Chikungunya fever is a viral illness that is spread by the bites of virus-carrying Aedes mosquitoes. It was first described by Marion Robinson and W.H.R. Lumsden in 1955, following an outbreak in 1952 on the Makonde Plateau, along the border between Mozambique and Tanganyika (the mainland part of modern day Tanzania). “Chikungunya” word comes from the Mankode language meaning “that which bends up”. The word describes the stooped posture developed as a result of the arthritic symptoms of the disease.
Epidemiology
Since its discovery in Tanganyika, Africa in 1952, chikungunya virus outbreaks have occurred occasionally in Africa, South Asia, and Southeast Asia. Between 1960 and 1982, outbreaks of chikungunya fever were reported from Africa and Asia. In Asia, virus strains have been isolated in Bangkok in 1960s; various parts of India including Vellore, Calcutta and Maharastha in 1964; in Sri Lanka in 1969; Vietnam in 1975; Myanmar in 1975 and Indonesia in 1982. After an interval of more than 20 years, chikungunya fever has been reported from several countries including India, Indonesia, Maldives, Thailand and various Indian Ocean islands including Comoros, Mauritius, Reunion and Seychelles. Recent outbreaks have spread the disease over a wider range including limited area in Europe.
Chikungunya virus is an alpha virus closely related to the O’nyong’nyong virus, the Ross River virus in Australia, and the viruses that cause eastern equine encephalitis and western equine encephalitis. Chikungunya is generally spread through bites from Aedes aegypti mosquitoes, but recent research has suggested that chikungunya virus strains in the 2005-2006 Reunion Island outbreaks incurred a mutation that facilitated transmission by Aedes albopictus (Tiger mosquito). Enhanced transmission of chikungunya virus by Aedes albopictus could mean an increased risk for chikungunya outbreaks in other areas where the Asian tiger mosquito is present. A recent epidemic in Italy was likely perpetuated by Aedes albopictus. In Africa, chikungunya is spread via a sylvatic cycle in which the virus largely resides in other primates in between human outbreaks.
Causes
Chikungunya virus is transmitted to humans by the bite of infected mosquitoes, usually of the genus Aedes. Chikungunya virus (CHIKV) is an insect-borne virus. It is a member of the genus Alphavirus, in the family Togaviridae. CHIK fever epidemics are sustained by human-mosquito-human transmission. The main virus reservoirs are monkeys, but other species can also be affected.
Signs and symptoms
The incubation period of Chikungunya disease is from two to four days. Symptoms of the disease include a
· fever up to 40 °C (104 °F) – the fever varies from 2-5 days
· petechial or maculopapular rash of the trunk and occasionally the limbs
· Arthralgia (joint pain) or arthritis affecting multiple joints and affects the joints of the extremities. The pain may lasts for weeks or even months.
· intense headache
· slight photophobia
· insomnia
· extreme degree of prostration
*other non specific symptoms may last for a variable period and maybe longer depending on the age.
Diagnosis
Chikungunya fever is diagnosed based on symptoms, physical findings (e.g., joint swelling), laboratory testing, and the suggestive history (possibility of exposure to infected mosquitoes). Seems that 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.
Common laboratory tests for chikungunya include:
· RT-PCR – Results can be determined in 1-2 days
· virus isolation – provide most definitive diagnosis, but may takes up to 2 weeks for completion
· serological tests – requires a larger amount of blood than the other methods. The results require 2-3 days but false positive result may occur.
Treatment
· There are no specific treatments for Chikungunya. The treatment mainly supportive based on the symptoms for mitigating pain and fever using anti-inflammatory drugs along with rest usually suffices.
· 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.
· There is no vaccine currently available. However, a DNA vaccine for chikungunya virus is currently under research. DNA vaccination is a technique for protecting an organism against disease by injecting it with genetically engineered DNA to produce an immunological response.
· Chloroquine has given promising results as a possible treatment for the symptoms associated with chikungunya, and as an anti-inflammatory agent to combat the arthritis that are not relieved by aspirin and non-steroidal anti-inflammatory drugs (NSAID).
Prevention
There is no vaccine available at the moment, so prevention is one very important aspect how to tackle this problem.
· The most effective means of prevention are protection against contact with the disease-carrying mosquitoes and mosquito control.
· Prevent mosquito bites, for example, wearing bite-proof long sleeves and trousers (pants) also offers protection.
· In addition, garments can be treated with pyrethroids, a class of insecticides that often has repellent properties.
· Securing screens on windows and doors will help to keep mosquitoes out of the house. In the case of the day active Aedes aegypti and Aedes albopictus, however, this will only have a limited effect, since many contacts between the vector and the host occurs outside.
· Reduce mosquito breeding by eliminate the places that allow them to breed (e.g.: variety of rain-filled containers)
Prognosis
Recovery from the disease varies by age and longer time is needed for elderly. Younger patients recover within 5 to 15 days; middle-aged patients may take between 1 to 2 and the half months. The severity of the disease as well as its duration is less in younger patients and pregnant women. In pregnant women, no untoward effects are noticed after the infection.
Ocular inflammation is present in some cases. It may present as iridocyclitis with or without retinal lesions. Pedal edema (swelling of legs) is observed in many patients, the cause of which remains obscure as it is not related to any cardiovascular, renal or hepatic abnormalities.
Conclusion
Chikungunya is not usually fatal but some cases are associated with severe morbidity. Widespread occurrence of diseases may cause economic loss as well. Other than that, chikungunya was one of more than a dozen agents that the United States researched as potential biological weapons before the nation suspended its biological weapons program. That shows that chikungunya is not as simple as it may sound. The dramatic resurgence and geographic extension of chikungunya in recent years underlines our vulnerability to emerging infectious diseases spread by insects and emphasizes the importance of sustained control programmes as an essential component of health security.
Reference:
- http://en.wikipedia.org/wiki/Chikungunya
- http://www.cdc.gov/ncidod/dvbid/chikungunya/
- http://www.who.int/features/qa/63/en/index.html
- http://www.searo.who.int/en/Section10/Section2246.htm
