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Chikungunya Fever


Chikungunya fever, a viral disease transmitted by the bite of infected mosquitoes(Aedes aegypti (the yellow fever mosquito)) to humans. Chikungunya virus (CHIKV) is a member of the genus Alphavirus, in the family Togaviridae. CHIKV was first isolated from the blood of a febrile patient in Tanzania in 1953, and has since been identified repeatedly in west, central and southern Africa and many areas of Asia, and has been cited as the cause of numerous human epidemics in those areas since that time. The virus circulates throughout much of Africa and Asia, with transmission thought to occur mainly between mosquitoes and monkeys.


Illness Causes by chikungunya virus

CHIKV infection can cause a debilitating illness, most often characterized by fever, headache, fatigue, nausea, vomiting, muscle pain, rash, and joint pain.

The incubation period (time from infection to illness) can be 2-12 days, but is usually 3-7 days. "Silent" CHIKV infections (infections without illness) do occur; but how commonly this happens is not yet known.

After an this incubation period a sudden onset of flu-like symptoms including a severe headache, chills, fever (>40°C,104°F), joint pain, nausea and vomiting. The joints of the extermities in particular become swollen and painful to the touch. A rash may sometimes occur. Hemorrhage is rare and all but a few patients recover within 3-5 days. Some can suffer for joint pain for months. Children may display neurological symptoms.

Acute chikungunya fever typically lasts a few days to a couple of weeks, but as with dengue, West Nile fever, o'nyong-nyong fever and other arboviral fevers, some patients have prolonged fatigue lasting several weeks. Additionally, some patients have reported incapacitating joint pain, or arthritis which may last for weeks or months. The prolonged joint pain associated with CHIKV is not typical of dengue. Co-circulation of dengue fever in many areas may mean that chikungunya fever cases are sometimes clinically misdiagnosed as dengue infections, therefore the incidence of chikungunya fever could be much higher than what has been previously reported.


How one can be infected with chikungunya virus?

CHIKV is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on a person infected with CHIKV. Monkeys, and possibly other wild animals, may also serve as reservoirs of the virus. Infected mosquitoes can then spread the virus to other humans when they bite.


Aedes aegypti (the yellow fever mosquito), a household container breeder and aggressive daytime biter which is attracted to humans, is the primary vector of CHIKV to humans. Aedes albopictus (the Asian tiger mosquito) may also play a role in human transmission is Asia, and various forest-dwelling mosquito species in Africa have been found to be infected with the virus.


Known Treatments

No vaccine or specific antiviral treatment for chikungunya fever is available. Treatment is symptomatic--rest, fluids, and ibuprofen, naproxen, acetaminophen, or paracetamol may relieve symptoms of fever and aching. Aspirin should be avoided during the acute stages of the illness.

While recovery from chikungunya is the expected outcome, convalescence can be prolonged (up to a year or more), and persistent joint pain may require analgesic (pain medication) and long-term anti-inflammatory therapy

Infected persons should be protected from further mosquito exposure (staying indoors and/or under a mosquito net during the first few days of illness) so that they can't contribute to the transmission cycle.


How to Prevent

The best way to avoid CHIKV infection is to prevent mosquito bites. There is no vaccine or preventive drug.


Prevention tips

  • Wear long sleeves and pants (ideally treat clothes with permethrin or another repellent).
  • Have secure screens on windows and doors to keep mosquitoes out.
  • Get rid of mosquito breeding sites by emptying standing water from flower pots, buckets and barrels.
  • Change the water in pet dishes and replace the water in bird baths weekly.
  • Drill holes in tire swings so water drains out. Keep children's wading pools empty and on their sides when they aren't being used.
  • Additionally, a person with chikungunya fever or dengue should limit their exposure to mosquito bites in order to avoid further spreading the infection and the person should stay indoors or under a mosquito net.


To prevent mosquito breeding

The Aedes mosquitoes that transmit chikungunya breed in a wide variety of manmade containers which are common around human dwellings. These containers collect rainwater, and include discarded tires, flowerpots, old oil drums, animal water troughs, water storage vessels, and plastic food containers. These breeding sites can be eliminated by
  • Draining water from coolers, tanks, barrels, drums and buckets, etc..
  • Emptying coolers when not in use
  • Removing from the house all objects, e.g. plant saucers, etc. which have water collected in them
  • Cooperating with the public health authorities in anti-mosquito measures.



Laboratory Diagnosis of Chikungunya Fevers



The clinical manifestations of chikungunya fever resemble those of dengue fever. Laboratory diagnosis is critical to establish the cause of diagnosis and initiate specific public health response


Types of Laboratory tests available and specimens required

Three main laboratory tests are used for diagnosing Chikungunya fevers: virus isolation, serological tests and molecular technique of Polymerase Chain Reaction (PCR).


Virus isolation

Virus isolation is the most definitive tests. Between 2-5 ml of whole blood is collected during the first week of illness in commercial heparinzed tube and transported on ice to the laboratory. The CHIK virus produces cytopathic effects in a variety of cell lines including BHK-21, HeLa and Vero cells. The cytopathic effects must be confirmed by CHIK specific antiserum and the results can take between 1-2 weeks. Virus isolation must only be carried in BSL-3 laboratories to reduce the risk of viral transmission.


RT-PCR

Recently, a reverse transcriptase, RT- PCR technique for diagnosing CHIK virus has been developed using nested primer pairs amplifying specific components of three structural gene regions, Capsid (C ), Envelope E-2 and part of Envelope E1. PCR results can be available from within 1-2 days. Specimens for PCR is same as the virus isolation i.e. heparized whole blood


Serological diagnosis

For serological diagnosis between 10-15 ml of whole blood sera are required; an acute phase serum must be collected immediately after clinical onset and a convalescent phase serum10-14 after the disease onset. The blood specimen is transported at 4 degrees and not frozen to the laboratory immediately. If testing cannot be done immediately, the blood specimen is separated into sera that should be stored and shipped frozen.

Serologic diagnosis can be made by demonstration of fourfold increase in antibody in acute and convalescent sera or demonstrating IgM antibodies specific for CHIK virus. A commonly used test is the Immunoglobulin M Antibody (IgM) capture enzyme-linked immunosorbent assay (MAC-ELISA). Results of MAC-ELISA can be available within 2-3 days. Cross-reaction with other flavirus antibodies such as o’nyong-nyong and Semliki Forest occur in the MAC-ELISA; however, the latter viruses are relatively rare in South East Asia but if further confirmation is required it can be done by neutralization tests and Hemagglutination Inhibition Assay (HIA).


Interpretation of results

Sero-diagnosis rests on demonstrating a fourfold increase in CHIK IgG titer between the acute and convalescent phase sera. However, getting paired sera is usually not practical. Alternatively, the demonstration of IgM antibodies specific for Chikungunya virus in acute-phase sera is used in instances where paired sera cannot be collected.

A positive virus culture supplemented with neutralization is taken as definitive proof for the presence of Chikungunya virus.

PCR results for E1 and C genome either singly or together constitute a positive result for Chikungunya virus.


Existing Laboratory Network for Diagnosing Chikungunya in South Asia

Country Serological Test PCR test
India National Institute of Virology, Pune National Institute of Virology, Pune
Indonesia NIHRD, NAMRU-2 NIHRD ,NAMRU-2
Myanmar Department of Medical Research NA
Sri Lanka Medical Research Institute Medical Research Institute
Thailand NIH, Bangkok, AFRIMS NIH, Bangkok, AFRIMS


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