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Abstract Background Malaria remains an important public health problem, particularly in sub-Saharan Africa. In Rwanda, where malaria ranks among the leading causes of mortality and morbidity, disease transmission is influenced by climatic factors. However, there is a paucity of studies investigating the link between climate change and malaria dynamics, which hinders the development of effective national malaria response strategies. Addressing this critical gap, this study analyses how climatic factors influence malaria transmission across Rwanda, thereby informing tailored interventions and enhancing disease management frameworks. Methods The study analysed the potential impact of temperature and cumulative rainfall on malaria incidence in Rwanda from 2012 to 2021 using meteorological data from the Rwanda Meteorological Agency and malaria case records from the Rwanda Health Management and Information System. The analysis was performed in two stages. First, district-specific generalized linear models with a quasi-Poisson distribution were applied, which were enhanced by distributed lag non-linear models to explore non-linear and lagged effects. Second, random effects multivariate meta-analysis was employed to pool the estimates and to refine them through best linear unbiased predictions. Results A 1-month lag with specific temperature and rainfall thresholds influenced malaria incidence across Rwanda. Average temperature of 18.5 °C was associated with higher malaria risk, while temperature above 23.9 °C reduced the risk. Rainfall demonstrated a dual effect on malaria risk: conditions of low (below 73 mm per month) and high (above 223 mm per month) precipitation correlated with lower risk, while moderate rainfall (87 to 223 mm per month) correlated with higher risk. Seasonal patterns showed increased malaria risk during the major rainy season, while the short dry season presented lower risk. Conclusion The study underscores the influence of temperature and rainfall on malaria transmission in Rwanda and calls for tailored interventions that are specific to location and season. The findings are crucial for informing policy that enhance preparedness and contribute to malaria elimination efforts. Future research should explore additional ecological and socioeconomic factors and their differential contribution to malaria transmission. more...

Background: High parasite-specific antibody levels are generally associated with low susceptibility to Plasmodium falciparum malaria. This has been supported by several studies in which clinical malaria cases of P. falciparum malaria were reported to be associated with low antibody avidities. This study was conducted to evaluate the role of age, malaria transmission intensity and incidence of clinical malaria in the induction of protective humoral immune response against P. falciparum malaria in children living in Burkina Faso., Methods: We combined levels of IgG and IgG subclasses responses to P. falciparum antigens: Merozoite Surface Protein 3 (MSP3), Merozoite Surface Protein 2a (MSP2a), Merozoite Surface Protein 2b (MSP2b), Glutamate Rich Protein R0 (GLURP R0) and Glutamate Rich Protein R2 (GLURP R2) in plasma samples from 325 children under five (05) years with age, malaria transmission season and malaria incidence., Results: We notice higher prevalence of P. falciparum infection in low transmission season compared to high malaria transmission season. While, parasite density was lower in low transmission than high transmission season. IgG against all antigens investigated increased with age. High levels of IgG and IgG subclasses to all tested antigens except for GLURP R2 were associated with the intensity of malaria transmission. IgG to MSP3, MSP2b, GLURP R2 and GLURP R0 were associated with low incidence of malaria. All IgG subclasses were associated with low incidence of P. falciparum malaria, but these associations were stronger for cytophilic IgGs., Conclusions: On the basis of the data presented in this study, we conclude that the induction of humoral immune response to tested malaria antigens is related to age, transmission season level and incidence of clinical malaria. more...

In the present study, the influences of FcγRIIA polymorphism on susceptibility to malaria and antibody responses to Plasmodium falciparum antigens were analyzed in children. We recruited 96 healthy children between 3 and 10 years at the beginning of the high transmission season and we followed up for 5 months through the high transmission season to assess the parasitological, immunological and genetic endpoints in relation to clinical malaria status. There was a similar distribution of homozygous and heterozygous individuals carrying the FcγRIIA-131R/R and FcγRIIA-131R/H allele, whereas the number of FcγRIIA-131H/H homozygous individuals was lower. P. falciparum infection frequency was not associated with the FcγRIIa-131R/H polymorphism. Only IgG antibody responses to GLURP R0 showed a significant association between antibody levels and FcγRIIA polymorphism (p=0.02). IgG levels to MSP2a were significantly higher in children who did not experience any clinical malaria episode compared to those who experienced at least one malaria episode (p=0.019). Cytophilic and non-cytophylic IgG subclass levels were higher in children without malaria than those who experienced at least one malaria episode. This difference was statistically significant for IgG1 to MSP3 (p=0.003) and to MSP2a (p=0.006); IgG3 to MSP2a (p=0.007) and to GLURP R0 (p=0.044); IgG2 to MSP2b (p=0.007) and IgG4 to MSP3 (p=0.051) and to MSP2a (p=0.049). In this study, homozygous carriers of the FcγRIIA-131R/R allele had higher malaria-specific antibody levels compare to the heterozygous carriers FcγRIIA-131R/H alleles and to homozygous carriers of FcγRIIA-131H/H alleles. The pre-existing antibodies responses were related to a reduced subsequent risk of clinical malaria., (Copyright © 2014 Elsevier B.V. All rights reserved.) more...

