Yellow Fever

Yellow Fever

Yellow fever is found only in parts of Central and South America and Sub-saharan Africa (see Yellow Fever Risk Areas).

The cause is a virus that is spread through the bite of an infected Aedes aegypti mosquito which predominantly bites during daylight hours. It exists in three transmission cycles; Jungle, Urban and Intermediate yellow fever. 

Jungle yellow fever - is transmitted among non-human hosts (mainly monkeys) via forest mosquitoes. Humans can become infected when they enter the forest habitat and can become the source of urban yellow fever outbreaks 

Urban yellow fever - is spread to urban areas by mosquitoes, mainly Aedes aegypti, that have bitten monkeys or humans infected with yellow fever. Urban yellow fever can occur in areas populated by man that are in close proximity to forests where infected monkeys and the mosquito vector can be found.

Both jungle and urban cases occur in Africa (especially west Africa). Urban cases are rare in the Americas. 

Intermediate yellow fever - occurs only in Africa in humid savannah regions where mosquitoes infected both monkeys and humans causing localised outbreaks.  

Yellow Fever - The Illness

The incubation period is usually short, 3-6 days. Symptoms of the disease include sudden onset of fever, backache, generalised muscle pain, nausea and vomiting. Jaundice can also be seen early in the disease and this intensifies as the disease progresses. Infection with yellow fever results in lifelong protection in individuals who survive. Up to 60% of those infected with yellow fever will die from the disease.


There is no specific treatment for yellow fever virus.

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