Overview
Chikungunya is a mosquito-borne viral disease caused by the chikungunya virus (CHIKV), an RNA virus in the alphavirus genus of the family Togaviridae. The name chikungunya derives from a word in the Kimakonde language, meaning “to become contorted”.
Distribution and outbreaks
CHIKV was first identified in the United Republic of Tanzania in 1952 and subsequently in other countries Africa and Asia (1). Urban outbreaks were first recorded in Thailand in 1967 and in India in the 1970s (2). Since 2004, outbreaks of CHIKV have become more frequent and widespread, caused partly due to viral adaptations allowing the virus to be spread more easily by Aedes albopictus mosquitoes. CHIKV has now been identified in over 110 countries in Asia, Africa, Europe and the Americas. Transmission has been interrupted on islands where a high proportion of the population is infected and then immune; however, transmission often persists in countries where large parts of the population have not yet been infected.
All regions with established populations of Aedes aegypti or Aedes albopictus mosquitoes have now experienced local mosquito-borne transmission.
Transmission
Chikungunya virus is transmitted by mosquitoes, most commonly Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus, which can also transmit dengue and Zika viruses. These mosquitoes bite primarily during daylight hours. They lay eggs in containers with standing water. Both species feed outdoors, and Ae. aegypti also feeds indoors.
When an uninfected mosquito feeds on a person who has CHIKV circulating in their blood, the mosquito can ingest the virus. The virus then replicates in the mosquito over several days, gets to its salivary glands, and can be transmitted into a new human host when the mosquito bites them. The virus again begins to replicate in this newly infected person and reaches high concentrations in their blood, at which point they can further infect other mosquitoes and perpetuate the transmission cycle.
Symptoms
In symptomatic patients, CHIKV disease onset is typically 4–8 days (range 2–12 days) after the bite of an infected mosquito. It is characterized by an abrupt onset of fever, frequently accompanied by severe joint pain. The joint pain is often debilitating and usually lasts for a few days but may be prolonged, lasting for weeks, months or even years. Other common signs and symptoms include joint swelling, muscle pain, headache, nausea, fatigue and rash. Since these symptoms overlap with other infections, including those with dengue and Zika viruses, cases can be misdiagnosed. In the absence of significant joint pain, symptoms in infected individuals are usually mild and the infection may go unrecognized.
Most patients recover fully from the infection; however, occasional cases of eye, heart, and neurological complications have been reported with CHIKV infections. Patients at extremes of the age spectrum are at higher risk for severe disease. Newborns infected during delivery and older people with underlying medical conditions may become severely ill and CHIKV infection can increase the risk of death.
Once an individual is recovered, available evidence suggests they are likely to be immune from future infections (4).
Diagnostics
Chikungunya virus may be detected directly in blood samples collected during the first week of illness using tests such as reverse transcriptase–polymerase chain reaction (RT–PCR).
Other tests can detect a person’s immune response to chikungunya virus infection. These are typically used after the first week of infection to test for antibodies to the virus. The antibody levels are typically detectable by the first week after illness onset and can still be detected for about 2 months.
Treatment and vaccines
The clinical management includes addressing fever and joint pain with anti-pyretics and optimal analgesics, drinking plenty of fluids and general rest. There is no specific antiviral drug treatment for CHIKV infections.
Paracetamol or acetaminophen are recommended for pain relief and reducing fever until dengue infections are ruled out, as non-steroidal anti-inflammatory drugs (NSAIDs) can increase the risk of bleeding.
While there are several vaccines currently in different stages of development (as of Dec 2022) they are yet to be licensed. There is no commercial vaccine available to protect against chikungunya virus infection.
Prevention and control
Prevention of infection by avoiding mosquito bites is the best protection. Patients suspected of having CHIKV infection should avoid getting mosquito bites during the first week of illness to prevent further transmission to mosquitoes, who may in turn infect other people.
The main method to reduce transmission of CHIKV is through control of the mosquito vectors. This requires mobilization of communities, who are critical in reducing mosquito breeding sites through emptying and cleaning containers that contain water on a weekly basis, disposing of waste, and supporting local mosquito control programmes.
During outbreaks, insecticides may be sprayed to kill flying adult mosquitoes, applied to surfaces in and around containers where the mosquitoes land, and used to treat water in containers to kill the immature larvae. This may also be performed by health authorities as an emergency measure to control the mosquito population.
For protection during outbreaks of chikungunya, clothing which minimizes skin exposure to the day-biting vectors is advised. Window and door screens should be used to prevent mosquitoes from entering homes. Repellents can be applied to exposed skin or to clothing in strict accordance with product label instructions. Repellents should contain DEET, IR3535 or icaridin.
Insecticide-treated mosquito nets should be used against day-biting mosquitoes by persons who sleep during the daytime, for example young children, sick patients or older people.
People travelling to areas of active CHIKV transmission should apply basic precautions including the use of insect repellents, wearing long sleeves and pants and ensuring rooms are fitted with screens to prevent mosquitoes from entering.
WHO response
WHO supports countries to conduct surveillance and control of arboviruses through the implementation of the Global Arbovirus Initiative.
WHO responds to chikungunya in the following ways:
- supporting countries in the confirmation of outbreaks through its collaborating network of laboratories;
- providing technical support and guidance to countries for the effective management of mosquito-borne disease outbreaks;
- reviews the development of new tools, including insecticide products and application technologies;
- formulating evidence-based strategies, policies and outbreak management plans;
- providing technical support and guidance to countries for the effective management of cases and outbreaks;
- supporting countries to improve their reporting systems;
- providing training on clinical management, diagnosis and vector control at the regional level with some of its collaborating centres;
- publishing guidelines and handbooks on epidemiological surveillance, laboratory, clinical case management and vector control for Member States; and
- advancing integrated multidisciplinary approaches across arboviral diseases through the implementation of the Global Arbovirus Initiative.
WHO encourages countries to develop and maintain the capacity to detect and confirm cases, manage patients and implement social communication strategies to reduce the presence of the mosquito vectors.
References
- Staples JE, Breiman RF, Powers AM. Chikungunya fever: an epidemiological review of a re-emerging infectious disease. Clin Infect Dis. 2009;49(6):942-948. doi:10.1086/605496
- Wimalasiri-Yapa BMCR, Stassen L, Huang X, et al. Chikungunya virus in Asia - Pacific: a systematic review. Emerg Microbes Infect. 2019;8(1):70-79. doi:10.1080/22221751.2018.1559708
- Russo G., et al., Chikungunya fever in Africa: a systematic review. Pathog Glob Health. 2020;114(3):136-144. doi:10.1080/20477724.2020.1748965
- Auerswald H, Boussioux C, In S, et al. Broad and long-lasting immune protection against various Chikungunya genotypes demonstrated by participants in a cross-sectional study in a Cambodian rural community. Emerg Microbes Infect. 2018;7(1):13.
- Pan American Health Organization Preparedness and Response for Chikungunya Virus: Introduction in the Americas Washington, D.C.