Background: Over the past ten years, Rapid Diagnostic Tests (RDT) played a major role in improving the use of biological malaria diagnosis, in particular in poor-resources settings. In Burkina Faso, a recent Demography and Health Survey (DHS) gave the opportunity to assess the performance of the Paracheck® test in under five children nationwide at community level., Methods: A national representative sample of 14,947 households was selected using a stratified two-stage cluster sampling. In one out of two households, all under five children were eligible to be tested for malaria using both RDT and microscopy diagnosis. Paracheck® performance was assessed using miscroscopy as the gold standard. Sensitivity and specificity were calculated as well as the diagnosis accuracy (DA) and the Youden index., Results: The malaria infection prevalence was estimated at 66% (95% CI: 64.8-67.2) according to microscopy and at 76.2% (95% CI: 75.1-77.3) according to Paracheck®. The sensitivity and specificity were estimated at 89.9% (95% CI: 89.0-90.8) and 50.4% (95% CI: 48.3-52.6) respectively with a Diagnosis Accuracy of 77% and a Youden index of 40%. The positive predictive value for malaria infection was 77.9% (95% CI: 76.7-79.1) and the negative predictive value was 72.1% (95% CI: 69.7-74.3). Variations were found by age group, period of the year and urban and rural areas, as well as across the 13 regions of the country., Conclusion: While the sensitivity of the Paracheck® test was high, its specificity was poor in the general under five population of Burkina Faso. These results suggest that Paracheck® is not suitable to assess malaria infection prevalence at community level in areas with high malaria transmission. In such settings, malaria prevalence in the general population could be estimated using microscopy. more...

FcγRIIa is known to be polymorphic; and certain variants are associated with different susceptibilities to malaria. Studies involving the Fulani ethnic group reported an ethnic difference in FcγRIIa-R131H genotype frequencies between the Fulani and other sympatric groups. No previous studies have addressed these questions in Burkina Faso. This study aimed to assess the influence of FcγRIIa-R131H polymorphism on anti-falciparum malaria IgG and IgG subclass responses in the Fulani and the Mossi ethnic groups living in Burkina Faso. Healthy adults more than 20 years old belonging to the Mossi or the Fulani ethnic groups were enrolled for the assessment of selected parasitological, immunological and genetic variables in relation to their susceptibility to malaria. The prevalence of the Plasmodium falciparum infection frequency was relatively low in the Fulani ethnic group compared to the Mossi ethnic group. For all tested antigens, the Fulani had higher antibody levels than the Mossi group. In both ethnic groups, a similar distribution of FcγRIIa R131H polymorphism was found. Individuals with the R allele of FcγRIIa had higher antibody levels than those with the H allele. This study confirmed that malaria infection affected less the Fulani group than the Mossi group. FcγRIIa-R131H allele distribution is similar in both ethnic groups, and higher antibody levels are associated with the FcγRIIa R allele compared to the H allele., (© 2012 The Authors. Scandinavian Journal of Immunology © 2012 Blackwell Publishing Ltd.) more...

