Epidemiology of subperiodic Wuchereria bancrofti infection in the Nicobar Islands, India

Diurnally subperiodic filariasis due to Wuchereria bancrofti has been reported from tribal populations in the Nancowry group of islands in the Andaman and Nicobar Islands, India. This was confirmed in a survey carried out during the monsoon season in 1993. Microfilariae were detected in the peripheral blood throughout a 24 h period with a peak at 18:00. The microfilaria (mf) rate ranged from 1.2% to 18.7%, with a low disease rate (mean = 1.9%). Incidence of mf was low in children less than 10 years old (3.5%), but increased with increasing age. Culex (Culex) quinquefasciatus was present at a very low density. Aedes (Finlaya) niveus and Aedes (Stegomyia) malayensis were the only species commonly biting man. The former was incriminated as a vector, and found naturally infected with W. bancrofti (infection and infectivity rates 1.1% and 0.9% respectively). After experimental feeding on donors, W. bancrofti developed to L3 stage larvae in A. niveus but failed to develop in A. malayensis and A. aegypti.