Identification of malaria species by ELISA in sporozoite and oocyst infected Anopheles from western Kenya.

Enzyme-linked immunosorbent assays (ELISAs) for the circumsporozoite (CS) antigens of Plasmodium falciparum, P. malariae, and P. ovale were used to identify species of sporozoite and oocyst infections detected by dissection in Anopheles gambiae s.1. and An. funestus collected in western Kenya. ELISAs identified 92.5% of 1,113 salivary gland infections; Plasmodium species infections included 79.4% P. falciparum, 3.2% P. malariae, 1.7% P. ovale, and 2 or more Plasmodium species were detected in 15.7% of the Anopheles in which the species of parasite was identified. Identification was more likely with greater numbers of sporozoites observed in dissections, increasing from 65% ELISA positivity in mosquitoes with 1-10 sporozoites in their salivary glands to 96% in mosquitoes with over 1,000 sporozoites. ELISAs detected CS antigen in 66% of 294 Anopheles that by dissection had oocysts but uninfected salivary glands. Of 112 Anopheles with a single species of Plasmodium detected in the salivary glands, 29 (25.9%) had 1 or more additional species detected in the midgut, indicating a high potential for multiple infections. Similar proportions of Plasmodium species were found in An. gambiae s.1. and An. funestus.