Dataset Information

Plasmodium falciparum infection during dry season: IgG responses to Anopheles gambiae salivary gSG6-P1 peptide as sensitive biomarker for malaria risk in Northern Senegal.

ABSTRACT: The Northern part of Senegal is characterized by a low and seasonal transmission of malaria. However, some Plasmodium falciparum infections and malaria clinical cases are reported during the dry season. This study aims to assess the relationship between IgG antibody (Ab) responses to gSG6-P1 mosquito salivary peptide and the prevalence of P. falciparum infection in children during the dry season in the Senegal River Valley. The positive association of the Ab response to gSG6-P1, as biomarker of human exposure to Anopheles vector bite, and P. falciparum infectious status (uninfected, infected-asymptomatic or infected-symptomatic) will allow considering this biomarker as a potential indicator of P. falciparum infection risk during the dry season.Microscopic examination of thick blood smears was performed in 371 and 310 children at the start (January) and at the end (June) of the dry season, respectively, in order to assess the prevalence of P. falciparum infection. Collected sera were used to evaluate IgG response to gSG6-P1 by ELISA. Association between parasitological and clinical data (infected-asymptomatic or infected-symptomatic) and the anti-gSG6-P1 IgG levels were evaluated during this period.The prevalence of P. falciparum infection was very low to moderate according to the studied period and was higher in January (23.5%) compared to June (3.5%). Specific IgG response was also different between uninfected children and asymptomatic carriers of the parasite. Children with P. falciparum infection in the dry season showed higher IgG Ab levels to gSG6-P1 than uninfected children.The results strengthen the hypothesis that malaria transmission is maintained during the dry season in an area of low and seasonal transmission. The measurement of IgG responses to gSG6-P1 salivary peptide could be a pertinent indicator of human malaria reservoir or infection risk in this particular epidemiological context. This promising immunological marker could be useful for the evaluation of the risk of P. falciparum exposure observed during dry season and, by consequences, could be used for the survey of potential pre-elimination situation.

SUBMITTER: Sagna AB

PROVIDER: S-EPMC3766161 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

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Plasmodium falciparum infection during dry season: IgG responses to Anopheles gambiae salivary gSG6-P1 peptide as sensitive biomarker for malaria risk in Northern Senegal.

Sagna André B AB Gaayeb Lobna L Sarr Jean B JB Senghor Simon S Poinsignon Anne A Boutouaba-Combe Samy S Schacht Anne-Marie AM Hermann Emmanuel E Faye Ngor N Remoue Franck F Riveau Gilles G

Malaria journal 20130830

<h4>Background</h4>The Northern part of Senegal is characterized by a low and seasonal transmission of malaria. However, some Plasmodium falciparum infections and malaria clinical cases are reported during the dry season. This study aims to assess the relationship between IgG antibody (Ab) responses to gSG6-P1 mosquito salivary peptide and the prevalence of P. falciparum infection in children during the dry season in the Senegal River Valley. The positive association of the Ab response to gSG6-P ...[more]

PMID: 23988032

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Project description:BACKGROUND:Mosquito saliva elicits immune responses in humans following mosquito blood feeding. Detection of human antibodies recognizing the Anopheles gambiae salivary gland protein 6 (gSG6) or the gSG6-P1 peptide in residents of Africa, South America and Southeast Asia suggested the potential for these antibodies to serve as a universal marker to estimate human biting rates. Validating the utility of this approach requires concurrent comparisons of anopheline biting rates with antibodies to the gSG6 protein to determine the sensitivity and specificity of the assay for monitoring changes in vector populations. This study investigated whether seroprevalence of anti-gSG6 antibodies in humans reflected the relative exposure to Anopheles farauti bites in the Solomon Islands as estimated from sympatric human landing catches. METHODS:Human biting rates by An. farauti were estimated by landing catches at 10 sampling sites in each of 4 villages during the wet and dry seasons. Human serum samples from these same villages were also collected during the wet and dry seasons and analysed for antibody recognition of the gSG6 antigen by the Luminex xMAP© platform. Antibody titres and prevalence were compared to HLCs at the sampling sites nearest to participants' residences for utility of anti-gSG6 antibodies to estimate human exposure to anopheline bites. RESULTS:In this study in the Solomon Islands only 11% of people had very high anti-gSG6 antibody titres, while other individuals did not recognize gSG6 despite nightly exposures of up to 190 bites by An. farauti. Despite clear spatial differences in the human biting rates within and among villages, associations between anti-gSG6 antibody titres and biting rates were not found. CONCLUSIONS:Few studies to date have concurrently measured anopheline biting rates and the prevalence of human antibodies to gSG6. The lack of association between anti-gSG6 antibody titres and concurrently measured human biting rates suggests that the assay for human anti-gSG6 antibodies lacks sufficient sensitivity to be a biomarker of An. farauti exposure at an epidemiologically relevant scale. These findings imply that an improvement in the sensitivity of serology to monitor changes in anopheline biting exposure may require the use of saliva antigens from local anophelines, and this may be especially true for species more distantly related to the African malaria vector An. gambiae.

