Chikungunya is a mosquito-borne alphavirus of the Togaviridae family endemic in sub-Saharan Africa, Southeast Asia, Indonesia, the Philippines, India, and the Americas. The World Health Organization (WHO) recognizes chikungunya as a neglected tropical disease (NTD) because of its substantial impact on affected populations, particularly in tropical and subtropical regions. Since the first documented local transmission in the Caribbean in 2013, widespread outbreaks have occurred throughout the Caribbean, Central America, and parts of South America.

The virus is transmitted primarily through the bite of infected mosquitoes, primarily Aedes aegypti and Aedes albopictus (which can also transmit dengue fever). Natural reservoirs include humans, primates, other mammals, and birds, but humans are the primary amplifying host (ie, humans can infect mosquitoes that bite them during the first week of illness). Person-to-person transmission of chikungunya has not been documented, although there have been reports of vertical transmission in the perinatal period in birthing parents with acute infection, with subsequent high levels of morbidity for the neonate. There is no evidence supporting transmission through breastfeeding.

The typical clinical presentation is fever and joint pain with many, but not all, patients developing a rash. Following an incubation period of 1-14 days (most commonly 3-7 days), there is abrupt onset of a high fever accompanied by severe polyarthralgia. The fever is classically biphasic, resolving after a few days, only to return again after a few days of being fever free. The arthralgias are usually symmetrical, migratory, and involve the small joints of the hands, wrists, ankles, and feet. Additional symptoms may include chills, myalgias, headache, retro-orbital pain, and photophobia. Joint symptoms may persist for weeks to months after the acute illness has resolved.

Disease severity varies considerably. According to the US Centers for Disease Control and Prevention (CDC), approximately 3%-28% of infected individuals remain asymptomatic. While most symptomatic infections are self-limited, severe disease has been reported during multiple outbreaks. In a 2016 study of 110 nonpregnant adults hospitalized with chikungunya virus infection in Guadeloupe, 42 patients developed severe disease characterized by a syndrome resembling severe sepsis or septic shock. Severe illness and death were also reported during other outbreaks, including on Reunion Island.

Although uncommon, atypical manifestations may occur and can involve multiple organ systems. Reported neurologic complications include encephalitis, meningoencephalitis, myelitis, Guillain-Barré syndrome, optic neuritis, and myeloradiculitis. Cardiac and renal manifestations such as myocarditis, acute kidney injury, and acute interstitial nephritis have also been described. Ocular complications may include uveitis, anterior uveitis, and retinitis. Rarely, mucosal or gastrointestinal hemorrhage may occur, with mucosal involvement being more common in children.

Neonates, older adults, and individuals with underlying medical conditions, including hypertension, diabetes (type 1, type 2), and cardiovascular disease, are at increased risk for severe or atypical disease manifestations.

Travelers to endemic areas are at higher risk for contracting chikungunya. In 2014, over 1600 travel-associated cases were reported throughout the United States, resulting in 11 locally transmitted cases (all in Florida). Since then, local transmission was also identified in Texas, Puerto Rico, and the US Virgin Islands.