Yellow fever virus (YFV) is the prototype member of the genus Flavivirus, a 
group of viruses that are transmitted between vertebrates by arthropod vectors. 
The virus is found in tropical regions of Africa and South America and is 
transmitted to primates by mosquitoes: Aedes spp. in Africa and Haemagogus and 
Sabethes spp. in South America. Despite the availability of an effective 
vaccine, yellow fever (YF) is considered a reemerging disease owing to its 
increased incidence in the past 25 years. Molecular epidemiologic data suggest 
there are seven genotypes of YFV that are geographically separated, and 
outbreaks of disease are more associated with particular genotypes. In addition, 
the risk of urban YF, owing to transmission of the virus by Aedes aegypti, is 
increasing in Africa, as is the potential of urban YF returning to South 
America. Both present serious potential public health problems to large 
population centers.