High Prevalence Of Antibody Response Against Plasmodium Falciparum (Pf) Antigens In A Holoendemic Area Of Benin (1994-1995)

The present study aimed at measuring the capacity of naturally occurring antibodies to bind Pf83/AMA-1 and MSP-1/19 antigens, two malaria vaccine candidates, in an immunoassay. According to the fact that antibody prevalence reflects endemicity of malaria, we further aimed at using the results obtained here as baseline data set to follow up and evaluate the expected decline in endemicity in 2016, 8 years after the change in drug policy in Benin. Therefore, individuals, 2 – 19 and above 20 years old, living in Awansori, a malaria holoendemic area in the suburb of Cotonou, Benin were bled during the dry and raining seasons of the years 1994/1995. Antibody responses were measured using direct, indirect and competition ELISA. We found a very high prevalence of antibody responses (89 to 96%) in the studied population. The results indicate for Pf83/AMA-1, that naturally occurring antibodies bind to protective epitopes in a competition ELISA with a parasite inhibiting monoclonal antibody. The data and samples analysed here were collected during the rainy season 1994 and the following dry season 1994/1995

Human saliva as a source of anti-malarial antibodies to examine population exposure to Plasmodium falciparum

BACKGROUND: Antibody responses to malaria antigens reflect exposure to parasites, and seroprevalence correlates with malaria transmission intensity. Antibodies are routinely measured in sera or on dried blood spots but a non-invasive method would provide extra utility in sampling general populations. Saliva is already in use in the detection of plasma-derived IgM and IgG to viral infections. In this study, antibodies to Plasmodium falciparum merozoite antigens were compared between blood and saliva samples from the same individuals in unlinked surveys conducted in Tanzania and The Gambia. METHODS: In Tanzania, 53 individuals provided paired fingerprick blood and saliva sample using two commercially available sampling devices. In the Gambia, archived plasma and saliva samples collected from 200 children in the Farafenni area in a cross-sectional survey were analyzed.IgG antibodies against P. falciparum antigens, Merozoite Surface Protein-1 (MSP-119) and Apical membrane Antigen (AMA-1) were measured by ELISA in paired saliva and blood samples from both sites. Antibody levels were compared as continuous optical density (OD) values and by sero-positivity. RESULTS: Significant correlations between saliva and plasma antibody levels were seen in Tanzania for both antigens, AMA-1(r2 range 0.93 to 0.89, p < 0.001) and MSP-119 (r2 range 0.93 to 0.75, p < 0.001), with a weaker correlation for results from The Gambia (r2range 0.64 to 0.63, p < 0.01). When assessed as seropositivity and compared with plasma, sensitivity and specificity were good with saliva antibody levels to both AMA-1 and MSP-1(19) (sensitivity range 64-77% and specificity range 91-100% & 47-67% and 90-97% respectively) over the different sample sets. CONCLUSIONS: These data demonstrate anti-malarial antibodies can be detected in saliva and correlate strongly with levels in plasma. This non-invasive relatively simple collection method will be potentially useful for general population surveys, and particularly in migratory populations or those with infrequent contact with health services or opposed to blood withdrawal. Further studies will be needed to optimize collection methods, standardize volumes and content and develop controls

Comparison of surveillance methods applied to a situation of low malaria prevalence at rural sites in The Gambia and Guinea Bissau

BACKGROUND: Health record-based observations from several parts of Africa indicate a major decline in malaria, but up-to-date information on parasite prevalence in West-Africa is sparse. This study aims to provide parasite prevalence data from three sites in the Gambia and Guinea Bissau, respectively, and compares the usefulness of PCR, rapid diagnostic tests (RDT), serology and slide-microscopy for surveillance. METHODS: Cross-sectional surveys in 12 villages at three rural sites were carried out in the Gambia and Guinea Bissau in January/February 2008, shortly following the annual transmission season. RESULTS: A surprisingly low microscopically detectable parasite prevalence was detected in the Gambia (Farafenni: 10.9%, CI95%: 8.7-13.1%; Basse: 9.0%, CI95%: 7.2-10.8%), and Guinea Bissau (Caio: 4%, CI95%: 2.6-5.4%), with low parasite densities (geometric mean: 104 parasites/microl, CI95%: 76-143/microl). In comparison, PCR detected a more than three times higher proportion of parasite carriers, indicating its usefulness to sensitively identify foci where malaria declines, whereas the RDT had very low sensitivity. Estimates of force of infection using age sero-conversion rates were equivalent to an EIR of approximately 1 infectious bite/person/year, significantly less than previous estimates. The sero-prevalence profiles suggest a gradual decline of malaria transmission, confirming their usefulness in providing information on longer term trends of transmission. A greater variability in parasite prevalence among villages within a site than between sites was observed with all methods. The fact that serology equally captured the inter-village variability, indicates that the observed heterogeneity represents a stable pattern. CONCLUSION: PCR and serology may be used as complementary tools to survey malaria in areas of declining malaria prevalence such as the Gambia and Guinea Bissau

A Decline in the Incidence of Invasive Non-Typhoidal Salmonella Infection in the Gambia Temporally Associated with a Decline in Malaria Infection