One approach to investigate if human genetic variation influences the selection of Plasmodium falciparum drug resistance is to compare the frequency of resistant infections among human populations differing in their genetic background and living in the same epidemiological context. A further complementary approach consists in comparing drug resistance among subjects differing for genes involved in drug metabolism. Here we report, from malariological surveys performed in Burkina Faso, that the prevalence of P. falciparum chloroquine-resistant infections (pfcrt 76T and/or pfmdr1 86Y alleles) differs among sympatric ethnic groups, being higher in the Mossi and Rimaibé groups than in the Fulani group (odds ratio [OR], 2.24; 95% confidence interval [CI], 1.27-3.92; P = .007). The association analysis revealed that the human CYP2C8*2 variant, known to determine a poor drug metabolizer phenotype, was associated with P. falciparum chloroquine-resistant infections (OR, 1.66; 95% CI, 1.13-2.43; P = .008). This variant is more frequent in the Mossi-Rimaibé group (23.7% ± 1.4%) than in the Fulani group (9.9% ± 2.5%; P = .0003). This study provides an example of how host genetic variation may influence the selection dynamics of a pathogen's drug resistance. more...

In order to prevent the destruction of the ecology and to sustain the flora mainly for medicinal plants, we investigated on alternative parts taken from four plants already known to display antiplasmodial activities and largely used by traditional healers in sub-Saharan Africa. The evaluated parts are bark of trunk for Zanthoxylum zanthoxyloides and leaves for Sarcocephalus latifolius instead of roots, and leaves for Combretum molle and Anogeissus leiocarpus instead of stem bark. The antiplasmodial activity of extracts of these plants was evaluated in vitro using the multi-resistant strain (W2) of Plasmodium falciparum. Antiproliferative activity was also assessed, using K562S human monocyte cell lines, along with calculation of the selectivity index (SI) of each extract. The highest in vitro antiplasmodial activity was found in the alkaloid extract of trunk bark from Z. zanthoxyloides and from the MeOH extract of A. leiocarpus leaves (IC(50) = 1.2 microg/mL and 4.9 microg/mL, respectively) with good selectivity index. Moderate activity was found in the MeOH extract (IC(50) = 5.7 microg/mL) and MeOH/H2O extract (IC(50) = 7.9 microg/mL) of C. molle leaves. Moderate activity was also found in the MeOH/H20 extract (IC(50) = 5.2 microg/mL) and the decoction (IC(50) = 8.2 microg/mL) from leaves of A. leiocarpus. No good activity was found with extracts from roots of S. latifolius. All extracts tested displayed low levels of cytotoxicity against K562S cells. The data generated clearly show that the trunk bark for Z. zanthoxyloides and the leaves for A. leiocarpus and C. molle could be used for the treatment of malaria instead of roots and stem bark. more...

The impact of vector control measures on the evolution of antimalarial drug resistance is an important issue for malaria control programs. We investigated whether the in vivo efficacy of chloroquine (CQ) in children aged 6-59 months with uncomplicated malaria differed in 9 villages that had benefited from long-term use of insecticide-treated curtains (ITCs) and in 9 nearby non-ITC villages. We also compared the prevalence of genetic markers of resistance to CQ and sulfadoxine-pyrimethamine (SP) between the two groups of villages. The study enrolled 1,035 children with uncomplicated malaria and 231 infected but asymptomatic children. After taking account of re-infections, the proportions of children who experienced clinical failure after treatment with CQ were 14% and 19% in ITC and non-ITC villages, respectively (OR = 0.68; 95% CI: 0.39, 1.18). Parasitologic failure was observed in 49% of children in ITC villages and 58% of children in non-ITC villages (OR = 0.71 95%CI: 0.44, 1.13). The proportion of symptomatic children who harbored parasites carrying the pfcrt-76T allele was 43% in ITC villages and 40% in non-ITC villages (OR = 1.09; 95%CI: 0.80, 1.50). The pfmdr1-86Y allele was detected in 31% and 29% of children in the two groups of villages (OR = 1.14; 95%CI: 0.75, 1.72). Triple mutations in the dhfr gene were observed in 12% of children in both groups. No double mutations in the dhps gene were observed. Similar results were observed in asymptomatic children. In this setting, ITC use was not associated with increased circulation of parasites resistant to standard antimalarial drugs, or with a greater risk of treatment failure among children less than 5 years of age. more...

