Malaria Prevalence among Young Infants in Different Transmission Settings, Africa.

The prevalence and consequences of malaria among infants are not well characterized and may be underestimated. A better understanding of the risk for malaria in early infancy is critical for drug development and informed decision making. In a cross-sectional survey in Guinea, The Gambia, and Benin, countries with different malaria transmission intensities, the overall prevalence of malaria among infants <6 months of age was 11.8% (Guinea, 21.7%; The Gambia, 3.7%; and Benin, 10.2%). Seroprevalence ranged from 5.7% in The Gambia to 41.6% in Guinea. Mean parasite densities in infants were significantly lower than those in children 1-9 years of age in The Gambia (p<0.0001) and Benin (p = 0.0021). Malaria in infants was significantly associated with fever or recent history of fever (p = 0.007) and anemia (p = 0.001). Targeted preventive interventions, adequate drug formulations, and treatment guidelines are needed to address the sizeable prevalence of malaria among young infants in malaria-endemic countries.

Submicroscopic infections with Plasmodium falciparum during pregnancy and their association with circulating cytokine, chemokine, and cellular profiles.

The immunological consequences of pregnancy-associated malaria (PAM) due to Plasmodium falciparum have been extensively investigated in cross-sectional studies conducted at delivery, but there have been very few longitudinal studies of changes due to PAM during pregnancy. We conducted a prospective study in Benin to investigate the changes associated with PAM in groups of 131 and 111 women at inclusion in the second trimester and at delivery, respectively. Infected women were identified by standard microscopic examinations of blood smears and by quantitative PCR (qPCR) assays and were matched to uninfected control women by age, gestational age, and gravidity. We quantified plasma levels of a panel of soluble immunological mediators and other mediators, as well as the frequencies of peripheral blood mononuclear cell types. Comparisons of these variables in infected and uninfected women used multivariate analyses, and we also assessed the predictive value of variables measured at inclusion for pregnancy outcomes at delivery. In multivariate analyses, peripheral plasma interleukin 10 (IL-10) and gamma interferon-inducible protein 10 (IP-10) levels were associated with PAM at inclusion and at delivery, while higher IL-10 levels distinguished qPCR-detectable submicroscopic infections at inclusion but not at delivery. Maternal anemia at delivery was associated with markers of proinflammatory (increased frequency of monocytes) and anti-inflammatory (increased IL-10 levels and increased activation of regulatory T cells) activity measured at inclusion. Elevated concentrations of IL-10 are associated with the majority of P. falciparum infections during pregnancy, but this marker alone does not identify all submicroscopic infections. Reliably identifying such occult infections will require more sensitive and specific methods.

Peripheral blood cell signatures of Plasmodium falciparum infection during pregnancy.

Sequestration of Plasmodium falciparum-infected erythrocytes in placental intervillous spaces causes inflammation and pathology. Knowledge of the profiles of immune cells associated with the physiopathology of pregnancy-associated malaria (PAM) is scarce. We conducted a longitudinal, prospective study, both in Benin and Tanzania, including ∼1000 pregnant women in each site with systematic follow-up at scheduled antenatal visits until delivery. We used ex vivo flow cytometry to identify peripheral blood mononuclear cell (PBMC) profiles that are associated with PAM and anaemia, determining the phenotypic composition and activation status of PBMC in selected sub-groups with and without PAM both at inclusion and at delivery in a total of 302 women. Both at inclusion and at delivery PAM was associated with significantly increased frequencies both of B cells overall and of activated B cells. Infection-related profiles were otherwise quite distinct at the two different time-points. At inclusion, PAM was associated with anaemia, with an increased frequency of immature monocytes and with a decreased frequency of regulatory T cells (Treg). At delivery, infected women presented with significantly fewer plasmacytoid dendritic cells (DC), more myeloid DC expressing low levels of HLA-DR, and more effector T cells (Teff) compared to uninfected women. Independent associations with an increased risk of anaemia were found for altered antigen-presenting cell frequencies at inclusion, but for an increased frequency of Teff at delivery. Our findings emphasize the prominent role played by B cells during PAM whenever it arises during pregnancy, whilst also revealing signature changes in other circulating cell types that, we conclude, primarily reflect the relative duration of the infections. Thus, the acute, recently-acquired infections present at delivery were marked by changes in DC and Teff frequencies, contrasting with infections at inclusion, considered chronic in nature, that were characterized by an abundance of immature monocytes and a paucity of Treg in PBMC.

Spontaneous postpartum clearance of Plasmodium falciparum parasitemia in pregnant women, Benin.

The question of malaria in the postpartum period is controversial. Malaria was investigated during a randomized trial of intermittent preventive treatment in pregnancy in Benin. Women infected at delivery were tested for parasitemia in the early postpartum period; they had not received treatment unless they were symptomatic. Among the 35 of 1,346 infected women, parasitologic follow-up results could not be interpreted in 15 because they were treated for symptoms, 18 cleared parasitemia spontaneously within five days postpartum, and 2 had a strong decrease in parasitemia before being treated. Because the placenta is the privileged site for sequestration of parasites, it facilitates their persistence during pregnancy, and its elimination may rapidly induce their clearance.

Adding artesunate to sulphadoxine-pyrimethamine greatly improves the treatment efficacy in children with uncomplicated falciparum malaria on the coast of Benin, West Africa.

BACKGROUND: Benin has recently shifted its national antimalarial drug policy from monotherapies to combinations containing artemisinin derivatives. When this decision was taken, the available information on alternatives to chloroquine and sulphadoxine-pyrimethamine, the first- and second-line treatment, was sparse. METHODS: In 2003 - 2005, before the drug policy change, a randomized, open-label, clinical trial was carried out on the efficacy of chloroquine, and sulphadoxine-pyrimethamine alone or combined with artesunate, with the aim of providing policy makers with the information needed to formulate a new antimalarial drug policy. Children between six and 59 months of age, with uncomplicated malaria and living in the lagoon costal area in southern Benin, were randomly allocated to one of the three study arms and followed up for 28 days. RESULTS: Treatment failure (PCR corrected) was significantly lower in the artesunate + sulphadoxine-pyrimethamine group (4/77, 5.3%) than in chloroquine group(51/71, 71.8%) or the sulphadoxine-pyrimethamine alone group (30/70, 44.1%) (p < 0.001). Despite high sulphadoxine-pyrimethamine failure, its combination with artesunate greatly improved treatment efficacy. CONCLUSION: In Benin, artesunate + sulphadoxine-pyrimethamine is efficacious and could be used when the recommended artemisinin-based combinations (artemether-lumefantrine and amodiaquine-artesunate) are not available. However, because sulphadoxine-pyrimethamine is also used in pregnant women as intermittent preventive treatment, its combination with artesunate should not be widely employed in malaria patients as this may compromise the efficacy of intermittent preventive treatment.