Chikungunya is an infection caused by the chikungunya virus. The most common symptoms are fever and joint pain, typically occurring four to eight days after the bite of an infected mosquito; however some people may be infected without showing any symptoms. Other symptoms may include headache, muscle pain, joint swelling, and a rash. Symptoms usually improve within a week; however, occasionally the joint pain may last for months or years. The very young, old, and those with other health problems are at risk of more severe disease.

The virus is spread between people by two species of mosquito in the Aedes genus: Aedes albopictus and Aedes aegypti, which mainly bite during the day, particularly around dawn and in the late afternoon. The virus may circulate within a number of animals, including birds and rodents. Diagnosis is done by testing the blood for either viral RNA or antibodies to the virus. The symptoms can be mistaken for those of dengue fever and Zika fever, which are spread by the same mosquitoes. It is believed most people become immune after a single infection.

The best means of prevention are overall mosquito control and the avoidance of bites in areas where the disease is common. This may be partly achieved by decreasing mosquitoes' access to water, as well as the use of insect repellent and mosquito nets. Chikungunya vaccines have been approved for use in the United States and in the European Union. No specific treatment for chikungunya is available; supportive care is recommended, with symptomatic treatment of fever and joint swelling.

The chikungunya virus is widespread in tropical and subtropical regions where warm climates and abundant populations of its mosquito vectors (A. aegypti and A. albopictus) facilitate its transmission. The disease was first identified in 1952 in Tanzania and named based on the Makonde words for "to become contorted". While the disease is endemic in Africa and Asia, outbreaks have been reported in Europe and the Americas since the 2000s. In 2014, more than a million suspected cases occurred globally. Chikungunya has become a global health concern due to its rapid geographic expansion, recurrent outbreaks, the lack of effective antiviral treatments, and potential to cause severe symptoms and death.

Chikungunya can be asymptomatic, with estimates of between 17% and 40% of infections showing no symptoms. For those experiencing symptoms, they typically begin with a sudden high fever above 39 °C (102 °F) around 3 to 7 days after the bite of an infected mosquito. The fever is often accompanied by severe muscle and joint pain, which affects multiple joints in the arms and legs and is often symmetric – i.e. if one elbow is affected, the other is as well. People with chikungunya also frequently experience headaches, 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.

For those with severe symptoms, approximately 30% to 40% continue to have symptoms after the "acute phase" resolves. The lasting symptoms tend to be joint pains: arthritis, tenosynovitis, and/or bursitis. If the affected person has pre-existing joint issues, these tend to worsen. Overuse of a joint can result in painful swelling, stiffness, nerve damage, and neuropathic pain. Typically the joint pain improves with time; however, the chronic stage can last anywhere from a few months to several years.

Almost all symptomatic cases feature joint pain, generally in more than one joint. Pain most commonly occurs in peripheral joints, such as the wrists, ankles, and joints of the hands and feet as well as some of the larger joints, typically the shoulders, elbows and knees. Joints are more likely to be affected if they have previously been damaged by disorders such as arthritis. Pain may also occur in the muscles or ligaments. In more than half of cases, normal activity is limited by significant fatigue and pain. Infrequently, inflammation of the eyes may occur in the form of iridocyclitis, or uveitis, and retinal lesions may occur. Temporary damage to the liver may occur.