The well-established relative resistance to malaria observed in the Fulani as compared with other sympatric tribes in West Africa has been attributed to their higher levels of serum immunoglobulin (Ig) G antibodies to malarial antigens. In this study, we confirm and extend the previous findings by analyses of the levels of IgM, IgG and IgG subclasses of anti-malarial antibodies in asymptomatic individuals of different sympatric tribes in Burkina Faso (Fulani/Mossi) and Mali (Fulani/Dogon). The Fulani showed significantly higher median concentrations of anti-malarial IgG and IgM antibodies than the sympatric tribes at both locations. Although the overall subclass pattern of antibodies did not differ between the tribes, with IgG1 and IgG3 as dominant, the Fulani showed consistently significantly higher levels of these subclasses as compared with those of the non-Fulani individuals. No significant differences were seen in the levels of total IgG between the tribes, but the Fulani showed significantly higher levels of total IgM than their neighbours in both countries. While the antibody levels to some nonmalarial antigens showed the same pattern of differences seen for antibody levels to malaria antigens, no significant such differences were seen with antibodies to other nonmalarial antigens. In conclusion, our results show that the Fulani in two different countries show higher levels of anti-malarial antibodies than sympatric tribes, and this appears not to be a reflection of a general hyper-reactivity in the Fulani. more...

A longitudinal study was undertaken in Burkina Faso among 293 children aged 6 months to 9 years in order to determine the correlation between an antibody response to several individual malarial antigens and malarial infection. It was found that the presence of a positive antibody response at the beginning of the rainy season to three long synthetic peptides corresponding to Plasmodium falciparum Exp-1 101-162, MSP-3 154-249 and GLURP 801-920 but not to CSP 274-375 correlated with a statistically significant decrease in malarial infection during the ongoing transmission season. The simultaneous presence of an antibody response to more than one antigen is indicative of a lower frequency of malarial infection. This gives scientific credibility to the notion that a successful malaria vaccine should contain multiple antigens. more...

In Burkina Faso, where malaria is hyper-endemic and transmission intensity is very high, the majority of malaria-related morbidity and mortality occurs in children less than 5 years of age. A control measure such as the use of insecticide-treated curtains (ITC) significantly reduces transmission of malaria infection. Concerns remain whether reduced transmission intensity may lead to a delay in the development of immunity in younger children and even to a partial loss of already acquired immunity. In this study, the levels of P. falciparum-specific IgG subclasses, the number of infecting parasite clones determined by PCR-based genotyping of the msp2 gene and the parasite density were analysed in 154 asymptomatic children (3-6 years) living in 16 villages (8 with and 8 without ITC) in the vicinity of Ouagadougou, the capital of Burkina Faso. In addition, the parasite inhibitory effects of Ig fractions, prepared from selected children, in co-operation with normal human monocytes were studied. Blood samples from asymptomatic ITC-users showed a significant decrease in P. falciparum prevalence as well as in parasite density. However, no significant difference was observed in P. falciparum-specific antibodies or in parasite multiplicity of infection between the two groups. Furthermore, Ig fractions from children of both groups showed similar levels of inhibitory activity against autologous parasite growth both on their own and in co-operation with monocytes. more...

Objectives: To determine the impact of insecticide-treated curtains (ITC) on all-cause child mortality (6-59 months) over a period of six years. To determine whether initial reductions in child mortality following the implementation of ITC are sustained over the longer term or whether "delayed" mortality occurs., Methods: A rural population of ca 100 000 living in an area with high, seasonal Plasmodium falciparum transmission was studied in Burkina Faso. Annual censuses were conducted from 1993 to 2000 to measure child mortality. ITC to cover doors, windows, and eaves were provided to half the population in 1994 with the remainder receiving ITC in 1996. Curtains were re-treated or, if necessary, replaced annually., Findings: Over six years of implementation of ITC, no evidence of the shift in child mortality from younger to older children was observed. Estimates of the reduction in child mortality associated with ITC ranged from 19% to 24%., Conclusions: In our population there was no evidence to suggest that initial reduction in child mortality associated with the introduction of insecticide-treated materials was subsequently compromised by a shift in child mortality to older-aged children. Estimates of the impact of ITC on child mortality in this population range from 19% to 24%. more...

