How is yellow fever transmitted?
Yellow fever is caused by the flavivirus. It is passed on by the bite of the Aedes aegypti mosquito. The cycle of infection involves the mosquito collecting the infection by biting an animal or human with the virus (the mosquito is unaffected; it merely carries the infection in its salivary glands). It will then pass on the virus to any subsequent animals or people that it bites. Once it has the virus, the mosquito remains a source of infection for the rest of its life. The virus is widespread among monkeys that live in the jungle canopy, and occasionally, a mosquito bite passes the disease on to a person, such as a forestry worker, who can then act as a source of infection when they return to their own community. While sylvatic (jungle) yellow fever can affect significna t numbers, the real risk is epidemics of urban yellow fever, when the the disease is carries back to town by a human reservoir of infection.
