Evaluation of the antibody response to Anopheles salivary antigens as a potential marker of risk of malaria

Prevalence of culicine salivary antibodies in non-human primates living in national parks in Thailand

Macaques are widely distributed in Thailand with remarkable adaptation to living close to humans in residential, religious sites, markets and tourist areas. They play an essential role in the persistence of pathogens in the environment. As reservoir hosts, they are exposed to hematophagous vectors that secrete saliva, a cocktail of bioactive molecules including antigenic components stimulating host antibody production. Subsequent to the detection of mosquito-borne pathogens in macaques living in national parks, we aimed to determine the seroprevalence of antibodies to crude salivary gland extracts (SGEs) from culicine mosquitoes (Aedes aegypti [Linnaeus, 1762], Ae. albopictus [Skuse, 1895] and Culex quinquefasciatus [Say, 1823]) and compare individual titres between macaque species/national parks (33, Macaca arctoides [I. Geoffroy Saint-Hilaire, 1831] [Primates: Cercopithecidae] from Kaeng Krachan, 23 M. leonina leonina [Blyth, 1863] [Primates: Cercopithecidae] from Khao Yai and four M. fascicularis [Raffles, 1821] [Primates: Cercopithecidae] from Mu Ko Ranong). The anti-mosquito SGE antibodies found in 60 macaques from three national parks indicate varying levels of host-vector exposure. Macaque antibody titres were high against culicine mosquitoes. However, the significant difference among national parks (or macaque species) was only observed against Cx. quinquefasciatus. Correlation analysis of titres between Aedes SGE and arboviruses revealed a significantly more intense immune response against Ae. albopictus in DENV3-positive M. arctoides. Current findings support the concept of salivary biomarkers using accessible SGE, available from mosquito colonies of interest. However, we observed cross-reactivity between Aedes species because of crude SGE containing species-shared proteins. Nevertheless, a potential risk of pathogen transmission is emphasised between national park visitors and macaques via mosquitoes as bridge vectors. This information contributes to preventive measures against mosquito bites, including those implemented in tourist areas.

Human IgG responses to Anopheles gambiae immunogenic salivary proteins in urban and rural populations of Burkina Faso: biomarkers of exposure to malaria vector bites

BACKGROUND

Malaria control would be greatly facilitated by the development of new tools for rapidly assessing malaria transmission intensity. In malaria-endemic areas such as Burkina Faso, human populations are frequently exposed to immunomodulatory salivary components injected during mosquito blood feeding. Numerous studies have examined parasite immunity; however, there are few data available on vector immunity as a means of assessing malaria transmission in sub-Saharan Africa. The present study aims to compare IgG-specific response to salivary gland extracts (SGE) of Anopheles gambiae (An. gambiae) in populations living in urban and rural areas in Burkina Faso.

METHODS

A cross-sectional descriptive study was carried out in two sites, Ouagadougou city and Sapouy village, where blood samples (n = 676) from children (0-15 years) and adults were collected. After An. gambiae salivary protein isolation, the antibody (IgG) response to those SGE was evaluated by enzyme-linked immunosorbent assay (ELISA), representing a proxy of Anopheles exposure. The difference in antibody concentrations between groups was tested using parametric tests (Student's t-test and analysis of variance [ANOVA]) and the nonparametric Mann-Whitney U (Wilcoxon rank-sum) test. All differences were considered significant at P < 0.05.

RESULTS

The study population consisted of 63.0% males and 37.0% females (average age = 31.2 ± 17.8 years). IgG antibodies against An. gambiae salivary protein were detected in all study participants. Urban participants demonstrated a greater mean IgG level to An. gambiae bites than rural (P < 0.0001). The mean IgG level was higher in secondary school children compared with primary school children (P < 0.0001). Organic cotton farmers held higher IgG to An. gambiae bites than conventional cotton farmers (P = 0.0027).

CONCLUSIONS

The evaluation of IgG specific to mosquito salivary gland extracts as immunological biomarkers in populations in Burkina Faso allowed us to show that the human anti-SGE IgG level to An. gambiae bites is strongly influenced by the living environment and the use of insecticides in agriculture.

