From the
WORLD HEALTH ORGANIZATION - WHO
Key Facts
- Chikungunya is a viral disease transmitted to humans by infected
mosquitoes. It causes fever and severe joint pain. Other symptoms
include muscle pain, headache, nausea, fatigue and rash.
- The disease shares some clinical signs with dengue, and can be misdiagnosed in areas where dengue is common.
- There is no cure for the disease. Treatment is focused on relieving the symptoms.
- The proximity of mosquito breeding sites to human habitation is a significant risk factor for chikungunya.
- Since 2004, chikungunya fever has reached epidemic proportions, with considerable morbidity and suffering.
- The disease occurs in Africa, Asia and the Indian subcontinent.
In recent decades mosquito vectors of chikungunya have spread to Europe
and the Americas. In 2007, disease transmission was reported for the
first time in a localized outbreak in north-eastern Italy.
Chikungunya is a mosquito-borne viral disease first described
during an outbreak in southern Tanzania in 1952. It is an RNA virus that
belongs to the alphavirus genus of the family Togaviridae. The name
‘chikungunya’ derives from a word in the Kimakonde language, meaning "to
become contorted" and describes the stooped appearance of sufferers
with joint pain (arthralgia).
Signs and symptoms
Chikungunya is characterized by an abrupt onset of fever
frequently accompanied by joint pain. Other common signs and symptoms
include muscle pain, headache, nausea, fatigue and rash. The joint pain
is often very debilitating, but usually lasts for a few days or may be
prolonged to weeks.
Most patients recover fully, but in some cases joint pain may
persist for several months, or even years. Occasional cases of eye,
neurological and heart complications have been reported, as well as
gastrointestinal complaints. Serious complications are not common, but
in older people, the disease can contribute to the cause of death. Often
symptoms in infected individuals are mild and the infection may go
unrecognized, or be misdiagnosed in areas where dengue occurs.
Transmission
Chikungunya has been identified in nearly 40 countries in Asia, Africa, Europe and also in the Americas.
![Chikungunya map]()
WHO
The virus is transmitted from human to human by the bites of
infected female mosquitoes. Most commonly, the mosquitoes involved are Aedes aegypti and Aedes albopictus,
two species which can also transmit other mosquito-borne viruses,
including dengue. These mosquitoes can be found biting throughout
daylight hours, though there may be peaks of activity in the early
morning and late afternoon. Both species are found biting outdoors, but Ae. aegypti will also readily feed indoors.
After the bite of an infected mosquito, onset of illness
occurs usually between four and eight days but can range from two to 12
days.
Diagnosis
Several methods can be used for diagnosis. Serological tests,
such as enzyme-linked immunosorbent assays (ELISA), may confirm the
presence of IgM and IgG anti-chikungunya antibodies. IgM antibody levels
are highest three to five weeks after the onset of illness and persist
for about two months. Samples collected during the first week after the
onset of symptoms should be tested by both serological and virological
methods (RT-PCR).
The virus may be isolated from the blood during the first few
days of infection. Various reverse transcriptase–polymerase chain
reaction (RT–PCR) methods are available but are of variable sensitivity.
Some are suited to clinical diagnosis. RT–PCR products from clinical
samples may also be used for genotyping of the virus, allowing
comparisons with virus samples from various geographical sources.
Treatment
There is no specific antiviral drug treatment for Chikungunya.
Treatment is directed primarily at relieving the symptoms, including
the joint pain using anti-pyretics, optimal analgesics and fluids. There
is no commercial chikungunya vaccine.
Prevention and control
The proximity of mosquito vector breeding sites to human
habitation is a significant risk factor for chikungunya as well as for
other diseases that these species transmit. Prevention and control
relies heavily on reducing the number of natural and artificial
water-filled container habitats that support breeding of the mosquitoes.
This requires mobilization of affected communities. During outbreaks,
insecticides may be sprayed to kill flying mosquitoes, applied to
surfaces in and around containers where the mosquitoes land, and used to
treat water in containers to kill the immature larvae.
For protection during outbreaks of chikungunya, clothing which
minimizes skin exposure to the day-biting vectors is advised.
Repellents can be applied to exposed skin or to clothing in strict
accordance with product label instructions. Repellents should contain
DEET (N, N-diethyl-3-methylbenzamide), IR3535
(3-[N-acetyl-N-butyl]-aminopropionic acid ethyl ester) or icaridin
(1-piperidinecarboxylic acid, 2-(2-hydroxyethyl)-1-methylpropylester).
For those who sleep during the daytime, particularly young children, or
sick or older people, insecticide treated mosquito nets afford good
protection. Mosquito coils or other insecticide vaporizers may also
reduce indoor biting.
Basic precautions should be taken by people traveling to risk
areas and these include use of repellents, wearing long sleeves and
pants and ensuring rooms are fitted with screens to prevent mosquitoes
from entering.
Disease outbreaks
Chikungunya occurs in Africa, Asia and the Indian
subcontinent. Human infections in Africa have been at relatively low
levels for a number of years, but in 1999-2000 there was a large
outbreak in the Democratic Republic of the Congo, and in 2007 there was
an outbreak in Gabon.
Starting in February 2005, a major outbreak of chikungunya
occurred in islands of the Indian Ocean. A large number of imported
cases in Europe were associated with this outbreak, mostly in 2006 when
the Indian Ocean epidemic was at its peak. A large outbreak of
chikungunya in India occurred in 2006 and 2007. Several other countries
in South-East Asia were also affected. Since 2005, India, Indonesia,
Thailand, Maldives and Myanmar have reported over 1.9 million cases. In
2007 transmission was reported for the first time in Europe, in a
localized outbreak in north-eastern Italy. There were 197 cases recorded
during this outbreak and it confirmed that mosquito-borne outbreaks by
Ae. Albopictus are plausible in Europe.
In December 2013, France reported 2 laboratory-confirmed
autochthonous (native) cases of chikungunya in the French part of the
Caribbean island of St Martin. Since then, local transmission has been
confirmed in the Dutch part of Saint Martin [St Maarten], Anguilla,
British Virgin Islands, Dominica, French Guiana, Guadeloupe, Martinique
and St Barthelemy. Aruba only reported imported cases.
This is the first documented outbreak of chikungunya with autochthonous transmission in the Americas.
As of 6 March 2014, there have been over 8000 suspected cases in the region.
More about disease vectors
Both Ae. aegypti and Ae. albopictus have been implicated in large outbreaks of chikungunya. Whereas Ae. aegypti is confined within the tropics and sub-tropics, Ae. albopictus also occurs in temperate and even cold temperate regions. In recent decades Ae. albopictus has spread from Asia to become established in areas of Africa, Europe and the Americas.
The species Ae. albopictus thrives in a wider range of water-filled breeding sites than Ae. aegypti,
including coconut husks, cocoa pods, bamboo stumps, tree holes and rock
pools, in addition to artificial containers such as vehicle tyres and
saucers beneath plant pots. This diversity of habitats explains the
abundance of Ae. albopictus in rural as well as peri-urban areas and shady city parks.
Ae. aegypti is more closely associated with human
habitation and uses indoor breeding sites, including flower vases, water
storage vessels and concrete water tanks in bathrooms, as well as the
same artificial outdoor habitats as Ae. albopictus.
In Africa several other mosquito vectors have been implicated in disease transmission, including species of the A. furcifer-taylori group and A. luteocephalus. There is evidence that some animals, including non-primates, rodents, birds and small mammals may act as reservoirs.
WHO response
WHO responds to chikungunya by:
- formulating evidence-based 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 for case management, vector control for Member States.
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