Abstract
Fever of unknown origin broke out in several districts of West Bengal, from August 2007 to December 2007. The cases were suffering from high fever, severe joint pain lasting for several weeks after clinical cure and appearance of skin rashes. Patients’ sera were collected at least five days after fever and were analyzed to detect specific IgM antibodies. A total of 800 patients were investigated and 321 (40.13%) were found to be reactive for Chikungunya antibodies. Of the patients, 66% were male. Predominant signs and symptoms observed in the sero-positive cases were fever (100%), arthralgia (96%) and diffuse erythematous skin rash (94%). Of the patients, 3% had haemorrhagic manifestations. Re-emerging Chikungunya virus spread in epidemic form in several districts of West Bengal after a gap of four decades.
During August 2007 to December 2007, there was a widespread outbreak of an undiagnosed fever in several districts of West Bengal. The patients were thought to be suffering from chikungunya with high fever, severe joint pains lasting for several weeks after a clinical cure and skin rashes. Sera were collected from patients in affected districts, at least 5 days after the onset of the fever; they were analysed by the Department of Virology, Calcutta School of Tropical Medicine using MAC ELISA to detect specific IgM antibodies (supplied by NIV, Pune, India).
The serosurvey was conducted on 800 patients from 18 districts of West Bengal of whom 321 (40.13%), who came from nine of the districts, were reactive. The areas mainly affected were the adjoining districts of southern West Bengal. Interestingly, the districts in northern Bengal appear to have been spared. The percentage of reactive cases varied from 28.94% (Kolkata district) to 66.66% (Howrah district). No reactive specimens were obtained from the districts of Hooghly, Bankura and Uttar Dinajpur (Table 1). The disease affected those aged 6–70 years of age: 43% were aged 31–50 years, 29% were over 50 years of age and 66% were males. Four suspected deaths were encountered (the authenticity of which was not confirmed).
The Seropositivity rate of chikungunya infection in various districts of West Bengal
The clinical manifestations were meticulously recorded in 100 serologically reactive cases which are presented in Table 2.
Predominant signs and symptoms seen in chikungunya seropositive patients
Mosquito species collected from affected areas were Culex quinquefasciatus, C. vishnui, Anophelus acconitus and Armigaris observans. The chikungunya virus was not isolated from the pools of these mosquito species.
This is the maiden authentic record of an invasion of chikungunya in the districts of West Bengal, beyond Kolkata. In the previous year (October 2006), a cluster of fever cases associated with severe arthralgia were reported from the Baduria Block of the North 24 Parganas district of West Bengal. Several such fever cases were investigated, and two out of nine patients’ sera were found to be reactive for specific IgM antibodies (unpublished data, School of Tropical Medicine, 2006). The disease was contained, but reappeared the next year as an epidemic.
It may be recalled that the chikungunya virus was isolated in Kolkata (for the first time in India) 1 during the outbreak of haemorrhagic fever in Kolkata during 1963–1965. An examination of the sera collected in 1960 from Kolkata and elsewhere revealed antibodies to the chikungunya virus indicating that this virus, or an antigenically-related virus, had been active in the area for many years 2 . A serosurvey carried out by School of Tropical Medicine in 1995 in Calcutta (Kolkata) and its suburbs 3 revealed the presence of chikungunya antibodies in only 4.37% of the population and only to those above the age of 50. The disease had been quiescent for almost three decades.
The present outbreak is of considerable importance, as it had involved not only the city of Kolkata but also other areas of rural West Bengal. Why and how this resurgence took place after a break of about 43 years should be investigated. Chikungunya also occurred in several states of India in epidemic form during 2006–2007. It is important to discover the vector(s) in order to formulate control strategies. It is important that genetic studies of viruses should also be undertaken investigated in the light of the emergence of mutation(s).