Abstract
Approximately 3.2 billion people live in areas where malaria is endemic, and WHO estimates that 350 to 500 million malaria cases occur each year worldwide. This high prevalence, and the high frequency of international travel, creates significant risk for the exportation of malaria to countries where malaria is not endemic and for the introduction of malaria organisms into the blood supply. Since all four human infectious Plasmodium species have been transmitted by blood transfusion, we sought to develop an enzyme-linked immunosorbent assay (ELISA) capable of detecting antibodies elicited by infection with any of these species. The merozoite surface protein 1 (MSP1), a P. falciparum and P. vivax vaccine candidate with a well-characterized immune response, was selected for use in the assay. The MSP1 genes from P. ovale and P. malariae were cloned and sequenced (L. Birkenmeyer, A. S. Muerhoff, G. Dawson, and S. M. Desai, Am. J. Trop. Med. Hyg. 82:996-1003, 2010), and the carboxyl-terminal p19 regions of all four species were expressed in Escherichia coli. Performance results from individual p19 ELISAs were compared to those of a commercial test (Lab 21 Healthcare Malaria enzyme immunoassay [EIA]). The commercial ELISA detected all malaria patients with P. falciparum or P. vivax infections, as did the corresponding species-specific p19 ELISAs. However, the commercial ELISA detected antibodies in 0/2 and 5/8 individuals with P. malariae and P. ovale infections, respectively, while the p19 assays detected 100% of individuals with confirmed P. malariae or P. ovale infections. In experimentally infected nonhuman primates, the use of MSP1-p19 antigens from all four species resulted in the detection of antibodies within 2 to 10 weeks postinfection. Use of MSP1-p19 antigens from all four Plasmodium species in a single immunoassay would provide significantly improved efficacy compared to existing tests.