CHIKUNGUNYA

The viral disease chikungunya (CHIK) is caused by the chikungunya virus (CHIKV), which is transmitted through the bite of infected day-biting Aedes mosquitoes mainly Aedes aegypti. The term Chikungunya is derived from the Makonde root verb kungunyala, meaning that which bends upon reference to the stooped posture developed due to the excruciating joint and muscle pain and other rheumatologic manifestations.

Geographical distribution: The first outbreak of chikungunya was reported from the Makonde Plateau, along the border between Tanzania and Mozambique, during 1952–1953. After this epidemic the virus has widely disseminated throughout sub-Saharan Africa, India, and countries of Southeast Asia. It is now endemic in several parts of Africa. The first outbreak in Asia was reported from Bangkok in 1958 followed by a number of outbreaks in Cambodia, Vietnam, Malaysia, Taiwan etc. in the subsequent years. The first epidemic of CHIKV in India was reported from Kolkota in 1963, which claimed nearly 200 lives mainly children. Recent outbreak occurred in 2006-07 and continues to be reported from various parts of the country.

Etiology: CHIKV is an alphavirus of the family Togaviridae has a genome consisting of a linear, positive-sense, single stranded RNA molecule of approximately 11.8 kb. Two genotypes exist in Africa namely the West African and East Central South African (ECSA) genotypes. A single genotype represented the entire Asia until 2006 after which ECSA genotype was found in Asia.

Vector: Although Ae. aegypti is the primary vector, Ae. albopictus is also known to play an alternate role. In Asia CHIKV is maintained in a mosquito-human-mosquito cycle while in Africa the virus is maintained in a sylvatic cycle involving wild non-human primates and forest-dwelling Aedes mosquitoes.

Clinical features: The incubation period is usually 2-3 days but may range form 1-12 days. The disease is characterized by sudden onset of fever with arthralgia, which generally resolves within a few days. Patients have high viremia during the first two days of illness, which declines in 3 days and disappears by the fifth day. Cutaneous manifestations include a maculopapular rash commonly involving trunk and limbs. Neurological (meningoencephalitis) and haemorrhagic manifestations (haematemesis and melaena) with a shock-like syndrome leading to death were reported for the first time in 1963 epidemic. The disease is generally non-fatal and the acute phase resolves within 3 to 4 days. The most significant characteristic of CHIK is the prolonged arthralgic syndrome that primarily affects the peripheral small joints associated with excruciating pain. Arthralgia may persist for months and years with excruciating pain in joints and ankles making the people prostrate. The most affected are the aged adults and adults suffering from diabetes, alcoholic hepatopathy and impaired renal functions. The 2007 epidemic also witnessed the first ever mother to child transmission.

Laboratory diagnosis: Serological techniques include haemagglutination inhibition assay, complement fixation and neutralization test. More recently, IgM capture enzyme linked immunosorbent assay (MAC-ELISA) has been used. Virus can be isolated by intracerebral infant mice inoculation, mosquito inoculation, mosquito cell line (C6/36) inoculation and is identified by haemagglutination and neutralization assay. Viral antigens in clinical specimens can be detected and identified by using indirect immunofluorescent antibody technique. Reverse transcription polymerase chain reaction (RT-PCR) is useful in rapid detection of in the rapid diagnosis of CHIKV.

Treatment & prevention: Since no specific drugs are available, supportive treatment for the symptoms i.e. analgesics, antipyretics, anti-inflammatory agents etc is generally administered. Mild exercise may ease stiffness but heavy exercise may exacerbate the condition. Non-aspirin and non-steroidal anti-inflammatory drugs are useful. No vaccines are commercially available and vector control measures are the best measures against this viral infection.