Search

Summary Objective The development of a biomarker of exposure based on the evaluation of the human antibody response specific to Anopheles salivary proteins seems promising in improving malaria control. The IgG response specific to the gSG6-P1 peptide has already been validated as a biomarker of An. gambiae exposure. This study represents a first attempt to validate the gSG6-P1 peptide as an epidemiological tool evaluating exposure to An. funestus bites, the second main malaria vector in sub-Saharan Africa. Methods A multi-disciplinary survey was performed in a Senegalese village where An. funestus represents the principal anopheline species. The IgG antibody level specific to gSG6-P1 was evaluated and compared in the same children before, at the peak and after the rainy season. Results Two-thirds of the children developed a specific IgG response to gSG6-P1 during the study period and – more interestingly – before the rainy season, when An. funestus was the only anopheline species reported. The specific IgG response increased during the An. funestus exposure season, and a positive association between the IgG level and the level of exposure to An. funestus bites was observed. Conclusions The results suggest that the evaluation of the IgG response specific to gSG6-P1 in children could also represent a biomarker of exposure to An. funestus bites. The availability of such a biomarker evaluating the exposure to both main Plasmodium falciparum vectors in Africa could be particularly relevant as a direct criterion for the evaluation of the efficacy of vector control strategies. Premiere tentative de validation du peptide salivaire gSG6-P1 comme un outil immuno-epidemiologique d’evaluation de l’exposition humaine aux piqures de An. funestus Objectif: Valider le peptide gSG6-P1 comme un outil epidemiologique evaluant l’exposition aux piqures de An. funestus, le second principal vecteur de la malaria en Afrique subsaharienne. Methodes: Etude multidisciplinaire dans un village senegalais ouAn. funestus est la principale espece d’anophele. Le taux d’anticorps IgG specifiques a gSG6-P1 a eteevalue et compare chez les memes enfants avant, durant le pic et a la fin de la saison des pluies. Resultats: Deux tiers des enfants ont developpe une reponse IgG specifique a gSG6-P1 durant la periode etudiee et - plus interessant - avant la saison des pluies, quand An. funestus etait la seule espece d’anophele signalee. La reponse IgG specifique augmentait au cours de saison d’exposition a l’An. funestus et une association positive entre le taux d’IgG et le niveau d’exposition aux piqures de An. funestus a ete observee. Conclusions: Les resultats suggerent que l’evaluation de la reponse IgG specifique a gSG6-P1 chez les enfants pourrait egalement representer un biomarqueur de l’exposition aux piqures de An. funestus. La disponibilite d’un tel biomarqueurs evaluant l’exposition aux deux principaux vecteurs de P. falciparum en Afrique pourrait etre particulierement pertinente en tant que critere pour l’evaluation directe de l’efficacite des strategies de lutte antivectorielle. Primer ensayo para validar el peptido salivar gSG6-P1 como herramienta inmuno-epidemiologica que evalue la exposicion humana frente a picaduras de An. funestus Objetivo: Validar el peptido gSG6-P1 como herramienta epidemiologica que evalue la exposicion a picaduras de An. funestus, el segundo vector de malaria mas importante en Africa sub-Sahariana. Metodos: Estudio multidisciplinar, en un poblado senegales en donde An. funestus es la principal especie anofelina. Los niveles de anticuerpos IgG especificos para gSG6-P1 se evaluaron y compararon en los mismos ninos antes, durante el pico y despues de la estacion de lluvias. Resultados: Dos tercios de los ninos desarrollaron una IgG especifica para gSG6-P1 durante el periodo de estudio y – mas interesante aun – antes de la epoca lluviosa, cuando An. funestus era la unica especie anofelina reportada. La respuesta IgG especifica aumento durante el periodo de exposicion a An. funestus y se observo una asociacion positiva entre el nivel de IgG y el nivel de exposicion a picaduras de An. funestus. Conclusiones: Los resultados sugieren que la evaluacion de la respuesta IgG especifica para gSG6-P1 en ninos tambien podria utilizarse como un biomarcador de exposicion a picaduras de An. funestus. La disponibilidad de un biomarcador que evalua la exposicion a los dos principales vectores de P. falciparum en Africa podria ser particularmente relevante como un criterio directo para la evaluacion de la eficacia de estrategias de control vectorial.

