Chikungunya virus belongs to the family Togaviridae, genus Alphavirus. Alphavirus infections can either cause arthralgic or neuroinvasive disease. Other medically important alphaviruses found in the Americas include eastern equine encephalitis virus (neuroinvasive) and Mayaro virus (arthalgic). Chikungunya virus has a single-stranded, positive-sense RNA genome. The virus particles are enveloped icosahedral capsids and have a diameter of 60-70 nm.