Yellow fever is a tropical disease that is spread to humans by infected mosquitoes, and although most infections are mild, the disease can be severe and life threatening (Yellow pp). Found in Africa and South America, yellow fever is preventable by immunization and travelers to those countries are advised to get the vaccine (Yellow pp). In South America sporadic infections occur mostly in forestry and agricultural workers from occupational exposure in or near forests (Yellow-1 pp). .

             There are two kinds of yellow fever which are spread by two different cycles of infection (Yellow pp). Jungle yellow fever is mainly a disease of monkeys that is spread from infected mosquitoes to monkeys in the tropical rain forest (Yellow pp). It is then spread to people who are bitten by mosquitoes that have been infected by monkeys (Yellow pp). Jungle yellow fever is rare and usually occurs in persons who work in tropical rain forests (Yellow pp). Urban yellow fever is a disease of humans and is spread by mosquitoes that have been infected by other people, usually by the aedes aegypti mosquito (Yellow pp). .

             These mosquitoes have adapted to living among humans in cities, towns, and villages and are known to breed in discarded tires, flower pots, oil drums, and water storage containers close to human dwellings (Yellow pp). It was Walter Reed and his assistants James Carroll, Aristides Agramonte, and Jesse Jazear, while at experimental stations outside Havana, Cuba that proved the Aedes aegypti mosquito was the "vector" for the yellow fever virus (Yellow-3 pp). This work destroyed the popular myth that yellow fever was spread by direct contact with infected people or "contaminated" objects and thus, focused efforts on the eradication of the Aedes mosquito (Yellow-3 pp). Urban yellow fever is the cause of most yellow fever outbreaks and epidemics (Yellow pp).

             Although a disease of the tropics, from 1793-1822, yellow fever was one of the most dreaded diseases in the port cities of the United States (Rush pp).