Chikungunya virus particles. Transmission electron micrograph (TEM) of a section through numerous Chikungunya virus particles (virions, round). Each virion is composed of a central dense core surrounded by a viral envelope and is approximately 50 nanometres in diameter. The Chikungunya virus is transmitted by mosquitoes. It is the cause of Chikungunya disease, which causes joint pain and fever. There is no vaccine or treatment for the disease, which although often severe is rarely fatal.