The Malarial Infectivity of an African Village Population to Mosquitoes (Anopheles Gambiae)

Abstract

Summary The malarial infectivity of an African village community with particular reference to Plasmodium falciparum has been tested by selecting subjects at random, irrespective of their blood picture, and feeding batches of laboratory-bred Anopheles gambiae on them. The degree of infectiousness has been judged by the number and identity of oöcysts found in the stomach of the engorged mosquitoes after varying periods of incubation. Random tests on 347 subjects of all ages indicate that for every 100 individuals in the African village population of average age composition there are at any one time about 10 or 11 individuals capable of infecting mosquitoes with malaria parasites, mainly P. falciparum. All age groups contribute to this infective reservoir, the actual numbers observed being 4.2 infants and toddlers (under 5 years), 3.0 school children (5 to 14 years) and 3.3 adolescents and adults (15 years and over). Most of the infections picked up in this random survey had a low infectivity to mosquitoes. There is no indication that unusually high infectivity is necessarily associated with the lower age groups. It is considered that under these conditions of “hyperendemic” malaria, adolescents and adults form at least 30 per cent of the total reservoir of malaria infection in the human population.