Yellow fever the introduction of sugar plantations created the conditions for mosquito and viral reproduction, and subsequent outbreaks of yellow fever. Deforestation reduced populations of insectivorous birds and other creatures that fed on mosquitoes and their eggs. Although yellow fever is most prevalent in tropical-like climates, the northern United States were not exempted from the fever. The first outbreak in English-speaking North America occurred in New York City in 1668, and a serious one afflicted Philadelphia in 1793. English colonists in Philadelphia and the French in the Mississippi River Valley recorded major outbreaks in 1669, as well as those occurring later in
Yellow fever on the African continent. In 2008, the largest number of recorded cases was in Togo. In 2016, a large outbreak originated in Angola and spread to neighboring countries before being contained by a massive vaccination campaign. In March and April, 11 cases were reported in China, the first appearance of the disease in Asia in recorded history. Phylogenetic analysis has identified seven genotypes of yellow fever viruses, and they are assumed to be differently adapted to humans and to the vector "A. aegypti". Five genotypes (Angola, Central/East Africa, East Africa, West Africa I, and West Africa II) occur only in