Human antibodies against Anopheles salivary proteins: emerging biomarkers of mosquito and malaria exposure

Antibodies developed against Anopheles mosquito salivary proteins injected during biting may serve as proxy biomarkers of Anopheles biting exposure. Anti-salivary biomarkers are being increasingly investigated, with ~60 studies published to date, mostly identifying positive associations with Anopheles human biting rates (HBRs). However, several literature gaps must be addressed to inform the application of anti-salivary biomarkers for serosurveillance of vector exposure and malaria transmission and in vector-control trials. We highlight the need for more studies that collect HBRs and antibody data contemporaneously, investigate novel antigens for non-African Anopheles species, and characterize antibody kinetics to understand how biomarkers can track changes in exposure over time. Together, these directions may improve upon insensitive manual mosquito catch techniques and strengthen malaria surveillance programs.

Two Mosquito Salivary Antigens Demonstrate Promise as Biomarkers of Recent Exposure to Plasmodium falciparum-Infected Mosquito Bites

BACKGROUND

Measuring malaria transmission intensity using the traditional entomological inoculation rate is difficult. Antibody responses to mosquito salivary proteins like SG6 have been used as biomarkers of exposure to Anopheles mosquito bites. Here, we investigate 4 mosquito salivary proteins as potential biomarkers of human exposure to mosquitoes infected with Plasmodium falciparum: mosGILT, SAMSP1, AgSAP, and AgTRIO.

METHODS

We tested population-level human immune responses in longitudinal and cross-sectional plasma from individuals with known P falciparum infection from low- and moderate-transmission areas in Senegal using a multiplexed magnetic bead-based assay.

RESULTS

AgSAP and AgTRIO were the best indicators of recent exposure to infected mosquitoes. Antibody responses to AgSAP, in a moderate-endemicity area, and to AgTRIO in both low- and moderate-endemicity areas, were significantly higher than nonendemic controls. No antibody responses significantly differed between low- and moderate-transmission areas, or between equivalent groups during and outside the malaria transmission seasons. AgSAP and AgTRIO reactivity peaked 2-4 weeks after clinical P falciparum infection and declined 3 months after infection.

CONCLUSIONS

Reactivity to AgSAP and AgTRIO reflects exposure to infectious mosquitoes or recent bites rather than general mosquito exposure, highlighting their promise for incorporation into multiplexed assays for serosurveillance of population-level changes in P falciparum-infected mosquito exposure.

Research progress toward arthropod salivary protein vaccine development for vector-borne infectious diseases

Hematophagous arthropods, including mosquitoes, ticks, and flies, are responsible for the transmission of several pathogens to vertebrates on whom they blood feed. The diseases caused by these pathogens, collectively known as vector-borne diseases (VBDs), threaten the health of humans and animals. In general, attempts to develop vaccines for pathogens transmitted by arthropods have met with moderate success, with few vaccine candidates currently developed. Nowadays, there are vaccine candidates under clinical trials, including different platforms, like mRNA, DNA, recombinant viral vector-based, virus-like particles (VLPs), inactivated-virus, live-attenuated virus, peptide and protein-based vaccines, all of them based on the presentation of pathogen antigens to the host immune system. A new approach to prevent VBDs has arose during the last decades, based on the design of vaccines that target vector-derived antigens. The salivary secretions of arthropods, in addition of causing allergic reactions and harbor pathogens, are also involved in the transmission and infection establishment in the host, altering its immune responses. In this review, we summarize the achievements in the arthropod salivary-based vaccine development for different vector-borne infectious diseases. This provides a rationale for creating vaccines against different types of arthropod salivary proteins, such as mosquitoes, ticks, and sand flies. Using salivary proteins of clinically important vectors might contribute to achieve protection against and control multiple arthropod-borne infection diseases.

The potential use of arginine kinase from the brown tick Rhipicephalus sanguineus as a biomarker for vector exposure in the surveillance of Rocky Mountain spotted fever

The brown dog tick (Rhipicephalus sanguineus) is the vector of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever (RMSF) in Northern Mexico and Southwestern United States. The immune response to a tick protein in the sera of humans or animals may reveal the zones with a high propensity to acquire RMSF, and vector control strategies may be focused on these zones. Arginine kinase (AK) is a highly antigenic invertebrate protein that may serve as a marker for tick exposure. We used R. sanguineus recombinant AK in an indirect ELISA assay with RMSF-positive patient sera. The response to AK was significantly higher against the sera of RMSF patients than the control sera from healthy participants without contact with dogs. To validate the antigenicity of tick AK, we mutated one predicted conformational epitope to alanine residues, which reduced the recognition by RMSF patients' immunoglobulins. This preliminary result opens a perspective towards the development of a complimentary technique based on RsAK as an antigen biomarker for vector serological surveillance for Rickettsia RMSF prevention.