Antibody-mediated inhibition of Plasmodium falciparum parasites in vitro reflects the potential parasite-neutralizing activity of the antibodies in vivo. In this study, immunoglobulins and P. falciparum isolates were collected from children with asymptomatic malaria in Burkina Faso. We demonstrate a significantly lower in vitro growth inhibitory activity against the P. falciparum field isolates by autologous host immunoglobulin compared with that of immunoglobulin from other individuals. To gain further insight to possible mechanisms for the diverse sensitivity observed, analyses of consecutive isolates taken 14 days apart were performed with regard to polymerase chain reaction-based genotyping and sensitivity to growth inhibition in vitro. All the asymptomatic infections were composed of multiple, genotypically distinct parasite clones, and at least one new parasite clone appeared in most of the day 14 isolates compared with the corresponding day 0 isolates. Apparently persisting parasite clones, present in both the day 0 and day 14 isolates from the same person, were also frequently observed. The day 14 isolates were more effectively inhibited by autologous day 14 immunoglobulin than by the corresponding day 0 immunoglobulin in 57% of the cases. However, the frequent presence of persisting parasite clones in asymptomatic children indicates that the parasite may develop a relative resistance to neutralizing immune responses. more...

The present work describes the recognition of three synthetic polypeptides encompassing the N- and C-terminal regions of the transmembrane Exp-1 protein of the parasite Plasmodium falciparum by plasma and peripheral blood mononuclear cells from naturally exposed individuals living in African endemic areas. The three polypeptides comprise the sequences 23-105, 73-162 and 101-162, and overlap at the transmembrane domain (73-105). Thus, they permitted characterization of the immune response specific to the N- and C-terminal domains in an independent fashion. Two different populations were evaluated, one in the village of Safo in Mali and the other in the villages of Somnaway, Kabortenga and Toussouktenga in Burkina Faso. Antibodies to the sequence 73-162 of Pf Exp-1 were found in 70% of adult Mali donors and in all of the donors tested from Burkina Faso. Strikingly, the N-terminal fragment Pf Exp-1 23-105 was only weakly recognized by a few donors. Evaluation of the T-cell response indicated that the peptide Pf Exp-1 23-105 was more potent than Pf Exp-1 73-162 in inducing a proliferative response. A correlation between peptide-specific interferon-gamma and interleukin-6 production and proliferation to peptide Pf Exp-1 23-105 was observed. Further studies are needed to evaluate this molecule as a vaccine candidate. more...

To assess the possible impact of insecticide treated curtains (ITC) on the composition of a Plasmodium falciparum population in a rural area of Burkina Faso, blood samples were collected during the rainy season of 1997 from 226 children aged 3-6 years, from 4 villages equipped with ITC and 2 control villages without ITC. The analysis of fragment lengths of 3 highly polymorphic P. falciparum genes (msp-1, msp-2 and glurp) revealed a maximum number of 3 alleles per infected person for each gene. The mean number of clones per infected person was similar in villages with and without ITC. more...

CD8(+) cytolytic T lymphocytes (CTL) play a fundamental role in the clearance of malaria parasites from the liver in mouse models. In humans, however, only low levels of parasite-specific CD8(+) T lymphocytes have been observed in individuals living in endemic areas. In the present study, we identified high levels of circulating CD8(+) T lymphocytes specific for a previously described HLA-A2-restricted CTL epitope of the circumsporozoite (CS) protein of Plasmodium falciparum in an adult living in Burkina Faso, as evidenced by IFN-gamma ELISPOT assay and MHC-tetramer technology. After cloning by limiting dilution culture, T cell recognition of natural CS variants of P. falciparum was studied. The results demonstrate that naturally occurring variations drastically affect residues critical for T cell recognition as only two out of nine sequences analyzed were efficiently recognized by the CTL clones. These clones were also used to analyze T cell recognition of the endogenously presented cognate antigen. We observed efficient antigen recognition of both HLA-A*0201-transfected murine antigen presenting cells and liver cells from HLA-A*0201/K(b)-transgenic mice upon infection with recombinant vaccinia virus encoding the CS protein (WR-CS). More importantly, we demonstrate for the first time efficient recognition of WR-CS-infected human liver cells. more...

