DETECTION OF SPOROZOITES OF PLASMODIUM-VIVAX AND PLASMODIUM-FALCIPARUM IN MOSQUITOS BY ELISA - FALSE POSITIVITY ASSOCIATED WITH BOVINE AND SWINE BLOOD

Blood samples from cows and pigs were tested for possible cross-reacti vity with a monoclonal antibody-based enzyme-linked immunosorbent assa y (ELISA) kit designed for detection of human malaria sporozoites in m osquitoes. The results revealed that 4 of 16 cows (25%) reacted positi vely with both Plasmodium falciparum (2A10) and P. vivax (NSV3) monocl onal antibodies and 8 (50%) were positive with NSV3 only. One of 12 pi gs (8.33%) was positive with both antibodies, and 2 (16.6%) were posit ive with NSV3 only. The positivity was associated with plasma, but not with the blood cell fraction. Antigenic extracts of Sarcocystis, Toxo plasma gondii and Trypanosoma evansi gave negative ELISA results, sugg esting that these were not the factors in animal blood which gave posi tive results. Laboratory Anopheles dirus A fed on blood of a positive cow by membrane feeding also gave a positive ELISA result. Furthermore , some blood-fed culicine mosquitoes collected directly from a positiv e cow were ELISA-positive. The cross-reactive factor(s) in plasma has (have) not yet been identified. These false positive ELISA results cou ld complicate the assessment of sporozoite rate in mosquito population s if the study were carried out by ELISA only, especially in areas whe re cattle and swine are present.