Detection and quantification of Plasmodium falciparum and P. vivax infections in Thai-Kampuchean Anopheles (Diptera: Culicidae) by enzyme-linked immunosorbent assay.

Abstract

Enzyme-linked immunosorbent assays (ELISA's) were used to identify Plasmodium falciparum (Welch) and Plasmodium vivax (Grassi & Feletti) infections in 13 Anopheles species collected in the Thailand–Kampuchea border area. ELISA tests on 1,680 mosquitoes detected P. falciparum infections in nine species and P. vivax infections in four species. ELISA tests on 325 mosquitoes divided at the thorax indicated that 10 of 21 infected mosquitoes contained midgut infections in the absence of salivary gland infections. Based on relative abundances of species collected and infection rates detected, Anopheles aconitus Donitz, Anopheles annularis Van der Wulp, Anopheles barbirostris Van der Wulp group, Anopheles peditaeniatus (Leicester), and Anopheles vagus Donitz should be considered as potential important vectors of malaria in the situations described, but vector status of these species requires confirmation. A sporozoite quantification method was developed and used to estimate infection levels in individual mosquitoes. Circumsporozoite (CS) protein levels equivalent to >2,000 sporozoites per mosquito were detected in one out of two infected Anopheles dirus Peyton & Harrison and most infected A. annularis, but CS protein levels equivalent to <275 sporozoites per mosquito were detected in 50% of infections in all species. In general, mosquitoes with P. falciparum infections contained more CS protein than those infected with P. vivax.