Antibody response to Schistosoma haematobium and other helminth species in malaria-exposed populations from Burkina Faso.

Infection with helminths in sub-Saharan Africa could modulate the immune response towards Plasmodium falciparum as well as susceptibility to malaria infection and disease. The aim of this study is to assess the antibody responses to helminths species in malaria-exposed populations from Burkina Faso. Plasma samples were collected in rural villages inhabited by Fulani, Mossi and Rimaibe communities, and IgG against parasitic helminths were measured by ELISA. The prevalence of IgG against antigens of Strongyloides stercoralis, Wuchereria bancrofti and Schistosoma haematobium (Soluble Egg Antigen, SEA) was 5%, 16% and 63% respectively, in line with estimates of infection prevalence in the region for the three parasites. Anti-SEA IgG prevalence was highest at 10-20 years of age, higher in males than females, and did not show differences between ethnic groups. However, the Fulani showed lower levels of anti-SEA IgG suggesting that lighter S. haematobium infections may occur in the ethnic group known for a marked lower susceptibility to P. falciparum. The present data support the use of serological methods for integrated surveillance of neglected tropical diseases such as soil-transmitted helminths, lymphatic filariasis and bilharzia. Furthermore, as helminth infections might promote downregulation of immune responses against intracellular pathogens, the observation of lower anti-SEA IgG levels in the malaria resistant Fulani population warrants further investigation into the immunological cross-talk between S. haematobium and P. falciparum in this geographical region.

The establishment of a WHO Reference Reagent for anti-malaria (Plasmodium falciparum) human serum.

BACKGROUND: At a World Health Organization (WHO) sponsored meeting it was concluded that there is an urgent need for a reference preparation that contains antibodies against malaria antigens in order to support serology studies and vaccine development. It was proposed that this reference would take the form of a lyophilized serum or plasma pool from a malaria-endemic area. In response, an immunoassay standard, comprising defibrinated human plasma has been prepared and evaluated in a collaborative study. RESULTS: A pool of human plasma from a malaria endemic region was collected from 140 single plasma donations selected for reactivity to Plasmodium falciparum apical membrane antigen-1 (AMA-1) and merozoite surface proteins (MSP-119, MSP-142, MSP-2 and MSP-3). This pool was defibrinated, filled and freeze dried into a single batch of ampoules to yield a stable source of naturally occurring antibodies to P. falciparum. The preparation was evaluated by an enzyme-linked immunosorbent assay (ELISA) in a collaborative study with sixteen participants from twelve different countries. This anti-malaria human serum preparation (NIBSC Code: 10/198) was adopted by the WHO Expert Committee on Biological Standardization (ECBS) in October 2014, as the first WHO reference reagent for anti-malaria (Plasmodium falciparum) human serum with an assigned arbitrary unitage of 100 units (U) per ampoule. CONCLUSION: Analysis of the reference reagent in a collaborative study has demonstrated the benefit of this preparation for the reduction in inter- and intra-laboratory variability in ELISA. Whilst locally sourced pools are regularly use for harmonization both within and between a few laboratories, the presence of a WHO-endorsed reference reagent should enable optimal harmonization of malaria serological assays either by direct use of the reference reagent or calibration of local standards against this WHO reference. The intended uses of this reference reagent, a multivalent preparation, are (1) to allow cross-comparisons of results of vaccine trials performed in different centres/with different products; (2) to facilitate standardization and harmonization of immunological assays used in epidemiology research; and (3) to allow optimization and validation of immunological assays used in malaria vaccine development.

Genetic determinants of anti-malarial acquired immunity in a large multi-centre study.

