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Chikungunya
This page provides some facts about chikungunya. There have been a number of recent outbreaks however, no outbreaks have been recorded in Australia.
Background
Chikungunya, a viral disease (CHIKV), is transmitted to humans by infected mosquitoes, typically Aedes aegypti, although there may be other competent mosquito vectors. The name, chikungunya, comes from the Makonde word (one of the local languages in Tanzania) for stooped walk, reflecting the physique of a person suffering from the disease. The disease has been described in Africa, South-East Asia, southern India and Pakistan. It occurs principally during the rainy season. CHIKV is an alphavirus of the family of Togaviridae and is related to Ross River virus (RRV), Barmah Forest virus (BFV) and Sindbis virus.Identification
Clinical Features
Chikungunya causes illness characterised by an abrupt onset of fever, headache, rash and severe joint pain in approximately 70% of cases. The acute disease lasts 3 to 10 days, but convalescence may include prolonged joint swelling and pain lasting weeks or months. Symptoms appear between 3 and 7 days after the patient has been bitten by an infected mosquito. There is no specific treatment for chikungunya. Supportive therapy that helps ease symptoms, such as administration of non-steroidal anti-inflammatory drugs, and getting plenty of rest, may be beneficial. Infected persons should be isolated from exposure to mosquitoes for at least 7 days to reduce the risk of transmission of infection to other mosquitoes. Chikungunya disease is believed to be rarely fatal.The main preventive measure is to stop the proliferation of mosquitoes by reducing their breeding grounds as well as avoiding being bitten by mosquitoes through personal protection methods. There is no vaccine although a live attenuated vaccine has been developed by the US military and trialled in the late 1990’s. Further development of the vaccine is still required. The 2006 Reunion Island outbreak may reactivate the research effort to bring the vaccine to licensure.
Travel history should be investigated. Current chikungunya endemic areas include:
- parts of Africa (including Transvaal, Uganda, Congo, Nigeria, Ghana, Zimbabwe, Senegal, Burkina Faso, the Central African Republic, Cameroon, Guinea-Bissau),
- southeast Asia (including Cambodia, Indonesia, Malaysia, Philippines and Timor Leste),
- islands in the Indian Ocean (La Réunion, Madagascar, Mauritius, Cormoros, Seychelles), or
- the Indian-sub-continent (including Pakistan and southern India).
Method of Diagnosis
Clinically the illness is very similar to both RRV disease and BFV disease therefore diagnostic testing should be performed if available. Serological testing for IgG and IgM antibodies is available through the Public Health Laboratory Network member laboratories in each state or territory. It is strongly recommended that acute and convalescent samples are collected whenever possible. Some reference laboratories are able to provide PCR testing for CHIKV in acute samples. However, this is done only in selected cases and is not a substitute for serological testing. The need for CHIKV testing should be clearly indicated on the request form as it is not routinely performed for suspected arbovirus infections in Australia.Laboratory Confirmation
Diagnosis of chikungunya infection is confirmed by:- isolation of CHIKV; or
- detection of CHIKV by nucleic acid testing ; or
- IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to CHIKV, in the absence of a corresponding change in antibody levels to RRV or BFV; or
- detection of CHIKV-specific IgM, in the absence of IgM to RRV or BFV.
Public Health Significance and Occurrence
CHIKV causes a disease that is clinically identical to RRV infection, while severe cases may be mistaken for dengue fever. It is closely related antigenically to RRV and there is some concern that it could be misdiagnosed both clinically and in the laboratory. Although usually a mild disease, arthritis and swollen joints due to CHIKV infection, as found with RRV, can persist for years. In the past, fatal infection has not been described. However, there have been a number of reported fatalities during the current outbreaks. As yet it is not clear whether these are directly related to CHIKV infection.The sizes of recent chikungunya outbreaks from early February 2006 have been substantial. Based on surveillance and mathematical modelling the following have been reported;
- about 255,000 cases on Reunion Island;
- 20,000 cases from Mauritius, Seychelles, Cormoros and Madagascar;
- over100,000 cases from India; and
- 200 cases from Malaysia.
CHIKV is an epidemic-prone disease in many countries of Asia. CHIKV spread through Indonesia during the early 1980’s and was reported to have reached West Papua in 1986. It has again been spreading eastwards through Indonesia since 2002. There is no evidence at present, confirming incursions of CHIKV into Australia although a few visitors and returning residents entering Australia have been diagnosed with the disease.
Reservoir
Humans and monkeys are believed to be the main hosts of CHIKV, but the range of vertebrate hosts is not well understood. The competence of Australian animal species to act as hosts for CHIKV has not been elucidated. More recently, bats have been suggested as hosts of CHIKV raising the question of whether flying foxes and other Australian animal species could be hosts to this virus.Mode of Transmission
Aedes aegypti and Aedes albopictus are major vectors, but others such as Mansonia spp. may also be involved. Aedes aegypti is present in Queensland, although in the past it has also been found in New South Wales, Northern Territory and Western Australia. Aedes albopictus has recently been introduced to the Torres Strait but an elimination program is currently under way. These species have also been reported on Christmas and Cocos Islands. Other Australian Aedes mosquitoes such as Aedes notoscriptus, Aedes vigilax and Aedes camptorhynchus could be vectors and also Culex annulirostris but there are no data at present to support this.Period of Communicability
The duration of viraemia in humans is not known but experiences with other arbovirus infections suggest that it will only be 3-4 days after onset of illness. It is recommended that people with suspected or proven infection avoid mosquito-exposure for at least 7 days after developing symptoms.Chikungunya is a mosquito-borne disease. There is no evidence of direct human-to-human transmission.
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Control Measures
Preventive measures
CHIKV infection can be prevented by:- mosquito control measures;
- personal protection measures (long sleeves and pants, mosquito repellents and mosquito coils); and
- avoidance of mosquito areas, (although most mosquitoes bite between dusk and dawn, Aedes aegypti and Aedes albopictus are day time biters, both indoors and outdoors).
Control of case
Treatment is symptomatic with rest advisable in the acute stages of the disease. Presently, there is no vaccine available commercially to protect against CHIKV disease.Infected persons should be protected from further mosquito exposure (staying indoors and/or under a mosquito net during the first few days of illness) to reduce the risk of local spread of the virus.
Control of contacts
Unreported or undiagnosed cases should be sought in the region where the patient was staying during the incubation period of their illness. All family members should be questioned about symptoms and evaluated serologically if necessary.Control of environment
To reduce/prevent virus transmission, interruption of human/mosquito contact is required by:- suppression of the vector mosquito population; and
- avoidance of vector contact (personal protection/education).
Outbreak Measures
In the event of an outbreak the following should be done:- conduct a survey to determine the species of vector mosquito involved (through virus detection/isolation);
- identify vector breeding places and promote their control;
- promote the use of mosquito repellents and other mosquito avoidance measures for persons exposed to bites because of their occupation, or other reasons; and
- identify the infection among vertebrate animal reservoirs, for example, flying foxes and other bats – if possible.