Submicroscopic Plasmodium falciparum infections and multiplicity of infection in matched peripheral, placental and umbilical cord blood samples from Gabonese women

Abstract

SummaryIn malaria-endemic regions, pregnant women are more susceptible to malarial infections than nonpregnant women. The main objective of this study, which was conducted in the malaria hyperendemic town of Lambaréné (Gabon, Central Africa), was to characterize Plasmodium falciparum infections in peripheral, placental and cord blood from women of different gravidities with submicroscopic infections. Using the P. falciparum merozoite surface protein 2 (MSP 2)* gene as a polymorphic marker in polymerase chain reactions, we analysed genetic diversity and multiplicity of infection in isolates from all three kinds of samples of 184 pregnant women at delivery. We detected infection in 44% of the women who were originally negative by microscopy. Equally important was the finding that the placenta had the highest prevalence of infection (P < 0.001). There was no correlation with gravidity status or age of the patients. The multiplicities of infection in the peripheral and placental blood samples did not differ and single infection was observed in cord blood, independently of the gravidity. The FC27/MSP 2 was the predominant allelic family. The major FC27 alleles detected in the peripheral, placental and cord blood were sequenced and found to be closely related to the published K1 form sequence. Below microscopy level, the placenta remains the most infected organ and this submicroscopic carriage of parasites may contribute to the development and maintenance of immunity to malaria during pregnancy.keywords MSP 2 marker, polymerase chain reaction, submicroscopic infections, multiplicity of infections

Longitudinal Studies of Plasmodium falciparum Malaria in Pregnant Women Living in a Rural Cameroonian Village with High Perennial Transmission

“…As previously reported, submicroscopic infections are common in pregnant women, 19,21,22 as well as the presence of multiple parasite genotypes. 19,[22][23][24] The number of genotypes has been found to decrease with gravidity in some studies, 23,24 but not in others.…”

“…19,20 This assay is a standard approach for studying genetic diversity of P. falciparum , 18,20 including in pregnant women. 19,[21][22][23][24][25] The number of alleles at the two loci was determined and the locus with the largest number of bands was used to estimate the MoI. In addition, the C-terminus of MSP-1 was sequenced and the MSP1-19 type was determined based on amino acids at position 294, 341, 349, 350, 351, and 366 of the MSP-1 42 3D7 reference sequence.…”

Persistence of Plasmodium falciparum Parasites in Infected Pregnant Mozambican Women after Delivery

“…Moreover, 43% of the women had peripheral parasitemia with genotypes that were not found in their placental blood. Although discrepancies between genotypes (18,19,25,38) might also be explained by synchronicity of infections (10) or by inconsistent detection of parasites at low densities (27), these results suggest that parasites adhering to other receptors apart from those specifically displayed in the placenta might be the ones that persist after delivery. Further studies evaluating the adhesive phenotype of persisting parasites would be of great utility to better understand the pathophysiology of maternal infections.…”

“…Moreover, infections at densities below the limit of microscopic detection (submicroscopic infections) contribute to the underestimation of the actual burden of P. falciparum infection among pregnant women in areas where malaria is endemic (25,28,37). The PCR method has the potential to overcome these limitations by providing a more sensitive estimate of maternal infections (44).…”

Distinct Th1- and Th2-Type Prenatal Cytokine Responses toPlasmodium falciparumErythrocyte Invasion Ligands

“…Rates of 14 to 33 percent have been reported when more-sensitive diagnostic methods, such as PCR or circulating parasite antigen assays, are used (27,28,57,61). Current evidence suggests that admixture of the maternal and fetal circulations at the time the newborn is passing through the birth canal is uncommon, since malaria genotypes examined in matched cord and maternal blood samples are often discordant with maternal peripheral blood (27,28,40,57) or placental intervillous blood (27), and maternal IgE that does not cross the placenta is rarely detected in cord blood (30). Third, studies of rodent malarias demonstrate that prenatal T-cell sensitization occurs when pregnant rats are infected with Plasmodium berghei (10,11,(13)(14)(15).…”