Well-breeding Anopheles dirus and their role in malaria transmission in Myanmar.

Mosquitos were collected with human and animal baits from March 1996 to January 1998 in four villages located along the Yadana gas pipe line in Yepyu township, Dawae district, Tanintharyi Division, southern Myanmar. A total of 23 anopheline species were collected. Anopheles dirus were abundant in pre-monsoon (May/June) an post-monsoon (October) months. All An. dirus caught both humans and cattle were assayed with specific, sporozoite enzyme-linked immunosorbent assays (ELISAs). A total of 5/250 (2%) caught with human bait was found positive with Plasmodium vivax from Eindayaza, Ohnbinkwin and Thaechaung during rainy and cool-dry months. Larval surveys also showed An. dirus larvae/pupae were caught from domestic wells (6 to 46% found positive). Clinical surveys indicated that transmission is hyperendemic and occur all year round in all four villages.

Hyperendemic malaria in a forested, hilly Myanmar village.

A 1-year longitudinal study of hyperendemic malaria was carried out at Tha-bye-wa village, Oktwin township, situated in the forested Bago mountain range in south-central Myanmar. Mosquito infectivity was assayed using specific, sporozoite enzyme-linked immunosorbent assays. Anopheles dirus was the predominant vector in the postmonsoon season (October); during the cool-dry season (January), both An. dirus and Anopheles minimus were vectors. Members of the Anopheles culicifacies complex were caught in the hot-dry season (April) but none was infective. The entomological inoculation rate was estimated to be at least 13.7 infective bites/person/year. Infective An. dirus were caught feeding on cattle as well as on humans. Three of the 4 positive An. dirus and both positive An. minimus were caught biting humans indoors in the second quarter of the night when most people were sleeping. This suggests that use of insecticide-impregnated bednets in this area could interrupt transmission.