Utility of plasma anti-gSG6-P1 IgG levels in determining changes in Anopheles gambiae bite rates in a rural area of Cameroon

The applicability of the specific human IgG antibody response to Anopheles gambiae salivary Gland Protein-6 peptide 1 (gSG6-P1 salivary peptide) as a biomarker able to distinguish the level of exposure to mosquito bites according to seasonal variations has not yet been evaluated in Central African regions. The study aimed to provide the first reliable data on the IgG anti-gSG6-P1 response in rural area in Cameroon according to the dry- and rainy-season. Between May and December 2020, dry blood samples were collected from people living in the Bankeng village in the forest area of the Centre region of Cameroon. Malaria infection was determined by thick-blood smear microscopy and multiplex PCR. The level of IgG anti-gSG6-P1 response, was assessed by enzyme-linked immunosorbent assay. Anopheles density and aggressiveness were assessed using human landing catches. The prevalence of malaria infection remains significantly higher in the rainy season than in the dry season (77.57% vs 61.44%; p = 0.0001). The specific anti-gSG6-P1 IgG response could be detected in individuals exposed to few mosquito bites and showed inter-individual heterogeneity even when living in the same exposure area. In both seasons, the level of anti-gSG6-P1 IgG response was not significantly different between Plasmodium infected and non-infected individuals. Mosquito bites were more aggressive in the rainy season compared to the dry season (human biting rate-HBR of 15.05 b/p/n vs 1.5 b/p/n) where mosquito density was very low. Infected mosquitoes were found only during the rainy season (sporozoite rate = 10.63% and entomological inoculation rate-EIR = 1.42 ib/p/n). The level of IgG anti-gSG6-P1 response was significantly higher in the rainy season and correlated with HBR (p ˂ 0.0001). This study highlights the high heterogeneity of individual's exposure to the Anopheles gambiae s.l vector bites depending on the transmission season in the same area. These findings reinforce the usefulness of the anti-gSG6-P1 IgG response as an accurate immunological biomarker for detecting individual exposure to Anopheles gambiae s.l. bites during the low risk period of malaria transmission in rural areas and for the differentiating the level of exposure to mosquitoes.

Two mosquito salivary antigens demonstrate promise as biomarkers of recent exposure to P. falciparum infected mosquito bites

Background

Measuring malaria transmission intensity using the traditional entomological inoculation rate is difficult. Antibody responses to mosquito salivary proteins such as SG6 have previously been used as biomarkers of exposure to Anopheles mosquito bites. Here, we investigate four mosquito salivary proteins as potential biomarkers of human exposure to mosquitoes infected with P. falciparum: mosGILT, SAMSP1, AgSAP, and AgTRIO.

Methods

We tested population-level human immune responses in longitudinal and cross-sectional plasma samples from individuals with known P. falciparum infection from low and moderate transmission areas in Senegal using a multiplexed magnetic bead-based assay.

Results

AgSAP and AgTRIO were the best indicators of recent exposure to infected mosquitoes. Antibody responses to AgSAP, in a moderate endemic area, and to AgTRIO in both low and moderate endemic areas, were significantly higher than responses in a healthy non-endemic control cohort (p-values = 0.0245, 0.0064, and <0.0001 respectively). No antibody responses significantly differed between the low and moderate transmission area, or between equivalent groups during and outside the malaria transmission seasons. For AgSAP and AgTRIO, reactivity peaked 2-4 weeks after clinical P. falciparum infection and declined 3 months after infection.

Discussion

Reactivity to both AgSAP and AgTRIO peaked after infection and did not differ seasonally nor between areas of low and moderate transmission, suggesting reactivity is likely reflective of exposure to infectious mosquitos or recent biting rather than general mosquito exposure. Kinetics suggest reactivity is relatively short-lived. AgSAP and AgTRIO are promising candidates to incorporate into multiplexed assays for serosurveillance of population-level changes in P. falciparum-infected mosquito exposure.

Comparing malaria risk exposure in rural Cambodia population using GPS tracking and questionnaires

BACKGROUND

The Great Mekong Subregion has attained a major decline in malaria cases and fatalities over the last years, but residual transmission hotspots remain, supposedly fueled by forest workers and migrant populations. This study aimed to: (i) characterize the fine-scale mobility of forest-goers and understand links between their daily movement patterns and malaria transmission, using parasites detection via real time polymerase chain reaction (RT PCR) and the individual exposure to Anopheles bites by quantification of anti-Anopheles saliva antibodies via enzyme-linked immunosorbent assay; (ii) assess the concordance of questionnaires and Global Positioning System (GPS) data loggers for measuring mobility.

