Yellow Fever Virus
Transmission of the yellow fever virus occurs in two main ways: urban (a mosquito bites an infected human) and sylvatic (mosquito bites an infected monkey).
Urban yellow fever virus transmission occurs when a mosquito bites an infected human. Once infected, this mosquito can then bite and infect another human. The infected mosquito can continue to pass along the yellow fever virus for its entire life. Aedes aegypti is the type of mosquito that normally transmits this urban type of yellow fever. This type of yellow fever virus transmission can lead to an epidemic of yellow fever disease. For example, in Brazil in 1973, at least 21,000 individuals out of 1.5 million people became infected with the yellow fever virus.
Sylvatic yellow fever virus transmission occurs when a mosquito bites an infected monkey. Once infected, this mosquito will usually bite other monkeys; however, in certain cases, this mosquito can bite humans. This type of yellow fever virus transmission is more sporadic and usually only occurs in people that work within tropical rain forests. In East Africa, this mode of yellow fever transmission occurs through the forest canopy mosquito, A. africanus, which seldom feeds on humans.
(Click Transmission of the Yellow Fever Virus for more information.)