Historically, CHIKV has been endemic in tropical and subtropical regions of sub-Saharan Africa and Southeast Asia, where two distinct CHIKV transmission cycles exist. CHIKV is maintained in a rural enzootic transmission cycle, which occurs between various forest or savannah Aedes (Stegomyia) mosquitoes and animal reservoirs, with nonhuman primates being the presumed major reservoir host
Chikungunya virus (CHIKV):CHIKV is a small (~70 nm in diameter), enveloped virus that is a member of the Old World Semliki Forest virus group of arthritogenic alphaviruses within the Togaviridae family
Transmission:Transmission of CHIKV occurs mainly through the bite of an infected Aedes (subgenus Stegomyia) species of mosquito. However, maternal-fetal transmission can occur intrapartum, which results in high rates of infant morbidity
- Enzootic sylvan transmission (animal-mosquito-human): Well established in Africa
- Mediated by: Aedes africans, A. fancifer and wild primates
- Urban cycle (human-mosquito-human transmission cycle): Found in Asia on occasional introduction into urban areas causing periodic outbreaks of CHIKV disease
- Mediated by: Aedes aegypti or albopictus mosquitoes
CHIKV-induced disease shares many similarities with illnesses caused by other arthritogenic alphaviruses, with some distinctions observed. After deposition into the bloodstream or skin through a bite of an infected mosquito, CHIKV replicates at the site of inoculation in fibroblasts and possibly macrophages. Despite triggering innate immune responses, the virus spreads via lymphatics into the bloodstream, allowing dissemination to several sites of replication, most commonly lymphoid organs (lymph nodes and spleen), skin, and especially tissues where prominent disease symptoms occur (muscle, peripheral joints, and tendons) but also in brain and liver in more severe cases. Replication of CHIKV in peripheral tissues results in remarkably high serum viral loads (>109 virus particles/ml; ref. 110). Such high-level viremia in humans is rare for most alphaviruses and allows CHIKV to be easily transmitted to mosquitoes via a bloodmeal.
- Incubation period: 2-12 days
- Sudden onset of symptoms
Characteristic triad:The vast majority of infected individuals develop chikungunya fever, an acute illness notable for rapid onset of fever, incapacitating polyarthralgia and arthritis, rash, myalgia, and headache
- Fever: Rises abruptly to 103-104°F and is accompanied by rigors
- Rash (4-8 days later): Itchy, transient maculopapular rash affecting the trunk and limbs
- Arthritis: Polyarticular arthralgia/arthritis, migratory and predominantly affects the small joints of hands, wrist, ankle and feet, with less involvement of larger joints. Appears suddenly and is often very severe in intensity and may continue for many months after illness
- Headache (80% cases)
- Fatigue, nausea, vomiting, muscle pain
- Photophobia and retro-orbital pain
Complications (rare):CHIKV disease is often self-limiting and has a low fatality rate (~0.1%), but manifestations of CHIKV infection that lead to acute and chronic disability have considerable implications, including a substantial impact on quality of life for infected patients as well as considerable economic and community consequences
- Thrombocytopenia and shock
Diagnosis of CHIKV can be established or confirmed by detection of viral RNA with serology and/or reverse-transcription polymerase chain reaction (RT-PCR) depending on disease timeframe presentation.
Viral culture:The gold standard for the diagnosis of Chikungunya fever is viral culture based on inoculation of mosquito cell cultures, mosquitoes, mammalian cell cultures, or mice. However, viral culture is seldom done in routine clinical practice as these facilities are not widely available in India. It has the advantage of detecting a wide range of viruses.
- Real-time loop-mediated isothermal amplification (RT-LAMP)
Serodiagnosis:Serodiagnostic methods for the detection of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies against Chikungunya virus in acute and convalescent sera are used. IgM antibodies are detectable after a mean period of 2 days by ELISA immunofluorescent assay and they persist for periods ranging from several weeks to 3 months.. The IgG antibodies can be detected in convalescent samples and persists for years. Instances of persistence of IgM antibodies 18 months after disease onset in about 40% of symptomatic patients has also been described.
- Enzyme-linked immunosorbent assay (ELISA)
- Indirect immunofluorescent method
- Hemagglutination inhibition
- Neutralization techniques
- Dengue fever: Acute CHIKV disease symptomatically resembles dengue fever. However, unlike dengue, a characteristic feature of CHIKV disease is recurring musculoskeletal disease primarily affecting the peripheral joints that can persist for months to years after acute infection
Symptomatic treatment:Treatment of Chikungunya fever is symptomatic and supportive.
- Rest, adequate fluid intake
- Paracetamol or nonsteroidal anti-inflammatory drugs (NSAIDS): Symptom relief
Aspirin: Avoided due to effect on platelets
Subacute & chronic disease:Chronic manifestations, including persistent or relapsing-remitting polyarthralgia, polyarthritis, and myalgia, have been found to respond adequately to hydroxychloroquine in combination with corticosteroids or other disease modifying anti-rheumatic drugs (DMARDs)
Patients with Chikungunya fever should be advised to avoid being bitten by mosquitoes as the disease can be transmitted to others. Presently no commercial vaccine is available for Chikungunya fever in India, although some candidate vaccines are being tested in human beings.
Vector surveillance and control:Educating the community and public health officials, vector control measures such as elimination of breeding sites and spraying of insecticides should be initiated at the individual and community levels as this can be rewarding. Vector surveillance and control is a key element in containing Chikungunya fever epidemics. Active involvement of community and public health authorities with regard to hygiene and mosquito control measures is essential to stand a chance in the war against the mosquitoes.
- Integrated vector management: Reduce or interrupt transmission of disease