The upsurge of diarrhoea observed in children in Kosovo Mitrovica in the spring of 2001 led to a survey, jointly organized by the city health department, the GISPE association and the medical laboratory at the Val de Grâce Hospital (France). The available retrospective data showed an increase in cases of diarrhoea in which Giardia duodenalis was isolated. During the third week of August 2001, all children with diarrhoea consulting in the hospital south of city (n = 45) had a complete stool analysis. The analyses showed the presence of Giardia cysts and trophozoites in 40% of the cases, and no cases with helminthes or cryptosporidia. Moreover 3 strains of S. sonnei, a microorganism never previously identified, and different pathovars of E. coli in 11 patients were isolated. This "epidemic" appeared to be linked to the poor hygiene conditions that still prevailed 2 years after the events but not directly to the water supply, which was rehabilitated at the end of 1999. It is also necessary to strengthen the capacity of the public laboratories and health-care facilities of the province.

The reduction of Schistosoma fecundity observed after experimental vaccination with the Schistosoma mansoni 28-kDa glutathione S-transferase (Sm28GST) antigen has been related to the inhibition of glutathione S-transferase (GST) enzymatic activity by specific antibody. The humoral immune response to the protective antigen Sm28GST and to the epitopes involved in the enzymatic site (amino acid [aa] sequences 10-43 and 190-211) was evaluated in infected individuals before chemotherapy treatment. The capacity of the serum samples to inhibit GST enzymatic activity was assessed. Specific IgG3 response was predominant in the male population with a low intensity of infection and was associated with maximal GST inhibition. In contrast, the neutralizing activity of serum samples from women with a low intensity of infection was correlated with high specific IgA response specifically directed toward the 190-211 epitope. These results strongly support the hypothesis that GST-neutralizing IgG3 and IgA isotypes are sex dependent. The relationship of this specific acquired immune response with the level of intensity of infection is discussed.

A recently reported epidemic of Schistosoma mansoni infection in Senegal provided an opportunity to study the dynamics of the development of immunity to human schistosomiasis. We report here on the cell-mediated immune response in a population of 99 females and 95 males, with particular emphasis on the relationship between intensity of infection and age. We found that the intensity of infection correlated negatively with age in females but not in males. In men and women, both Th1- and Th2-type cytokines were detected upon in vitro stimulation of PBMCs with soluble egg antigen (SEA) or soluble adult worm antigens (SWAP). In the female group, SEA-induced PBMC proliferation was associated with the production of IFN-gamma, IL-2 and IL-5, all of which correlated negatively with intensity of infection. Most cytokine production correlated positively with age. Spontaneous production of TNF-alpha, IL-6 and IL-10 was higher in the infected population than in an uninfected control group. Our results suggest that immunity to infection could be more pronounced in the female population and associated with a Th0/1 + 2 pattern of cytokine secretion mediated by soluble egg antigen (SEA).

a b s t r a c t Malaria immunity is modulated by many environmental and epidemiological factors. This study evaluates the influence of a hitherto unstudied environmental-epidemiological fac- tor, namely the impact of human exposure to Anopheles bites on the isotype profile of acquired antibody responses to Plasmodium falciparum. In two Senegalese villages where the intensity of exposure to Anopheles bites was markedly different (high and low exposure), specific IgG1 and IgG3 responses to P. falciparum whole schizont extract (WSE) and circum- sporozoite protein (CSP) were evaluated at the peak of Anopheles exposure (September) and later (December) in a cohort of 120 children aged 3-8 years. Multivariate analysis showed a significantly lower IgG1 response against P. falciparum WSE and CSP in children highly exposed to Anopheles bites (Gankette) compared to those who were weakly exposed (Mboula). In contrast, in both villages, parasitemia and increasing age were strongly asso- ciated with higher IgG1 and IgG3 levels. We hypothesize that high exposure to Anopheles bites could inhibit IgG1-dependent responsiveness to P. falciparum known to induce protec- tive immune responses against malaria. The impact of mosquito saliva on the regulation of specific protective immunity may need to be taken into account in epidemiological studies and trials for malaria vaccines.

