Yellow fever cycle, both in Africa and South America, a sylvatic cycle (forest or jungle cycle) is present, where "Aedes africanus" (in Africa) or mosquitoes of the genus "Haemagogus" and "Sabethes" (in South America) serve as vectors. In the jungle, the mosquitoes infect mainly nonhuman primates; the disease is mostly asymptomatic in African primates. In South America, the sylvatic cycle is currently the only way humans can become infected, which explains the low incidence of yellow fever cases on the continent. People who become infected in the jungle can carry the virus to urban areas, where "A. aegypti" acts as a vector.
Yellow fever vaccine It should not be given to those with very poor immune function. Yellow fever vaccine came into use in 1938. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale price in the developing world is between US$4.30 and US$21.30 per dose as of 2014. In the United States it costs between US$50 and US$100. The vaccine is made from weakened yellow fever virus. Some countries require a yellow fever vaccination certificate before entry from a country where the disease is common. People most at risk