Detection of the Plasmodium falciparum antigen histidine-rich protein 2 inblood of pregnant women: Implications for diagnosing placental malaria

Pregnant women have an increased susceptibility to infection by Plasmodium falciparum. Parasites mag be present in the placenta yet not detectable in peripheral blood smears by routine light microscopy. In order to determine how frequently misdiagnosis occurs, peripheral blood and placental samples were collected from 1,077 Cameroonian women at the time of giving birth and examined for the presence of malarial parasites by using light microscopy, Results showed that 20.1% of the women who had placental malaria were peri pheral blood smear negative. Thus, malarial infection,vas not detected by m icroscopic examination of peripheral blood smears from approximately one ou t of five malaria-infected women. Since P. falciparum parasites secrete his tidine-rich protein 2 (HRP-2), we sought to determine if detecting HRP-2 in either peripheral plasma or whole blood might be used to diagnose the pres ence of parasites "hidden" in the placenta. Samples of peripheral plasma fr om 127 women with different levels of placental malarial infection were ass ayed by HRP-2-specific enzyme-linked immunosorbent assay. HRP-2 was detecte d in 88% of the women with placental malaria who tested negative by blood s mear, Additionally, whole blood was obtained from 181 women and tested for HRP-2 with a rapid, chromatographic strip test (ICT). The ICT test accurate ly detected malarial infection in 89.1% of P. falciparum-infected women. Fu rthermore, 94% of women with malaria were accurately diagnosed by using a c ombination of microscopy and the ICT test. Thus, detection of HRP-2 in conj unction with microscopy should improve diagnosis of malaria in pregnant wom en.