Background The evaluation of malaria transmission intensity is a crucial indicator for estimating the burden of malarial disease. In this respect, entomological and parasitological methods present limitations, especially in low transmission areas. The present study used a sensitive multiplex assay to assess the exposure to Plasmodium falciparum infection in children living in an area of low endemicity. In three Senegalese villages, specific antibody (IgG) responses to 13 pre-erythrocytic P. falciparum peptides derived from Lsa1, Lsa3, Glurp, Salsa, Trap, Starp, Csp and Pf11.1 proteins were simultaneously evaluated before (June), at the peak (September) and after (December) the period of malaria transmission, in children aged from 1 to 8 years. Results Compared to other antigens, a high percentage of seropositivity and specific antibody levels were detected with Glurp, Salsa1, Lsa3NR2, and Lsa1J antigens. The seropositivity increased with age for all tested antigens. Specific IgG levels to Glurp, Salsa1, Lsa3NR2, and Lsa1J were significantly higher in P. falciparum infected children compared to non-infected and this increase is significantly correlated with parasite density. Conclusion The multiplex assay represents a useful technology for a serological assessment of rapid variations in malaria transmission intensity, especially in a context of low parasite rates. The use of such combined serological markers (i.e. Glurp, Lsa1, Lsa3, and Salsa) could offer the opportunity to examine these variations over time, and to evaluate the efficacy of integrated malaria control strategies.

Although domestic animals may not be permissive for Plasmodium, they could nevertheless play a role in the epidemiology of malaria by attracting Anopheles away from humans. To investigate interactions between domestic animals and mosquitoes, we assayed immunoglobulin G (IgG) antibodies directed against the salivary proteins of Anopheles gambiae in domestic animals living in Senegalese villages where malaria is endemic. By Western blotting, sera from bovines (n = 6), ovines (n = 36), and caprines (n = 36) did not react with Anopheles whole saliva. In contrast, equine sera recognized proteins in both saliva and salivary gland extracts. Two of the major immunogens (32 and 72 kDa) were also reactive in extracts from other major mosquito genera (Aedes and Culex), but reactions to Anopheles-specific antigens were detected in 12 of 17 horses. These data suggest that horses strongly react to Anopheles bites, and further experiments on horses are warranted to investigate the impact of this domestic animal species on the transmission of human malaria.

The upsurge of diarrhoea observed in children in Kosovo Mitrovica in the spring of 2001 led to a survey, jointly organized by the city health department, the GISPE association and the medical laboratory at the Val de Grâce Hospital (France). The available retrospective data showed an increase in cases of diarrhoea in which Giardia duodenalis was isolated. During the third week of August 2001, all children with diarrhoea consulting in the hospital south of city (n = 45) had a complete stool analysis. The analyses showed the presence of Giardia cysts and trophozoites in 40% of the cases, and no cases with helminthes or cryptosporidia. Moreover 3 strains of S. sonnei, a microorganism never previously identified, and different pathovars of E. coli in 11 patients were isolated. This "epidemic" appeared to be linked to the poor hygiene conditions that still prevailed 2 years after the events but not directly to the water supply, which was rehabilitated at the end of 1999. It is also necessary to strengthen the capacity of the public laboratories and health-care facilities of the province.