The role of antigen specific CD8+ T-lymphocytes in mediating protection against sporozoite-induced malaria has been well established in murine models. In humans, indirect evidence has accumulated suggesting a similar protective role for antigen-specific CD8+ T-lymphocytes. Nevertheless, the low frequency of circulating specific cells together with the lack of sensitive methods to quantify them has hampered the direct assessment of their function. Using a combination of short-term cell culture and IFN-gamma ELISPOT, we studied CD8+ T-lymphocyte responses to a panel of HLA-A*0201 binding peptides. In addition to confirming the response to already described epitopes, we also identified five new CD8+ T-lymphocyte epitopes. These epitopes are presented in pre-erythrocytic stages gene products of Plasmodium falciparum 7G8 strain and correspond to the following protein segments: circumsporozoite (CS) 64-72, 104-113, 299-308 and 403-411; liver stage antigen (LSA-1) repeat region; sporozoite surface protein 2 or thrombospondin related anonymous protein (SSP2/TRAP) 78-88 and 504-513. Four of these peptides are conserved amongst all published sequences of P. falciparum strains. We conclude that the modified IFN-gamma ELISPOT assay is a sensitive technique to monitor antigen-specific CD8+ T-lymphocyte responses in human malaria which may help in the improvement and assessment of the efficacy of malaria subunit vaccines. more...

The results of the first two years of implementation of a large scale trial of insecticide-treated curtains in Burkina Faso are summarised in this presentation. The trial was conducted in a highly malarious area and involved a population of slightly less than 100,000, distributed in 158 villages over an area of almost 1000 km2. A remarkable impact on entomological parameters (Anopheles density, sporozoite rate, entomological inoculation rate) was accompanied by a relatively modest reduction of parasitological indices (prevalence and density of Plasmodium falciparum). All-cause mortality in children 0.5 to 5 year old showed over two years a 15% decline. The authors believe that the wide surface of the protected zone and the almost total coverage achieved in the intervention villages were the major determinants of the observed reduction of transmission. A conclusive interpretation of the mortality results requires a further follow-up of the study population. more...

A large, randomized controlled trial to investigate the impact of insecticide-treated curtains (ITC) on child mortality was conducted in an area of seasonal, holoendemic malaria in Burkina Faso. 158 communities totalling some 90,000 people were censused and grouped into 16 geographical clusters, 8 of which were randomly selected to receive ITC in June-July 1994, just prior to the rainy season. In September-October 1995, at the peak period of malaria transmission, a cross-sectional survey was conducted in 84 of the villages. A random sample of 905 children aged 6-59 months was identified and visited. 763 children (84%) were present at the time of the visit and recruited into the study. Mothers were asked about fever in the past 24 h, the child's temperature was taken, and a sample of blood collected to identify and quantify malaria infections and to measure haemoglobin (Hb) levels. Children protected by ITC were less likely to be infected with Plasmodium falciparum (risk ratio = 0.92; 95% CI 0.86, 0.98) or P. malariae (risk ratio = 0.42, 95% CI 0.19, 0.95). The mean intensity of P. falciparum infections was lower among children protected by ITC (899 vs. 1583 trophozoites/microliter; P < 0.001), while the mean Hb level was 0.4 g/dl higher (P < 0.001). While we found no evidence that ITC had an impact on the prevalence of malaria-associated fever episodes, the confidence intervals around our estimates of the impact of ITC on malaria morbidity were wide. We conclude that widespread implementation of ITC in this area of high malaria transmission led to a modest reduction in the prevalence of malaria infection and to a more substantial reduction in the intensity of these infections which caused increased Hb levels. We were unable to demonstrate any impact of ITC on malaria morbidity, but the wide confidence intervals around our point estimates do not preclude the possibility of a substantial impact. more...

It has been shown that insecticide-treated bed nets or curtains may reduce morbidity and mortality from malaria in hyper-holoendemic areas of sub-Saharan Africa. This protection could partially depend on the transitory imbalance between the anti-malaria immunity acquired by the population before the intervention and the lowered sporozoite load resulting from the anti-vector measure. To verify if the efficacy of the intervention is influenced by the baseline immune status of the population, we compared the protective effect of permethrin-impregnated curtains (PIC) against malaria infection among groups with different baseline levels of anti-malaria immunity. We analyzed the impact of PIC on the Plasmodium falciparum infection rate in two rural villages of Burkina Faso inhabited by three ethnic groups: the Fulani, Mossi, and Rimaibé. These have been previously shown to differ for several malariologic indices, with the Fulani being characterized by lower infection and disease rates and by higher immune response to P. falciparum with respect to the other ethnic groups. The PIC were distributed in June 1996 and their impact on malaria infection was evaluated in groups whose baseline levels of immunity to malaria differed because of their age and ethnic group. Age- and ethnic-dependent efficacy of the PIC was observed. Among the Mossi and Rimaibé, the impact (parasite rate reduction after PIC installation with respect to the pre-intervention surveys) was 18.8% and 18.5%, respectively. A more than two-fold general impact (42.8%) was recorded in the Fulani. The impact of the intervention on infection rates appears positively correlated with the levels of anti-malaria immunity. Since decreased transmission entails a reduction of immunity, the efficacy of the intervention in the long term cannot be taken for granted. The expected complementary role of a hypothetical vaccine is stressed by these results, which also emphasize the importance of the genetic background of the population in the evaluation and application of malaria control strategies. more...

