Chikungunya is a viral disease transmitted by Aedes mosquitoes to vertebrates. The word ‘chikungunya’ means 'which bends up', an allusion to the posture of the suffering patients. The most common clinical form associates fever, rash and arthralgia. Recovery is the usual output but chronic arthritis is not rare. Diagnostic tests are available but there is no antiviral or licensed vaccine. The disease is notifiable at EU level.
In 2005-2006, an African genotype has been introduced into Asia. Outbreaks occurred in Kenya, Comoros, La Reunion, Madagascar, India. Imported cases were found in Asia, Australia, USA, Canada and continental Europe (Italy, Spain, Corsica, France, UK, Switzerland, Belgium, Czech Republic, Germany, Norway). In 2009, outbreaks took place in Italy and Southeast-Asia and, in 2010, autochthonous cases were reported in France. The risk of Chikungunya spreading in EU is high due to travel importation, presence of competent vectors in many countries (particularly around the Mediterranean coast, from Spain to Greece) and population susceptibility.
- The virus was first identified in Tanzania in 1953.
- The virus is a single-stranded positive-sense RNA enveloped virus from the Togaviridae family, genus Alphavirus. The virus is a member of the Semliki Forest Virus serogroup that includes Ross River virus (Australia and Pacific) and O’nyong-nyong virus (Africa).
- There are three different viral genotypes of chikungunya virus. They were reflecting the geographical distribution (West Africa, East-Central-South Africa and Asia) until the spread of the East African serotype to Asia in 2006.
- Chikungunya virus is endemic to Africa, Southeast Asia and the Indian subcontinent. The virus has been identified in sub-Saharan Africa, India, Sri Lanka, South East Asia and more recently in the Indian Ocean islands. The virus has subsequently been isolated in Europe and the United States, where it is thought to have been imported by infected travellers returning from areas with high incidence rates. But, in 2007, the virus caused the first outbreak in continental Europe (north-east of Italy) and autochthonous transmission of the virus was detected in France in 2010.
- Humans are the major source, or reservoir, of chikungunya virus. However, in Africa natural hosts of chikungunya virus are wild primates bitten by forest-dwelling Aedes mosquitoes and the sylvatic cycle also involves other small mammals such as bats. There is no evidence of a similar cycle of transmission in Asia but the virus has recently been isolated from monkeys in Malaysia.
- One amino-acid change (A226V) in the E1 glycoprotein of CHIKV has been associated with a gain of fitness adaptation for dissemination by Ae. albopictus mosquitoes. Further mutations in E1 and E2 glycoproteins also modify mosquito infectivity.
Clinical features and sequelae
- Asymptomatic infections are reported in 10–15% of the cases.
- The disease is characterised by a sudden onset of fever, chills, headache, nausea, photophobia, vomiting, incapacitating joint pain and petechial or maculopapular rash.
- The acute phase lasts for about 10 days. The typical clinical sign of the diseases is arthralgia but neurological, haemorrhagic and ocular manifestations have also been described.
- In the chronic phase of the disease, recurrent joint pain is experienced by 30–40% of those infected. It can last for years in some cases.
- In the elderly, arthralgia can evolve to a chronic rhumatoid arthritis syndrome. Meningoencephalitis is also an important sequel, it affects primarily neonates.
- Despite being considered as a non-fatal disease, deaths have been partly attributed to the virus. During the 2005-2006 outbreak in La Réunion the overall mortality rate associated with chikungunya virus infection was 0.3/1,000 persons and mortality rate increased markedly with age.
- The incubation period ranges from 1 to 12 days, with an average of 3–7 days.
- In humans, the viral load in the blood can be very high at the beginning of the illness and lasts 5–6 days (up to 10 days), allowing mosquitoes to feed and disseminate the virus.
- Chikungunya is spread by the bite of Aedes mosquitoes, primarily Aedes aegypti and Aedes albopictus, which are active during the day. Once a person has recovered from chikungunya infection, they can be considered as immunized against subsequent infections.
- The distribution of Ae. albopictus has expanded recently. Native to Southeast Asia, it has colonized both tropical and temperate regions. Currently, it is present in at least 12 European countries (primarily along the Mediterranean coast) and in around 25% of the United States.
