Survey of the relative prevalence of potential yellow fever vectors in north-west Nigeria.

The yellow fever epidemic in Nigeria in 1969-70 emphasized the lack of data concerning the possible importance of Aedes aegypti and other Stegomyia mosquitos as vectors. An entomological survey was therefore undertaken in September 1973 in 6 areas in the north-west of Nigeria to determine the prevalence of Stegomyia populations in the villages. An examination of over 6 700 water pots showed that 11-53% contained A. aegypti larvae, and in some areas larvae of A. vittatus were found in up to 18% of pots. In villages in the relatively dry Sudan savanna neither leaf axils nor tree-holes were important Stegomyia larval habitats, but in the more southern Kontagora area of the wetter northern Guinea savanna, these habitats were probably important breeding sites. In the early evening the most abundant man-biting mosquito in the villages was A. aegypti. A. vittatus was also caught at bait in some villages. It was concluded that the only potential yellow fever vectors in the area were A. aegypti and A. vittatus. There were large populations of A. aegypti, closely associated with man, in all the areas surveyed, but they should not present a risk of yellow fever transmission unless the disease were to be introduced into the area by man, or unless virus reservoirs, such as monkeys, were also present. Although monkeys were common in the Kontagora area they were rare in the Sudan savanna.