In South America sporadic infections occur almost exclusively in forestry and agricultural workers who are exposed occupationally in or near forests. In Africa the virus is transmitted in the moist savanna zones of West Africa during the rainy season, and infections occur principally among children. At intervals, massive outbreaks resulting in thousands of cases develop in urban locations and villages in the dry savanna of Africa.
Yellow fever is a viral disease transmitted between humans by a mosquito.
General precautions to avoid mosquito bites should be followed. These include the use of insect repellent, protective clothing, and mosquito netting. Yellow fever is a very rare cause of illness in travelers, but most countries have regulations and requirements for yellow fever vaccination that must be met prior to entering the country. After immunization an International Certificate of Vaccination is issued and will meet entry requirements for all persons traveling to or arriving from countries where there is active or a potential for yellow fever transmission. The Certificate is good for 10 years.