Arbovirus studies in nupeko forest, a possible natural focus of yellow fever virus in Nigeria II. Entomological investigations and viruses isolated

Abstract

Mosquitoes were collected by several methods during different times of the year in Nupeko Forest; this area is thought to be enzoodemic for yellow fever virus. Potential vectors in the subgenus Stegomyia included Aedes africanus, Ae. luteocephalus, Ae. aegypti, and Ae. simpsoni. Stegomyia populations were very low. Ae. luteocephalus was nevertheless captured on human bait during both the wet and dry seasons, and may be important in maintenance of yellow fever virus transmission. The predominant mosquito in Nupeko Forest was Mansonia africana; this species was captured year-round by various methods including human bait and monkey-baited traps set at various elevations in the forest. No isolates of yellow fever virus were made from the mosquito collections. It is suggested that continuous circulation of yellow fever virus in foci such as Nupeko Forest, which have limited populations of susceptible vertebrate hosts, may depend upon a transmission cycle involving a biologically inefficient vector (e.g. M. africana) or an efficient vector present in small numbers (e.g. Ae. luteocephalus).