Project description:Salivary proteins injected by blood feeding arthropods into their hosts evoke a saliva-specific humoral response which can be useful to evaluate exposure to bites of disease vectors. However, saliva of hematophagous arthropods is a complex cocktail of bioactive factors and its use in immunoassays can be misleading because of potential cross-reactivity to other antigens. Toward the development of a serological marker of exposure to Afrotropical malaria vectors we expressed the Anopheles gambiae gSG6, a small anopheline-specific salivary protein, and we measured the anti-gSG6 IgG response in individuals from a malaria hyperendemic area of Burkina Faso, West Africa. The gSG6 protein was immunogenic and anti-gSG6 IgG levels and/or prevalence increased in exposed individuals during the malaria transmission/rainy season. Moreover, this response dropped during the intervening low transmission/dry season, suggesting it is sensitive enough to detect variation in vector density. Members of the Fulani ethnic group showed higher anti-gSG6 IgG response as compared to Mossi, a result consistent with the stronger immune reactivity reported in this group. Remarkably, anti-gSG6 IgG levels among responders were high in children and gradually declined with age. This unusual pattern, opposite to the one observed with Plasmodium antigens, is compatible with a progressive desensitization to mosquito saliva and may be linked to the continued exposure to bites of anopheline mosquitoes. Overall, the humoral anti-gSG6 IgG response appears a reliable serological indicator of exposure to bites of the main African malaria vectors (An. gambiae, Anopheles arabiensis and, possibly, Anopheles funestus) and it may be exploited for malaria epidemiological studies, development of risk maps and evaluation of anti-vector measures. In addition, the gSG6 protein may represent a powerful model system to get a deeper understanding of molecular and cellular mechanisms underlying the immune tolerance and progressive desensitization to insect salivary allergens.

Project description:BACKGROUND: The Anopheles gambiae gSG6 is an anopheline-specific salivary protein which helps female mosquitoes to efficiently feed on blood. Besides its role in haematophagy, gSG6 is immunogenic and elicits in exposed individuals an IgG response, which may be used as indicator of exposure to the main African malaria vector A. gambiae. However, malaria transmission in tropical Africa is sustained by three main vectors (A. gambiae, Anopheles arabiensis and Anopheles funestus) and a general marker, reflecting exposure to at least these three species, would be especially valuable. The SG6 protein is highly conserved within the A. gambiae species complex whereas the A. funestus homologue, fSG6, is more divergent (80% identity with gSG6). The aim of this study was to evaluate cross-reactivity of human sera to gSG6 and fSG6. METHODS: The A. funestus SG6 protein was expressed/purified and the humoral response to gSG6, fSG6 and a combination of the two antigens was compared in a population from a malaria hyperendemic area of Burkina Faso where both vectors were present, although with a large A. gambiae prevalence (>75%). Sera collected at the beginning and at the end of the high transmission/rainy season, as well as during the following low transmission/dry season, were analysed. RESULTS: According to previous observations, both anti-SG6 IgG level and prevalence decreased during the low transmission/dry season and showed a typical age-dependent pattern. No significant difference in the response to the two antigens was found, although their combined use yielded in most cases higher IgG level. CONCLUSIONS: Comparative analysis of gSG6 and fSG6 immunogenicity to humans suggests the occurrence of a wide cross-reactivity, even though the two proteins carry species-specific epitopes. This study supports the use of gSG6 as reliable indicator of exposure to the three main African malaria vectors, a marker which may be useful to monitor malaria transmission and evaluate vector control measures, especially in conditions of low malaria transmission and/or reduced vector density. The Anopheles stephensi SG6 protein also shares 80% identity with gSG6, suggesting the attractive possibility that the A. gambiae protein may also be useful to assess human exposure to several Asian malaria vectors.

