Effect of passive zooprophylaxis on malaria transmission in The Gambia

The effect of zooprophylaxis on malaria transmission has not been studied on the African continent despite that the World Health Organization has recommended this intervention method since 1982. The effect of passive zooprophylaxis on malaria vector abundance, mosquito feeding preferences, and infectivity was studied in an area of moderate seasonal transmission in The Gambia. A paired cohort of 204 children <7 yr of age was selected and matched in groups for presence or absence of cattle (Bos taurus) within 20 m of their bedroom. Comparisons were made between mosquitoes collected from the bedrooms of the two groups of children. Other ruminants and equines were present in both groups of compounds. Most of the anopheline mosquitoes (98.5%) collected were Anopheles gambiae sensu lato. There was no difference in the geometric mean number of An. gambiae s.l. mosquitoes caught in houses near or far from cattle. The species composition of the An. gambiae complex was similar in both groups. Blood meal analysis of specimens collected in houses without cattle showed a human blood index (HBI) of 82% for An. Arabiensis (Patton), 56% for An. gambiae sensu stricto (Giles), and 36% for Anopheles Melas (Theobald), indicating that each of these sibling species fed readily on animals. The presence of cattle reduced the HBI of An. arabiensis but did not significantly alter the HBI of An. gambiae s.s. or An. melas. There was no significant difference between the groups in the sporozoite rates of An. gambiae s.l. nor in the estimated malaria transmission risk. These findings suggest that passive zooprophylaxis using cattle does not alter the individual exposure to malaria parasites in The Gambia.