METHODS

Two 28 day follow-ups during dry and rainy seasons, including a GPS tracking, questionnaires and health examinations, were performed on male forest goers representing the population at highest risk of infection. Their time spent in different land use categories and demographic data were analyzed in order to understand the risk factors driving malaria in the study area.

RESULTS

Malaria risk varied with village forest cover and at a resolution of only a few kilometers: participants from villages outside the forest had the highest malaria prevalence compared to participants from forest fringe's villages. The time spent in a specific environment did not modulate the risk of malaria, in particular the time spent in forest was not associated with a higher probability to detect malaria among forest-goers. The levels of antibody response to Anopheles salivary peptide among participants were significantly higher during the rainy season, in accordance with Anopheles mosquito density variation, but was not affected by sociodemographic and mobility factors. The agreement between GPS and self-reported data was only 61.9% in reporting each kind of visited environment.

CONCLUSIONS

In a context of residual malaria transmission which was mainly depicted by P. vivax asymptomatic infections, the implementation of questionnaires, GPS data-loggers and quantification of anti-saliva Anopheles antibodies on the high-risk group were not powerful enough to detect malaria risk factors associated with different mobility behaviours or time spent in various environments. The joint implementation of GPS trackers and questionnaires allowed to highlight the limitations of both methodologies and the benefits of using them together. New detection and follow-up strategies are still called for.

Mosquito allergy: Immunological aspects and clinical management

Mosquito allergy has been conceived as the cutaneous reactions that appears during and after mosquito biting process; a perception that is supported by several scientific research. Additional data have led to conceive that other manifestations of allergic responses may occur as a cause of the exposure to somatic mosquito allergens. Two main phenotypes of mosquito allergy are identifiable: the cutaneous allergic reactions, induced by salivary allergens, and other manifestations of the allergic responses such as asthma and allergic rhino conjunctivitis that are caused by somatic allergens. The cutaneous reactions have kept the focus of attention of the scientific community. It appears as skin lesions that resembles the phenotype of papular urticaria with a defined natural history of the disease. Although these two phenotypes of mosquito allergy seem to be well differentiated in terms of the allergens that are involved and the routes of exposures, other factors such as geographical distribution, may participate. Mosquitoes have adapted to the host immune response against bites, producing immunomodulatory molecules that counteract such defensive response. The role that the immunomodulatory molecules have on the allergic immune response has not been studied yet and it is still not known if affects all mosquito allergy phenotypes. Only a few studies of allergen specific immunotherapy for cutaneous allergic reactions induced by mosquito bites have been done, and none for respiratory allergic responses. The clinical practice focuses on symptom management and avoiding mosquito bites as much as possible. Avoiding mosquitoes, using different well described methods, is still the best option to limit contact with these insects. The lack of knowledge of mosquito allergy have raised several questions that affects the clinical management of this allergic disease, from its diagnosis, prevention and immunotherapy.

Characterizing antibody responses to mosquito salivary antigens of the Southeast Asian vectors of malaria and dengue with a human challenge model of controlled exposure: a protocol

Background: Measurement of antibody titers directed against mosquito salivary antigens in blood samples has been proposed as an outcome measure to assess human exposure to vector bites. However, only a handful of antigens have been identified and the specificity and longitudinal dynamics of antibody responses are not well known. We report the protocol of a clinical trial of controlled exposure to mosquito bites that aims to identify and validate biomarkers of exposure to bites of mosquito vector species that transmit malaria and dengue in Southeast Asia and some other parts of the world. Methods: This study is an exploratory factorial randomized control trial of controlled exposure to mosquito bites with 10 arms corresponding to different species ( Aedes aegypti, Ae. albopictus, Anopheles dirus, An. maculatus and An. minimus) and numbers of bites (35 or 305 bites in total over 6 weeks). Blood samples will be collected from study participants before, during and after mosquito biting challenges. Candidate peptides will be identified from published literature with antigen prediction algorithms using mosquito DNA sequence data and with immunoblotting assays carried out using protein extracts of dissected mosquito salivary glands and participants samples. Antibody titers against candidate peptides will be determined in participants samples with high-throughput cutting-edge immuno-assays. Quantification of the antibody response profile over time (including an estimate of the decay rate) and the effect of the number of bites on the antibody response will be determined using linear and logistic mixed-effects models for the continuous and the binary response, respectively. Conclusion: This research is expected to generate important knowledge for vector sero-surveillance and evaluation of vector-control interventions against malaria and dengue in the Greater Mekong Subregion. Registration: This study is registered with clinicaltrials.gov (NCT04478370) on July 20 ^th, 2020.