- Mother-to-child transmission has also been reported in women who developed the disease within the final week prior to delivery. There are rare reports of spontaneous abortions following maternal chikungunya virus infection. There is no evidence that the virus is transmitted through breast milk.
- Chikungunya virus can be identified using RT-PCR or viral isolation during the first week of illness. Serological diagnosis can be performed by detection of specific IgM antibodies in serum specimen from day 4–5 after the onset of illness, or a four-fold rise of specific CHIK IgG antibody titre on a pair of sera (acute and convalescent specimens). Specific IgM can persist for many months, in particular in patients with long-lasting arthralgia.
- Serological cross-reactions between closely related alphaviruses have been reported.
Case Management and treatment
- Due to the absence of specific antiviral drugs, the treatment is symptomatic including non-salicylate analgesics and non-steroid anti-inflammatory therapy.
- During the past 50 years, numerous re-emergences of chikungunya have been documented in both Africa and Asia, with irregular intervals of 2–20 years between outbreaks.
- In 2004, chikungunya emerged in Kenya. The disease spread to Comoros, other islands in the Indian Ocean and India.
- In La Reunion, an estimated 244,000 cases of chikungunya virus infections and 203 resultant deaths were reported between April 2005 and April 2006.
- On the European continent, the first autochthonous outbreak occurred in Italy in 2007 (217 laboratory-confirmed cases). This was the first outbreak reported in a non-tropical region where a competent vector for the chikungunya virus was present. In 2010, two autochthonous cases linked to imported cases were detected in France.
- Currently, chikungunya fever has been identified in more than 40 countries.
- After the chikungunya outbreaks in the Indian Ocean in 2005–2006 and in Italy in 2007, the European Centre for Disease prevention and Control (ECDC) evaluated the risk for human health in Europe related to chikungunya virus, through several expert consultations. Areas at risk for chikungunya outbreaks, based on the current (and assumed future) distribution of Aedes albopictus in Europe, were identified. A network for arthropod vector surveillance for human public health was established in order to improve the surveillance of competent vectors for infectious diseases, including chikungunya. Regarding the overseas countries and territories, particular needs to respond to communicable disease outbreaks, including chikungunya, have been assessed.
Public health control measures
- It is important to reduce the number of mosquito breeding sites in outdoor/indoor areas by draining or discarding sources of standing water (e.g. flower plates and pots, used tyres, tree-holes and rock pools) and tightly covering water containers, barrels, wells and water storage tanks.
- Measures aiming to control adult mosquito vectors can be applied in an outbreak situation.
- No vaccine or prophylactic drug is available yet. A few research projects have been undertaken on vaccine.
Personal protection and prevention
- All persons who are not immune to chikungunya may become infected with the virus. Exposure to infected mosquitoes represents the principal risk for infection.
- The last weeks of pregnancy, very young (neonatal) and older age are noted as a risk factor for more severe disease and co-morbidities (underlying diseases) as risk factor for poor disease outcome.
- Prevention of chikungunya is currently based on protection against mosquito bites.
- Individual protective measures to avoid mosquito bites during the day should include:
- application of insect repellents on exposed skin: the type and concentration of repellents depend on age and presence of pregnancy;
- wearing appropriate clothing (long sleeves and trousers);
- use of a mosquito net (preferably insecticide-treated), particularly recommended for children and viraemic patients.
- Infected persons should avoid mosquito bites during the first few days of illness to prevent further dissemination of the virus.
Advice to travellers
- As of September 2011, Chikungunya fever transmission has been reported in Sub-Saharan Africa (from Senegal to Somalia and up to South Africa), in the Indian Ocean and Asia (from India and Pakistan to the Philippines and Papua New Guinea), in the Pacific region (New Caledonia) and in Europe (Italy, France).
- Given the chikungunya epidemics and the worldwide distribution of the vectors Ae. aegypti and Ae. albopictus, the risk of importation of the virus into new areas by infected travellers needs to be considered.
- According to the broad distribution of the disease, imported cases can be observed all along the year but locally the transmission usually occurs during or just after the hot rainy season even though it may also occur during another period of the year.
- The risks during pregnancy should be taken into account if travelling in a country experiencing an outbreak.
- The person who believes to be infected should consult a doctor and inform him/her about recent travel history.
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