BACKGROUND: Malaria is a risk factor for invasive non-typhoidal Salmonella (NTS) infection in children. In the last 10 years, indices of malaria infection in The Gambia have fallen substantially. METHODS: We compared temporal trends of childhood malaria and NTS infection in two Gambian locations. In Fajara, on the coast, the incidence of NTS infection at three time points between 1979 and 2005 was compared to the percentage of malaria positive outpatient thick blood films and the percentage of admissions associated with malaria over time. In Basse, in the eastern part of the country, the incidence of NTS infection at three time points between 1989 and 2008 was compared to the prevalence of malaria parasitaemia at four time points between 1992 and 2008. RESULTS: The estimated incidence of NTS infection in Fajara fell from 60 (1979-1984) to 10 (2003-05) cases per 100,000 person years. The proportion of outpatients in Fajara with suspected malaria who were parasitaemic fell from 33% (1999) to 6% (2007) while the proportion of admissions associated with malaria fell from 14.5% (1999) to 5% (2007). In Basse, the estimated incidence of NTS infection fell from 105 (1989-1991) to 29 (2008) cases per 100,000 person years while the prevalence of malaria parasitaemia fell from 45% (1992) to 10% (2008). The incidence of pneumococcal bacteraemia in Fajara and Basse did not fall over the study period. CONCLUSIONS: These data support an association between malaria and NTS infection. Reductions in malaria infection may be associated with reduced rates of invasive childhood NTS infection

A Decline in the Incidence of Invasive Non-Typhoidal Salmonella Infection in the Gambia Temporally Associated with a Decline in Malaria Infection

BACKGROUND: Malaria is a risk factor for invasive non-typhoidal Salmonella (NTS) infection in children. In the last 10 years, indices of malaria infection in The Gambia have fallen substantially. METHODS: We compared temporal trends of childhood malaria and NTS infection in two Gambian locations. In Fajara, on the coast, the incidence of NTS infection at three time points between 1979 and 2005 was compared to the percentage of malaria positive outpatient thick blood films and the percentage of admissions associated with malaria over time. In Basse, in the eastern part of the country, the incidence of NTS infection at three time points between 1989 and 2008 was compared to the prevalence of malaria parasitaemia at four time points between 1992 and 2008. RESULTS: The estimated incidence of NTS infection in Fajara fell from 60 (1979-1984) to 10 (2003-05) cases per 100,000 person years. The proportion of outpatients in Fajara with suspected malaria who were parasitaemic fell from 33% (1999) to 6% (2007) while the proportion of admissions associated with malaria fell from 14.5% (1999) to 5% (2007). In Basse, the estimated incidence of NTS infection fell from 105 (1989-1991) to 29 (2008) cases per 100,000 person years while the prevalence of malaria parasitaemia fell from 45% (1992) to 10% (2008). The incidence of pneumococcal bacteraemia in Fajara and Basse did not fall over the study period. CONCLUSIONS: These data support an association between malaria and NTS infection. Reductions in malaria infection may be associated with reduced rates of invasive childhood NTS infection

Prevalence De L’anemie Et Des Anticorps Specifiques Anti-P. Falciparum Chez Les PVVIH Et Co-Infectees Par Le Plasmodium Falciparum Au Congo-Brazzaville

HIV and P. falciparum lead to diseases with overlapping endemic areas. Both diseases are leading cause of nearly 2 millions of deaths each year, which occur mostly in developing countries. People living with HIV are more susceptible to disease progressions. It is therefore important to further understand the biology of HIV and P. falciparum coinfection. The present study sets to characterize the coinfection with regard to malaria specific antibodies and to anemia. We found that antibody and hemoglobin levels as well as CD4 counts differ significantly according to parasite load and to treatment with anti retroviral. People undergoing treatment with antiretroviral, produced specific antimalarial IgG compared to their treatment naïve counterparts

Population genetic structure of Plasmodium falciparum across a region of diverse endemicity in West Africa.

BACKGROUND: Malaria parasite population genetic structure varies among areas of differing endemicity, but this has not been systematically studied across Plasmodium falciparum populations in Africa where most infections occur. METHODS: Ten polymorphic P. falciparum microsatellite loci were genotyped in 268 infections from eight locations in four West African countries (Republic of Guinea, Guinea Bissau, The Gambia and Senegal), spanning a highly endemic forested region in the south to a low endemic Sahelian region in the north. Analysis was performed on proportions of mixed genotype infections, genotypic diversity among isolates, multilocus standardized index of association, and inter-population differentiation. RESULTS: Each location had similar levels of pairwise genotypic diversity among isolates, although there were many more mixed parasite genotype infections in the south. Apart from a few isolates that were virtually identical, the multilocus index of association was not significant in any population. Genetic differentiation between populations was low (most pairwise F(ST) values < 0.03), and an overall test for isolation by distance was not significant. CONCLUSIONS: Although proportions of mixed genotype infections varied with endemicity as expected, population genetic structure was similar across the diverse sites. Very substantial reduction in transmission would be needed to cause fragmented or epidemic sub-structure in this region