Following the implementation of two dams in the Senegal River, entomological and parasitological studies were conducted in three different ecological zones in the Senegal River Basin (the low valley of Senegal River, the Guiers Lake area and the low valley of Ferlo) every 3 month in June 2004, September 2004, December 2004 and March 2005. The objective of this work was to study the influence of environmental heterogeneities on vector bionomics and malaria epidemiology. Mosquitoes were collected when landing on human volunteers and by pyrethrum spray catches. In the parasitological survey, blood samples were taken from a cohort of schoolchildren under 9 years during each entomology survey. Seven anopheline species were collected: Anopheles arabiensis, Anopheles gambiae M form, Anopheles funestus, Anopheles pharoensis, Anopheles coustani, Anopheles wellcomei and Anopheles rufipes. A. arabiensis, A. funestus and A. pharoensis were predominant in the low valley of the Senegal River, A. funestus in the Guiers Lake area and A. arabiensis in the low valley of Ferlo. Mosquito populations' dynamics varied temporally depending on the rainy season for each zone. The anthropophilic rates varied between 6 and 76% for A. gambiae s.l. and 23 and 80% for A. funestus. Only 4/396 A. pharoensis and 1/3076 A. funestus tested carried Plasmodium falciparum CS antigen. These results suggest the implication of A. pharoensis in malaria transmission. The related entomological inoculation rates were estimated to 10.44 in Mbilor and 3 infected bites in Gankette Balla and were due, respectively, to A. pharoensis and A. funestus. Overall, 1636 thick blood smears were tested from blood samples taken from schoolchildren with, respectively, a parasite and gametocyte average prevalence of 9 and 0.9%. The parasite prevalence was uniformly low in Mbilor and Gankette Balla whereas; it increased in September (16%) and then remained stable in December and March (22%) in Mboula where malaria transmission was not perceptible. However, significant differences were observed over time for parasite prevalence in Mbilor and Mboula villages whereas; it was only in Gankette Balla village where gametocyte prevalence was significantly different over time. Our study demonstrates the influence of ecological changes resulted from dams implementation in the Senegal River on the composition of vectorial system, malaria transmission and epidemiology. Such changes should be thoroughly surveyed in order to prevent any possible malaria outbreak in the Senegal River Basin.

A study was carried out in France in collaboration with the meat industry to investigate the occurrence and characteristics of Shiga toxin-producing E. coli (STEC) and O157 E. coli in a population of healthy bovines representative of French livestock. A total of 851 animals belonging to three bovine classes (106 young bulls, 374 dairy cows and 371 meat cows) were included in the study. Samples of feces and of the corresponding carcasses were collected from March 97 to August 97 in seven abattoirs spread throughout the national territory. STEC cultures from the 1702 samples were screened using PCR for the presence of stx genes. Positive samples were further subjected to colony blot hybridization and to O157-specific immunomagnetic separation. Probe-positive colonies and O157 colonies were then analyzed for the presence of virulence genes and phenotypic characters (serotype, Stx production). In 154 (18.1%) feces and 91 (10.7%) carcass samples stx genes were detected. Two hundred and twenty-two STEC colonies were isolated from 67 (7.9%) feces and 16 (1.9%) carcass samples, with 183 STEC isolated from feces and 39 from carcasses. Only eight O157 isolates were collected from feces samples. None of these O157 E. coli isolates presented stx genes and thus could not be considered as pathogenic regarding hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS). In 3.2% of STEC isolated from feces and in 10.2% of STEC from carcasses eae genes were detected. In 17% of STEC from feces and in 30.7% from carcasses ehx genes were detected. Using these data, the 222 STEC colonies could be classified in 11 different 'virulence patterns' (presence/absence of stx1, stx2, eae and ehx genes), showing that more than 77% of isolates presented only one virulence factor. Only three STEC on 222 colonies (1.3%) presented the three virulence factors stx, eae and ehx in association, none of them reacting with antisera specific for enterohemorrhagic E. coli. (EHEC). These data, together with the fact that only five isolates on the 222 (2.2%) reacted with such antisera (three O111 and two O26 isolates) demonstrated that the natural bacterial populations isolated during this study were clearly distinct from EHEC.