The comparison of malaria indicators among populations that have different genetic backgrounds and are uniformly exposed to the same parasite strains is one approach to the study of human heterogeneties in the response to the infection. We report the results of comparative surveys on three sympatric West African ethnic groups, Fulani, Mossi, and Rimaibé, living in the same conditions of hyperendemic transmission in a Sudan savanna area northeast of Ouagadougou, Burkina Faso. The Mossi and Rimaibé are Sudanese negroid populations with a long tradition of sedentary farming, while the Fulani are nomadic pastoralists, partly settled and characterized by non-negroid features of possible caucasoid origin. Parasitological, clinical, and immunological investigations showed consistent interethnic differences in Plasmodium falciparum infection rates, malaria morbidity, and prevalence and levels of antibodies to various P. falciparum antigens. The data point to a remarkably similar response to malaria in the Mossi and Rimaibé, while the Fulani are clearly less parasitized, less affected by the disease, and more responsive to all antigens tested. No difference in the use of malaria protective measures was demonstrated that could account for these findings, and sociocultural or environmental factors do not seem to be involved. Known genetic factors of resistance to malaria did not show higher frequencies in the Fulani. The differences in the immune response were not explained by the entomological observations, which indicated substantially uniform exposure to infective bites. The available data support the existence of unknown genetic factors, possibly related to humoral immune responses, determining interethnic differences in the susceptibility to malaria. more...

Plasmodium falciparum parasite rate, parasite density and anti-CS antibodies were assessed in 196 subjects (age > 10 yrs) belonging to three sympatric West African ethnic groups, namely Mossi, Rimaibé and Fulani, all exposed to very high seasonal malaria transmission in the same rural village near Ouagadougou, Burkina Faso. No interethnic differences were noted in the use of antimalaria measures nor in the exposure to malaria vectors. However, interethnic differences were found in each of the three malariological indices. The Fulani appeared markedly less parasitized and more responsive to the CS-antigen than the Mossi and the Rimaibé who had very similar indices, except in the case of parasite density. These findings suggest a higher resistance to malaria of the Fulani ethnic group, possibly involving human genetic factors and/or the influence of extrinsic variables (e.g., socio-cultural) among which diet differences should be considered. more...

Plasmodium falciparum susceptibility to chloroquine in vivo and to chloroquine, mefloquine, quinine, amodiaquine and sulfadoxine/pyrimethamine in vitro was investigated in children living in Goundry village, Oubritenga Province (Burkina Faso) in November 1992. An extended WHO in vivo field test was used, with follow-up on days 2, 4, 7, 14, 21 and 28 after treatment with 25 mg chloroquine per kg body weight given over 3 days, in children from 2 to 8 years old with P. falciparum monospecific infection, asexual parasitaemia > 800 parasites/microliter of blood and negative Bergqvist urine tests. At the same time, the in vitro response was assessed using WHO standard test kits. Out of the 71 in vivo responses examined, 50 (70.4%) were classified as resistant to chloroquine at RI (43.6%) or RII (26.8%) levels. There were no RIII responses. Out of the 43 isolates tested for chloroquine susceptibility in vitro, 32 (74.4%) were resistant to the drug with mean EC50 and EC99 values of 1.41 mumol and 10.96 mumol/l of blood, respectively. Resistance to sulfadoxine/pyrimethamine in vitro was observed in one out of 19 tested cases, with mean EC50 and EC99 values of 0.00002 mumol and 35.05 mumol/l of blood, respectively. All isolates were inhibited by mefloquine at 12.8 mumol/l of blood, quinine at 51.2 mumol/l of blood and amodiaquine at 0.4 mumol/l of blood, indicating full sensitivity to these 3 drugs. The present study demonstrates the high prevalence of chloroquine-resistant strains of P. falciparum in the study area of Burkina Faso and indicates that isolates resistant to sulfadoxine/pyrimethamine may also be present. more...