BACKGROUND: Many studies report associations between human genetic factors and immunity to malaria but few have been reliably replicated. These studies are usually country-specific, use small sample sizes and are not directly comparable due to differences in methodologies. This study brings together samples and data collected from multiple sites across Africa and Asia to use standardized methods to look for consistent genetic effects on anti-malarial antibody levels. METHODS: Sera, DNA samples and clinical data were collected from 13,299 individuals from ten sites in Senegal, Mali, Burkina Faso, Sudan, Kenya, Tanzania, and Sri Lanka using standardized methods. DNA was extracted and typed for 202 Single Nucleotide Polymorphisms with known associations to malaria or antibody production, and antibody levels to four clinical grade malarial antigens [AMA1, MSP1, MSP2, and (NANP)4] plus total IgE were measured by ELISA techniques. Regression models were used to investigate the associations of clinical and genetic factors with antibody levels. RESULTS: Malaria infection increased levels of antibodies to malaria antigens and, as expected, stable predictors of anti-malarial antibody levels included age, seasonality, location, and ethnicity. Correlations between antibodies to blood-stage antigens AMA1, MSP1 and MSP2 were higher between themselves than with antibodies to the (NANP)4 epitope of the pre-erythrocytic circumsporozoite protein, while there was little or no correlation with total IgE levels. Individuals with sickle cell trait had significantly lower antibody levels to all blood-stage antigens, and recessive homozygotes for CD36 (rs321198) had significantly lower anti-malarial antibody levels to MSP2. CONCLUSION: Although the most significant finding with a consistent effect across sites was for sickle cell trait, its effect is likely to be via reducing a microscopically positive parasitaemia rather than directly on antibody levels. However, this study does demonstrate a framework for the feasibility of combining data from sites with heterogeneous malaria transmission levels across Africa and Asia with which to explore genetic effects on anti-malarial immunity.

Human candidate polymorphisms in sympatric ethnic groups differing in malaria susceptibility in Mali.

Malaria still remains a major public health problem in Mali, although disease susceptibility varies between ethnic groups, particularly between the Fulani and Dogon. These two sympatric groups share similar socio-cultural factors and malaria transmission rates, but Fulani individuals tend to show significantly higher spleen enlargement scores, lower parasite prevalence, and seem less affected by the disease than their Dogon neighbours. We have used genetic polymorphisms from malaria-associated genes to investigate associations with various malaria metrics between the Fulanai and Dogon groups. Two cross sectional surveys (transmission season 2006, dry season 2007) were performed. Healthy volunteers from the both ethnic groups (n=939) were recruited in a rural setting. In each survey, clinical (spleen enlargement, axillary temperature, weight) and parasitological data (malaria parasite densities and species) were collected, as well as blood samples. One hundred and sixty six SNPs were genotyped and 5 immunoassays (AMA1, CSP, MSP1, MSP2, total IgE) were performed on the DNA and serum samples respectively. The data confirm the reduced malaria susceptibility in the Fulani, with a higher level of the protective O-blood group, and increased circulating antibody levels to several malaria antigens (p<10(-15)). We identified SNP allele frequency differences between the 2 ethnic groups in CD36, IL4, RTN3 and ADCY9. Moreover, polymorphisms in FCER1A, RAD50, TNF, SLC22A4, and IL13 genes were correlated with antibody production (p-value<0.003). Further work is required to understand the mechanisms underpinning these genetic factors.

The importance of accuracy in diagnosis of positive malaria cases in a country progressing towards malaria elimination.

BACKGROUND: With Sri Lanka aiming towards malaria elimination by 2015, the National Anti Malaria Campaign has stressed on the importance of identification of the species of Plasmodium either by examination of stained blood smears for malaria parasites or by Rapid Diagnostic Tests for malaria antigens before the initiation of treatment. This study aims at confirmation of the accuracy of clinical and/or microscopical malaria diagnosis using serology. MATERIALS AND METHODS: Study population comprised 51 individuals diagnosed with malaria either microscopically or clinically during the first half of 2011. ELISA for detection of the two significant blood antigens (AMA-1 and MSP1-19) was carried out in these individuals, 14-28 days after being diagnosed as being positive for malaria microscopically. RESULTS: ELISA confirmed the microscopic diagnosis in all 47 of the patients including two mixed infections which flagged positive for both parasite antigens. However, four individuals diagnosed clinically as being positive for P. vivax by Health Care Providers were negative for malaria antibodies by ELISA. CONCLUSIONS: With 175 cases of malaria reported in 2011, a formidable challenge exists to diagnose malaria positive blood smears due to the large number of negative blood smears being seen daily. After routine cross checking of positive slides, it is heartening to note that there were no false positives detected through serological assays amongst patients who were diagnosed as malaria positive by microscopy. Presumptive treatment of febrile patients with anti-malarials can lead to waste of resources and adversely impact the condition of the patient if the fever is not due to malaria.