1793 Philadelphia yellow fever epidemic Philadelphia forced evacuation of certain neighborhoods and placed refugees in supervised camps. After the epidemic, the city inspected all houses and destroyed those it deemed unhealthy. American doctors did not identify the vector of yellow fever until the late nineteenth century. In 1881 Carlos Finlay, a Cuban doctor, argued that mosquito bites caused yellow fever; he credited Rush's published account of the 1793 epidemic for giving him the idea. He said that Rush had written: "Mosquitoes (the usual attendants of a sickly autumn) were uncommonly numerous..." In the late 1880s, Finlay's theories were confirmed in Cuba by experiments of the
Yellow fever disease from nonhuman primates to humans. The virus is thought to have originated in East or Central Africa and spread from there to West Africa. As it was endemic in Africa, the natives had developed some immunity to it. When an outbreak of yellow fever would occur in an African village where colonists resided, most Europeans died, while the native population usually suffered nonlethal symptoms resembling influenza. This phenomenon, in which certain populations develop immunity to yellow fever due to prolonged exposure in their childhood, is known as acquired immunity. The virus, as well as the vector "A. aegypti," were