Epidemiology and Infection

Leptospiral infection among primitive tribes of Andaman and Nicobar Islands

S. C. SEHGAL a1c1, P. VIJAYACHARI a1, M. V. MURHEKAR a1, A. P. SUGUNAN a1, S. SHARMA a1 and S. S. SINGH a2
a1 Regional Medical Research Centre (Indian Council of Medical Research), Post Bag No. 13, Port Blair 744 101, Andaman and Nicobar Islands, India
a2 G.B. Pant Hospital, Port Blair


The Andaman islands were known to be endemic for leptospirosis during the early part of the century. Later, for about six decades no information about the status of the disease in these islands was available. In the late 1980s leptospirosis reappeared among the settler population and several outbreaks have been reported with high case fatality rates. Besides settlers, these islands are the home of six primitive tribes of which two are still hostile. These tribes have ample exposure to environment conducive for transmission of leptospirosis. Since no information about the level of endemicity of the disease among the tribes is available, a seroprevalence study was carried out among all the accessible tribes of the islands. A total of 1557 serum samples from four of the tribes were collected and examined for presence of antileptospiral antibodies using Microscopic Agglutination Test (MAT) employing 10 serogroups as antigens. An overall seropositivity rate of 19·1% was observed with the highest rate of 53·5% among the Shompens. The seropositivity rates in the other tribes were 16·4% among Nicobarese, 22·2% among the Onges and 14·8% among the Great Andamanese. All of the tribes except the Onges showed a similar pattern of change in the seroprevalence rates with age. The prevalence rates were rising from low values among children to reach a peak in those aged 21–40 years and then declined. Among Onges the seroprevalence rates continued to rise beyond 40 years. In all the tribes, seroprevalence rates were found to be significantly higher among the males. The commonest serogroups encountered were Australis followed by Grippotyphosa, Icterohaemorrhagiae, Pomona and Canicola.

(Accepted January 15 1998)

c1 Author for correspondence.