Origin of blood meals in indoor and outdoor resting malaria vectors in western Kenya.

Blood meals were obtained from indoor and outdoor resting malaria vectors in three villages of western Kenya and tested by sandwich ELISA to determine host preferences and their human blood index (HBI). Anopheles gambiae s.s. collected indoors at Kisian village had a HBI of 0.97 while that of Anopheles arabiensis collected at Ahero was 0.23. However, the HBI of A. arabiensis varied depending on the availability of outdoor resting shelters. Most female A. arabiensis (98.9%) collected outdoors in granaries at Ahero had fed on cattle. Indoor-collected female Anopheles funestus had mainly fed on people (93.0%), but taken at least some of their blood (20.2%) from cattle. Although small numbers of A. arabiensis fed on sheep or goats and birds, none of the female A. gambiae s.s. and A. funestus tested had fed on these hosts. The absence of human-fed A. arabiensis in outdoor shelters indicated that exiting after feeding, a behaviour pattern that mitigates indoor insecticidal spraying, is not prevalent in this species in western Kenya.

Plasmodium falciparum sporozoite and entomological inoculation rates at the Ahero rice irrigation scheme and the Miwani sugar-belt in western Kenya.

Anopheles arabiensis and An. funestus were collected by pyrethrum spray sheet collections in houses and by human-bait catches at a village in western Kenya adjacent to the Ahero rice irrigation scheme; and using the same methods, An. gambiae s.l. and An. funestus were collected at Miwani, a village in the sugar-cane belt. Plasmodium falciparum sporozoite rates were determined by ELISA. At Ahero the mean sporozoite rates were 1.1% and 4.3% in An. arabiensis and An. funestus, respectively, while at Miwani the rates were 6.0% in An. gambiae s.l. and 4.3% in An. funestus. Entomolgoical inoculation rates (EIR) were derived from both human-bait collections (IR-HBC) and by the proportion of human blood-fed females caught resting indoors (IR-HBF). The IR-HBF appeared to be a more realistic index of EIR. At Ahero and Miwani people were exposed to an average of 416 and 91 infective bites/person/year, respectively. The main vectors were An. funestus at Ahero and An. gambiae s.l. at Miwani. In view of the intense and perennial malaria transmission at Ahero, vector control by insecticides should be considered, while at Miwani, where transmission is seasonal, permethrin-impregnated bed nets could be an alternative to indoor spraying. These measures must be augmented with availability of effective antimalarials.