In 2014 it was occurring in Florida in the continental United States but as of 2016 there were no further locally acquired cases. The disease was first identified in 1952 in Tanzania. The term is from the Kimakonde language and means "to become contorted". Signs and symptoms
Around 85% of people infected with Chikungunya virus experience symptoms, typically beginning with a sudden high fever above 39 °C (102 °F). The fever is soon followed by severe muscle and joint pain. Pain usually affects multiple joints in the arms and legs, and is symmetric – i.e. if one elbow is affected, the other is as well. People with Chikungunya also frequently experience headache, back pain, nausea, and fatigue. Around half of those affected develop a rash, with reddening and sometimes small bumps on the palms, foot soles, torso, and face. For some, the rash remains constrained to a small part of the body; for others, the rash can be extensive, covering more than 90% of the skin. Some people experience gastrointestinal issues, with abdominal pain and vomiting. Others experience eye problems, namely sensitivity to light, conjunctivitis, and pain behind the eye. This first set of symptoms – called the "acute phase" of Chikungunya – lasts around a week, after which most symptoms resolve on their own.Many people continue to have symptoms after the "acute phase" resolves, termed the "post-acute phase" for symptoms lasting three weeks to three months, and the "chronic stage" for symptoms lasting longer than three months.
The rate of molecular evolution was estimated to have a mean rate of 5 × 10−4 substitutions per site per year (95% higher probability density 2.9–7.9 × 10−4).Chikungunya is spread through bites from Aedes mosquitoes, and the species A. aegypti was identified as the most common vector, though the virus has recently been associated with many other species, including A. albopictus. Research by the Pasteur Institute in Paris has suggested Chikungunya virus strains in the 2005-2006 Reunion Island outbreak incurred a mutation that facilitated transmission by the Asian tiger mosquito (A. albopictus). Other species potentially able to transmit Chikungunya virus include Ae. furcifer-taylori, Ae. africanus, and Ae. luteocephalus. Mechanism
Chikungunya virus is passed to humans when a bite from an infected mosquito breaks the skin and introduces the virus into the body. The pathogenesis of chikungunya infection in humans is still poorly understood, despite recent outbreaks. It appears that in vitro, Chikungunya virus is able to replicate in human epithelial and endothelial cells, primary fibroblasts, and monocyte-derived macrophages. Viral replication is highly cytopathic, but susceptible to type-I and -II interferon. In vivo, in studies using living cells, chikungunya virus appears to replicate in fibroblasts, skeletal muscle progenitor cells, and myofibers.The type-1 interferon response seems to play an important role in the hosts response to chikungunya infection. Upon infection with chikungunya, the hosts fibroblasts produce type-1 alpha and beta interferon (IFN-α and IFN-β). In mouse studies, deficiencies in INF-1 in mice exposed to the virus cause increased morbidity and mortality.