Epidemiology of hepatitis B virus infection among the tribes of Andaman and Nicobar Islands, India.

The Andaman and Nicobar Islands, Union Territory of India, are home to six primitive tribes, namely the Great Andamanese, Onges, Jarawas and Sentinelese (Negrito race), and the Shompens and Nicobarese (Mongoloid race). These tribes account for about 8% of the island's population and the Nicobarese constitute >95% of the tribal population. Hepatitis B virus (HBV) infection is highly endemic among them with the prevalence of hepatitis B surface antigen (HBsAg) ranging from 23% among the Nicobarese to 66% among the Jarawas. The high HBsAg prevalence among pregnant mothers (20.5%), a linear increase in the age-specific rates of HBV exposure and the presence of HBsAg-positive individuals in every family suggested a combination of perinatal and horizontal transmission among the Nicobarese. Molecular studies of HBV isolates from the Onges, Nicobarese and Great Andamanese indicated a predominance of genotype D and there was a close similarity between these isolates and isolates from mainland India, suggesting that HBV may have been introduced from mainland India. In contrast, genotype C predominated among the Jarawas, with isolates similar to strains from Southeast Asian countries. Due to its high prevalence, hepatitis B vaccine is included in the childhood vaccination programme in these islands. It might be worth considering a pilot screening programme for chronic HBV patients to detect hepatocellular carcinoma.