This transmission electron micrograph (TEM) depicts numerous chikungunya virus particles, which are composed of a central dense core that is surrounded by a viral envelope. Each virion is approximately 50nm in diameter. Chikungunya virus is transmitted to people by mosquitoes. The most common symptoms of chikungunya virus infection are fever and joint pain. Other symptoms may include headache, muscle pain, joint swelling, or rash. Outbreaks have occurred in countries in Africa, Asia, Europe, and the Indian and Pacific Oceans. In late 2013, chikungunya virus was found for the first time in the Americas on islands in the Caribbean.