virus into the mosquito population.


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