Outbreaks of the chikungunya virus occurred primarily in Africa, Asia, the Americas, and the Indian and Pacific oceans. In 2013, the virus was identified in local transmission in the Caribbean countries and territories. It has since spread throughout the Americas, where 1.7 million cases have been reported. Locally acquired cases have not been reported in the US since 2019.
The greatest risk is from travelers who visit areas with ongoing epidemics spreading the virus to new areas. The mosquitoes that carry the virus are the same ones that spread dengue and Zika viruses—Aedes aegypti and Ae. albopictus. Because those people who are infected have a high viral load, local transmission is possible wherever the mosquitoes live. Most epidemics occur in tropical areas in the rainy season, but they can also occur less frequently in drought conditions.
