ABSTRACT
In support of ongoing immunologic studies on immunity to Plasmodium falciparum, demographic, entomologic, parasitologic, and clinical studies were conducted in two Cameroonian villages located 3 km apart. Simbok (population = 907) has pools of water present year round that provide breeding sites for Anopheles gambiae, whereas Etoa (population = 485) has swampy areas that dry up annually in which A. funestus breed. Results showed that individuals in Simbok receive an estimated 1.9 and 1.2 infectious bites per night in the wet and dry season, respectively, whereas individuals in Etoa receive 2.4 and 0.4 infectious bites per night, respectively. Although transmission patterns differ, the rate of acquisition of immunity to malaria appears to be similar in both villages. A prevalence of 50-75% was found in children < 10 years old, variable levels in children 11-15 years old, and 31% in adults. Thus, as reported in other parts of Africa, individuals exposed to continuous transmission of P. falciparum slowly acquired significant, but not complete, immunity.
Subject(s)
Anopheles/parasitology , Malaria, Falciparum/epidemiology , Malaria, Falciparum/immunology , Plasmodium falciparum/isolation & purification , Adolescent , Adult , Age Distribution , Aged , Animals , Anopheles/classification , Cameroon/epidemiology , Child , Child, Preschool , Disease Vectors , Female , Humans , Infant , Infant, Newborn , Longitudinal Studies , Malaria, Falciparum/transmission , Male , Middle Aged , Plasmodium falciparum/immunology , Plasmodium falciparum/parasitology , Prevalence , SeasonsABSTRACT
Pregnant women have an increased susceptibility to infection by Plasmodium falciparum. Parasites may 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 peripheral blood smear negative. Thus, malarial infection was not detected by microscopic examination of peripheral blood smears from approximately one out of five malaria-infected women. Since P. falciparum parasites secrete histidine-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 presence of parasites "hidden" in the placenta. Samples of peripheral plasma from 127 women with different levels of placental malarial infection were assayed by HRP-2-specific enzyme-linked immunosorbent assay. HRP-2 was detected in 88% of the women with placental malaria who tested negative by blood smear. Additionally, whole blood was obtained from 181 women and tested for HRP-2 with a rapid, chromatographic strip test (ICT). The ICT test accurately detected malarial infection in 89.1% of P. falciparum-infected women. Furthermore, 94% of women with malaria were accurately diagnosed by using a combination of microscopy and the ICT test. Thus, detection of HRP-2 in conjunction with microscopy should improve diagnosis of malaria in pregnant women.
