The most common way yellow fever is transmitted is through the bite of an infected mosquito.
In urban areas, yellow fever is primarily spread by the Aedes aegypti mosquito.
In forested areas, yellow fever is maintained in a cycle involving mosquitoes and non-human primates (such as monkeys).
This type of transmission occurs in rural areas where there is a mix of human and non-human primate populations.
yellow fever is endemic in tropical and subtropical areas of Africa and South America. People living in or traveling to these regions are at higher risk.