Dark green denotes countries with current or previous local transmission of CHIKV, per CDC as of Sept 17, 2019.<unk>  is a mosquito-borne alpha virus that was first isolated after a 1952 outbreak in modern-day Tanzania. The virus has circulated in forested regions of sub-Saharan African in cycles involving nonhuman primate hosts and arboreal mosquito vectors. Phylogenetic studies indicate that the urban transmission cycle—the transmission of a pathogen between humans and mosquitoes that exist in urban environments—was established on multiple occasions from strains occurring on the eastern half of Africa in non-human primate hosts. This emergence and spread beyond Africa may have started as early as the 18th century. Currently, available data does not indicate whether the introduction of<unk>  into Asia occurred in the 19th century or more recently, but this epidemic Asian strain causes outbreaks in India and continues to circulate in Southeast Asia. A number of<unk>  outbreaks have occurred since 2005. An analysis of the<unk>  virus's genetic code suggests that the increased severity of the 2005–present outbreak may be due to a change in the genetic sequence, altering the virus' viral coat protein, which potentially allows it to multiply more easily in mosquito cells. The change allows the virus to use the Asian tiger mosquito (an invasive species) as a vector in addition to the more strictly tropical main vector, Aedes aegypti. In July 2006, a team analyzed the virus' RNA and determined the genetic changes that have occurred in various strains of the virus and identified those genetic sequences which led to the increased virulence of recent strains.
Epidemiology of chikungunya
Epidemiology of measles
Epidemiology of syphilis
Epidemiology of bed bugs
Epidemiology of snakebites
Lyme disease microbiology
Epidemiology of herpes simplex
Epidemiology of HIV/AIDS