Characterizing antibody responses to mosquito salivary antigens of the Southeast Asian vectors of malaria and dengue with a human challenge model of controlled exposure: a protocol

Background: Measurement of antibody titers directed against mosquito salivary antigens in blood samples has been proposed as an outcome measure to assess human exposure to vector bites. However, only a handful of antigens have been identified and the specificity and longitudinal dynamics of antibody responses are not well known. We report the protocol of a clinical trial of controlled exposure to mosquito bites that aims to identify and validate biomarkers of exposure to bites of mosquito vector species that transmit malaria and dengue in Southeast Asia and some other parts of the world. Methods: This study is an exploratory factorial randomized control trial of controlled exposure to mosquito bites with 10 arms corresponding to different species (Aedes aegypt, Ae. albopictus, Anopheles dirus, An. maculatus and An. minimus) and numbers of bites (35 or 305 bites in total over 6 weeks). Blood samples will be collected from study participants before, during and after mosquito biting challenges. Candidate peptides will be identified from published literature with antigen prediction algorithms using mosquito DNA sequence data and with immunoblotting assays carried out using protein extracts of dissected mosquito salivary glands and participants samples. Antibody titers against candidate peptides will be determined in participants samples with high-throughput cutting-edge immuno-assays. Quantification of the antibody response profile over time (including an estimate of the decay rate) and the effect of the number of bites on the antibody response will be determined using linear and logistic mixed-effects models for the continuous and the binary response, respectively. Conclusion: This research is expected to generate important knowledge for vector sero-surveillance and evaluation of vector-control interventions against malaria and dengue in the Greater Mekong Subregion. Registration: This study is registered with clinicaltrials.gov (NCT04478370) on July 20th, 2020.

Evaluation of antibody responses to tsetse fly saliva in domestic animals in the sleeping sickness endemic foci of Bonon and Sinfra, Côte d'Ivoire

After intensive control efforts, human African trypanosomiasis (HAT) was declared eliminated in Côte d'Ivoire as a public health problem in December 2020 and the current objective is to achieve the interruption of the transmission (zero cases). Reaching this objective could be hindered by the existence of an animal reservoir of Trypanosoma (T.) brucei (b.) gambiense. In the framework of a study led in 2013 to assess the role of domestic animals in the epidemiology of HAT in the two last active foci from Côte d'Ivoire (Bonon and Sinfra), plasmas were sampled from four species of domestic animals for parasitological (microscopic examination by the buffy coat technique (BCT)), serological (immune trypanolysis (TL)) and molecular (specific PCR: TBR for T. brucei s.l., TCF for T. congolense forest type, TVW for T. vivax and PCR for T. b. gambiense) testing. In order to improve the understanding of the involvement/role of these animals in the transmission of T. b. gambiense, we have quantified in this study the IgG response to whole saliva extracts of Glossina palpalis gambiensis in order to perform an association analysis between anti-saliva responses and the positivity of diagnostic tests. Cattle and pigs had significantly higher rates of anti-tsetse saliva responses compared to goats and sheep (p < 0.01). In addition, the anti-tsetse saliva responses were strongly associated with the parasitology (BCT+), serology (TL+) and PCR (TBR+ and TCF+) results (p < 0.001). These associations indicate a high level of contacts between the positive/infected animals and tsetse flies. Our findings suggest that protecting cattle and pigs against tsetse bites could have a significant impact in reducing transmission of both animal and human trypanosome species, and advocates for a "One health" approach to better control African trypanosomosis in Côte d'Ivoire.

Human IgG responses to the Aedes albopictus 34k2 salivary protein: analyses in Réunion Island and Bolivia confirm its suitability as marker of host exposure to the tiger mosquito

BACKGROUND

The rapid worldwide spreading of Aedes aegypti and Aedes albopictus is expanding the risk of arboviral diseases transmission, pointing out the urgent need to improve monitoring and control of mosquito vector populations. Assessment of human-vector contact, currently estimated by classical entomological methods, is crucial to guide planning and implementation of control measures and evaluate transmission risk. Antibody responses to mosquito genus-specific salivary proteins are emerging as a convenient complementary tool for assessing host exposure to vectors. We previously showed that IgG responses to the Ae. albopictus 34k2 salivary protein (al34k2) allow detection of seasonal and geographic variation of human exposure to the tiger mosquito in two temperate areas of Northeast Italy. The main aim of this study was to confirm and extend these promising findings to tropical areas with ongoing arboviral transmission.

