Dynamics and role of antibodies to Plasmodium falciparum merozoite antigens in children living in two settings with differing malaria transmission intensity

AbstractBackgroundYoung infants have reduced susceptibility to febrile malaria compared with older children, but the mechanism for this remains unclear. There are conflicting data on the role of passively acquired antibodies. Here, we examine antibody titres to merozoite surface antigens in the protection of children in their first two years of life in two settings with differing malaria transmission intensity and compare these titres to previously established protective thresholds.MethodsTwo cohorts of children aged four to six weeks were recruited in Banfora, Burkina and Keur Soce, Senegal and followed up for two years. Malaria infections were detected by light microscopic examination of blood smears collected at active and passive case detection visits. The titres of antibodies to the Plasmodium falciparum recombinant merozoite proteins (AMA1-3D7, MSP1-19, MSP2-Dd2, and MSP3-3D7) were measured by enzyme-linked immunosorbent assay at 1–6, 9, 12, 15 and 18 months of age and compared with the protective thresholds established in Kenyan children.ResultsAntibody titres were below the protective thresholds throughout the study period and we did not find any association with protection against febrile malaria. Antibodies to AMA1 and MSP1-19 appeared to be markers of exposure in the univariate analysis (and so associated with increasing risk) and adjusting for exposure reduced the strength and significance of this association.ConclusionThe antibody levels we measured are unlikely to be responsible for the apparent protection against febrile malaria seen in young infants. Further work to identify protective antibody responses might include functional assays and a wider range of antigens

Inherited Disorders of Hemoglobin and <em>Plasmodium falciparum</em> Malaria

An estimated 300,000 babies are born each year with severe Inherited Disorders of Hemoglobin (IDH). Despite major advances in the understanding of the molecular pathology, control, and management of the IDH thousands of infants and children with these diseases are dying due to the accessibility to appropriate medical care. In addition, as malaria has been the principal cause of early mortality in several parts of the world for much of the last 5000 years, as a result, it is the strongest force for selective pressure on the human genome. That is why, in the world, there is an overlap of malaria endemicity and IDH. Over the past twenty years several studies have shown that IDH such us hemoglobin and/or red cell membrane abnormalities confer resistance to malaria reducing hence the mortality during the first years of life. This has led to the selection of populations with IDH in malaria-endemic areas. This may explain the overlap between these two pathologies. This chapter aims to present the relationship between IDH and malaria susceptibility, make an overview of the current state of knowledge and the burden of IDH, and highlight steps that require to be taken urgently to improve the situation

The ABO Blood Group System and <em>Plasmodium falciparum</em> (<em>Pf </em>) Infection in Three Ethnic Groups Living in the Stable and Seasonal Malaria Transmission Areas of Burkina Faso (BF)

Genetic factors, including red blood cell polymorphisms, influence the severity of disease due to infection with Plasmodium falciparum (Pf). Studies show that these genetic factors associated with malaria susceptibility or resistance vary geographically, ethnically, and racially. We performed cross-sectional surveys in population living in rural villages from three ethnic groups. The blood group (BG) was determined genetically using two polymorphisms (rs8176719 and rs8176746). Out of 548 participants, 29.7% were Mossi, 38.2% were Fulani, and 32.1% were Rimaibe. The distribution of BG was, respectively, A: 25.5%, B: 26.6%, AB: 7.3%, and O: 40.5%. BG O was not only the common blood type overall, but was higher in Fulani (52.6%) than others. Fulani was associated with a reduced risk of infection and lower parasite densities than sympatric populations. The subjects with non-O blood were less susceptible to malaria infection. An association between ethnicity and malaria infection during the high transmission season as well as an association between the non-O blood group and malaria infections according to ethnicity was found. This was also true when ethnic groups were considered separately. Our results have demonstrated that the Fulani are not only less susceptible to Pf malaria infection, but when infected have lower parasite densities. Individuals with non-O blood are at lower risk of infection

Early treatment of childhood fevers with pre-packaged antimalarial drugs in the home reduces severe malaria morbidity in Burkina Faso.

In rural, malaria-endemic Burkina Faso, we evaluated the impact of the use of pre-packaged antimalarial drugs (PPAM), by mothers in the home, on the progression of disease in children from uncomplicated fever to severe malaria. In each village of one province, a core group of opinion leaders (mainly older mothers) was trained in the management of uncomplicated malaria, including the administration of PPAM. Full courses of antimalarial (chloroquine) and antipyretic (aspirin) drugs were packaged in age-specific bags and made widely available through community health workers who were supplied through the existing drug distribution system. Drugs were sold under a cost-recovery scheme. Local schoolteachers conducted surveys in a random sample of 32 villages at the end of the high transmission seasons in 1998 and 1999. Disease history and the treatment received were investigated for all children under the age of 6 years having suffered from a fever episode in the previous 4 weeks. 'Uncomplicated malaria' was defined as every episode of fever and 'severe malaria' as every episode of fever followed by convulsions or loss of consciousness. During the study period, 56%[95% confidence interval (CI) 50-62%] of 3202 fever episodes in children under 6 years of age were treated promptly by mothers with the pre-packaged drugs made available by the study. A total of 59% of children receiving PPAM were reported to have received the drugs over the prescribed 3-day period, while 52% received the correct age-specific dose. PPAM use was similar among literate (61%) and non-literate mothers (55%) (P = 0.08). The overall reported risk of developing severe malaria was 8%. This risk was lower in children treated with PPAM (5%) than in children not treated with PPAM (11%) (risk ratio = 0.47; 95% CI 0.37, 0.60; P < 0.0001). This estimate of the impact of PPAM was largely unchanged when account was taken of potential confounding by age, sex, maternal literacy status, year or village. Our findings support the view that, after appropriate training and with adequately packaged drugs made available, mothers can recognize and treat promptly and correctly malarial episodes in their children and, by doing so, reduce the incidence of severe disease

illustrative case 3: a febrile adult in the dry season.

<p>The pre test probability is at 2%, a positive RDT will never reach the decision threshold at 52.6 since its positive likelihood ratio is only 4.43.</p

The (unique) treatment threshold (or decision threshold).

<p>The (unique) treatment threshold (or decision threshold).</p

IL4-589C/T polymorphism and IgE levels in severe malaria.

Previous studies identified an allelic variant of the IL4 promoter region (IL4-589T) that appears to enhance the transcriptional activity of IL4, and is associated with increased IgE levels. Total serum IgE levels are elevated in malaria endemic regions, and higher in children with severe malaria. Here, we investigated the relationship of the IL4-589C/T polymorphism with severity of the disease in a case-control study of severe malaria in Burkina Faso, West Africa. No association between the IL4-589T and severe malaria was observed. No difference in Plasmodium falciparum-specific IgE was detected between severe and uncomplicated malaria patients. Among children with severe malaria, total IgE levels were significantly elevated in those carrying the IL4-589T allele (P = 0.018). In children with uncomplicated malaria, no significant difference was found. These results raise the possibility that there is a relationship between susceptibility to severe malaria, IgE production and genetic variation in the IL4 region, which merits further investigation in other epidemiological settings