Project description:In order to improve malaria control, and under the aegis of WHO recommendations, many efforts are being devoted to developing new tools for identifying geographic areas with high risk of parasite transmission. Evaluation of the human antibody response to arthropod salivary proteins could be an epidemiological indicator of exposure to vector bites, and therefore to risk of pathogen transmission. In the case of malaria, which is transmitted only by anopheline mosquitoes, maximal specificity could be achieved through identification of immunogenic proteins specific to the Anopheles genus. The objective of the present study was to determine whether the IgG response to the Anopheles gambiae gSG6 protein, from its recombinant form to derived synthetic peptides, could be an immunological marker of exposure specific to Anopheles gambiae bites.Specific IgG antibodies to recombinant gSG6 protein were observed in children living in a Senegalese area exposed to malaria. With the objective of optimizing Anopheles specificity and reproducibility, we designed five gSG6-based peptide sequences using a bioinformatic approach, taking into consideration i) their potential antigenic properties and ii) the absence of cross-reactivity with protein sequences of other arthropods/organisms. The specific anti-peptide IgG antibody response was evaluated in exposed children. The five gSG6 peptides showed differing antigenic properties, with gSG6-P1 and gSG6-P2 exhibiting the highest antigenicity. However, a significant increase in the specific IgG response during the rainy season and a positive association between the IgG level and the level of exposure to Anopheles gambiae bites was significant only for gSG6-P1.This step-by-step approach suggests that gSG6-P1 could be an optimal candidate marker for evaluating exposure to Anopheles gambiae bites. This marker could be employed as a geographic indicator, like remote sensing techniques, for mapping the risk of malaria. It could also represent a direct criterion of efficacy in evaluation of vector control strategies.

Project description:Although the salivary transcriptome of adult mosquitoes has been thoroughly described in several recent papers, very little information exists regarding the biological role of larval salivary glands in the Culicidae. We used whole-transcriptome AffymetrixÂ® chips to compare the transcriptional profiles of Anopheles gambiae larval (L4) salivary glands and whole larvae. We identified a total of 277 transcripts as being significantly enriched in the salivary glands. Based on available annotation for the known or predicted protein sequences encoded by these transcripts, 41 were identified as corresponding to secreted proteins, 233 as corresponding to non-secreted (housekeeping) proteins, and 3 as encoding proteins of unknown function. Based on functional annotation of the putatively secreted gene products, we propose that larval salivary secretions have roles in nutrient digestion, detoxification, immunity, and mouthpart lubrication. Interestingly, several components of the larval saliva (e.g. apyrase and serine proteases) have also been reported to exist in adult female saliva, where they are though to help regulate a vertebrate hostâs immune response to bloodfeeding. In conclusion, our results suggest that the salivary glands are important components of both the digestive and immune systems of larval mosquitoes, and that their study might provide clues about the evolution of adaptations to bloodfeeding observed in adults. Experiment Overall Design: We attempted to identify transcripts that are both present and significantly enriched in the salivary glands (SG) of the 4th instar Anopheles gambiae larva. Transcripts were considered as present in the SG if the built-in Affymetrix detection call scored them as such in all three biological replicates of the experiment. Expression values (i.e. signal intensities) of transcripts from the salivary glands were compared to those of a matching group of whole 4th instar larvae using a t-test. Transcripts showing an expression value two-fold or higher (p < 0.01; false discovery rate=1%) in the SG as compared to whole larvae were considered to be significantly enriched.

Dataset Information

Plasmodium falciparum infection during dry season: IgG responses to Anopheles gambiae salivary gSG6-P1 peptide as sensitive biomarker for malaria risk in Northern Senegal.

Publications

Plasmodium falciparum infection during dry season: IgG responses to Anopheles gambiae salivary gSG6-P1 peptide as sensitive biomarker for malaria risk in Northern Senegal.

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