Chikungunya Virus in Thailand; An Update

Chikungunya virus (CHIKV) is an emerging or re-emerging mosquito borne virus that can be found in several countries in Africa and Asia. Belonging to Alphavirus genus of the Togaviridae family, CHIKV is an enveloped, single-stranded, positive-sense RNA virus. It was first discovered in Tanzania, east Africa in 1952 and was identified in Thailand in 1958. There are four distinct lineages of CHIKV based on the E1 envelope glycoprotein sequences: the West African lineage, the East Central and South African (ECSA) lineage, the Asian lineage, and the Indian Ocean lineage (IOL). IOL is a new lineage that evolved from the ECSA lineage, which first emerged in Kenya in 2004 and spread to Indian Ocean Islands, India, and Southeast Asia (Parola et al., 2006). However, no evidence indicates the virulence difference among CHIKV lineages. Transmission cycle of CHIKV involves Aedes mosquito vectors, humans, and possibly mammal reservoir hosts (Jupp and McIntosh, 1990; Turell et al., 1992). Transovarial transmission of CHIKV was also indicated in Aedes mosquitoes (Thavara et al., 2009).