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

Abstract

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.

Bancroftian Filariasis in Tribal Population of Bankura District, West Bengal, India.

“…1 to 16 in one season (one season includes 4 months i. e. 16 wks) . Collections were made in all the seasons of the year namely rainy (JulOct) , winter (Nov-Feb) and summer (Mar-Jun) following the method of De and Chandra (1994 Mf rate among the tribal population of the present study area (3.3%) was almost same to that of the tribes of Panna district (3.8%) , Madhya Pradesh (Chand et al, 1996) and much lower than that of the tribes of Nancowry group of islands (11.9%) in Andaman and Nicobar islands (Tewari et al, 1995) . Information on filarial endericity among the tribes of India is very limited.…”

Diurnally subperiodic filariasis in India—prospects of elimination: precept to action?

“…The first report on the prevalence of DspWB, transmitted by O. niveus (now known as Downsiomyia nivea; Reinert et al 2004), came from Nicobar group of islands in 1974 (Kalra 1974). Subsequent studies on its prevalence, distribution, and assessment of endemicity status (Russel et al 1975;Tewari et al 1995;Shriram et al 2002), vector incrimination (Tewari et al 1995), clinical epidemiology (Shriram et al 2002), hostfeeding activity (Shriram et al 2005), transmission dynamics (Shriram et al 2008), and vector population dynamics and bioecology (Shriram and Krishnamoorthy 2010) of this infection have shown its prevalence in all the seven islands of Nancowry group of islands of the Nicobar district and confirmed its continued existence with perennial transmission.…”

Genetic variability of diurnally sub-periodic Wuchereria bancrofti in Nicobarese tribe of Nicobar group of Islands, Andaman and Nicobar Islands, India

“…In case of parasites that are transmitted by vectors, the number of vectors, their density and diversity, flight ranges, vectorial competence, and capacity contribute significantly to the parasite diversity. The only vector of the sub-periodic W. bancrofti in Nicobar group of islands is Ochlerotatus (Finlaya) niveus (Tewari et al 1995), whereas in Car Nicobar island alone, Culex quinquefasciatus is the vector (Table 1). Hence, the evolution of this parasite strain appears to be gearing towards the biting cycle of the vector, C. quinquefasciatus, which is unique to this island unlike the vector in other islands, O. niveus, whose biting activity was observed throughout the day with peak biting habit at dawn and dusk exhibiting bimodal peak.…”

“…Basu (1958) reported for the first time filarial infection in blood samples (9%) collected in the daytime from Nicobar Islands. Subsequently, Kalra (1974), Russel et al (1975), and Tewari et al (1995) have recorded diurnally subperiodic filariasis among nicobarese of Nancowry group of islands. The parasite populations in these islands are separated geographically due to sea barriers, which might have led to reproductive isolation and consequently the divergence of the species (Piessens et al 1987).…”