Prevalence of larvae of potential yellow fever vectors in domestic water containers in south-east Nigeria.

The seasonal variation in prevalence of Aedes (Stegomyia) mosquitos breeding in peridomestic water containers was assessed in an urban quarter of Enugu, Nigeria, and in two rural villages located among forest relicts in the neighbouring Udi Hills. A large number of earthenware pots, most of which contained water in the wet season, were present in the compounds around houses. Monthly determinations of the presence or absence of Aedes larvae in these containers were made for 13 consecutive months. The average Breteau index (positive containers per 100 houses) for A. aegypti during the 7-month wet season was 53 in one of the villages and 76 in the other, suggesting a high risk of yellow fever transmission; the dry-season averages were 11 and 23. In the urban quarter the wet-season average was 29; the dry-season average was 4.7, a level at which transmission is unlikely to occur. A. luteocephalus were occasionally found in containers in both the urban and rural localities, and A. africanus larvae occurred in one of the villages. Although Culex larvae were common, mixed infestations of Aedes and Culex were so uncommon that the simplified "single larva" method of sampling for Aedes gave similar results to the conventional method. The multiplicity of peridomestic containers in this part of Nigeria made the container index inadequate as a measure of larval density.