The Travels of Chikungunya
The chikungunya virus, an alphavirus of family Togaviridae, was originally isolated in Tanzania in 1953. The virus circulates among monkey populations in the forests of that country. It is transmitted by mosquitoes of the genus Aedes, particularly Aedes aegyptii (which is widely distributed in the Americas today) and Aedes albopictus. Nosocomial transmission of chikungunya by needle stick has been reported.
Chikungunya received relatively little attention until a recent series of explosive outbreaks began in African coastal cities in 2004, and afterward in islands in the Indian Ocean, in mainland India, elsewhere in Asia (most recently, in Thailand and Malaysia), and in Italy (Figure WO-7). There have been thousands of chikungunya infections in travelers, most notably an Indian man whose visit to family members in Castaglione, Italy, in 2007, ignited a localized outbreak of chickungunya fever. The vector in this case was Ae. albopictus, which was introduced to Italy in used tires imported from the United States, which in turn received the species in used tires imported from Japan.
Symptoms of chikungunya infection include rash, myalgia,a headache, arthralgiab (which tends to be severe, incapacitating, and persistent), and fever. The virus has a high attack rate, so it can disable entire populations upon its introduction. An apparently recent mutation in the chikungunya virus improved its efficiency of transmission by Ae. albopictus; this may explain the explosiveness of recent outbreaks (Tsetsarkin et al., 2007).
Although many cases of chikungunya have been imported to the Americas, to date none of these have resulted in transmission. However, a recent study found that Ae. aegyptii and albopictus strains present in the United States could be infected with, and could subsequently transmit, recent outbreak strains of the virus (Reiskind et al., 2008; Vazeille et al., 2007).