Three transmission cycles for yellow fever have been identified. Sylvatic (jungle) transmission and urban transmission. The third type of transmission, called intermediate, it is a combination of sylvatic and urban transmission. Sylvatic transmission usually involves the spread of the virus from primate to primate. It can, however, spread from primate to human. This happens when humans accidentally become involved in the cycle. Urban transmission affects mainly humans. The Aedes aegypti mosquito, which lives among human populations, is the main vector in urban transmission. When infected humans introduce the virus into urban areas with large numbers of unvaccinated individuals, infected mosquitoes transmit the disease from human to human. This