METHODS

IgG responses to al34k2 and to the Ae. aegypti orthologous protein ae34k2 were measured by ELISA in cohorts of subjects only exposed to Ae. albopictus (Réunion Island), only exposed to Ae. aegypti (Bolivia) or unexposed to both these vectors (North of France).

RESULTS AND CONCLUSION

Anti-al34k2 IgG levels were significantly higher in sera of individuals from Réunion Island than in unexposed controls, indicating that al34k2 may be a convenient and reliable proxy for whole saliva or salivary gland extracts as an indicator of human exposure to Ae. albopictus. Bolivian subjects, exposed to bites of Ae. aegypti, carried in their sera IgG recognizing the Ae. albopictus al34k2 protein, suggesting that this salivary antigen can also detect, even though with low sensitivity, human exposure to Ae. aegypti. On the contrary, due to the high background observed in unexposed controls, the recombinant ae34k2 appeared not suitable for the evaluation of human exposure to Aedes mosquitoes. Overall, this study confirmed the suitability of anti-al34k2 IgG responses as a specific biomarker of human exposure to Ae. albopictus and, to a certain extent, to Ae. aegypti. Immunoassays based on al34k2 are expected to be especially effective in areas where Ae. albopictus is the main arboviral vector but may also be useful in areas where Ae. albopictus and Ae. aegypti coexist.

Some Good and Some Bad: Sand Fly Salivary Proteins in the Control of Leishmaniasis and in Autoimmunity

Sand flies are hematophagous insects responsible for the transmission of vector-borne diseases to humans. Prominent among these diseases is Leishmaniasis that affects the skin and mucous surfaces and organs such as liver and spleen. Importantly, the function of blood-sucking arthropods goes beyond merely transporting pathogens. The saliva of vectors of disease contains pharmacologically active components that facilitate blood feeding and often pathogen establishment. Transcriptomic and proteomic studies have enumerated the repertoire of sand fly salivary proteins and their potential use for the control of Leishmaniasis, either as biomarkers of vector exposure or as anti-Leishmania vaccines. However, a group of specific sand fly salivary proteins triggers formation of cross-reactive antibodies that bind the ectodomain of human desmoglein 1, a member of the epidermal desmosomal cadherins. These cross-reactive antibodies are associated with skin autoimmune blistering diseases, such as pemphigus, in certain immunogenetically predisposed individuals. In this review, we focus on two different aspects of sand fly salivary proteins in the context of human disease: The good, which refers to salivary proteins functioning as biomarkers of exposure or as anti-Leishmania vaccines, and the bad, which refers to salivary proteins as environmental triggers of autoimmune skin diseases.

Characterization of Anopheles gambiae D7 salivary proteins as markers of human-mosquito bite contact

BACKGROUND

Malaria is transmitted when infected Anopheles mosquitoes take a blood meal. During this process, the mosquitoes inject a cocktail of bioactive proteins that elicit antibody responses in humans and could be used as biomarkers of exposure to mosquito bites. This study evaluated the utility of IgG responses to members of the Anopheles gambiae D7 protein family as serological markers of human-vector contact.

METHODS

The D7L2, D7r1, D7r2, D7r3, D7r4 and SG6 salivary proteins from An. gambiae were expressed as recombinant antigens in Escherichia coli. Antibody responses to the salivary proteins were compared in Europeans with no prior exposure to malaria and lifelong residents of Junju in Kenya and Kitgum in Uganda where the intensity of malaria transmission is moderate and high, respectively. In addition, to evaluate the feasibility of using anti-D7 IgG responses as a tool to evaluate the impact of vector control interventions, we compared responses between individuals using insecticide-treated bednets to those who did not in Junju, Kenya where bednet data were available.

RESULTS

We show that both the long and short forms of the D7 salivary gland antigens elicit a strong antibody response in humans. IgG responses against the D7 antigens reflected the transmission intensities of the three study areas, with the highest to lowest responses observed in Kitgum (northern Uganda), Junju (Kenya) and malaria-naïve Europeans, respectively. Specifically, the long form D7L2 induced an IgG antibody response that increased with age and that was lower in individuals who slept under a bednet, indicating its potential as a serological tool for estimating human-vector contact and monitoring the effectiveness of vector control interventions.

CONCLUSIONS

This study reveals that D7L2 salivary antigen has great potential as a biomarker of exposure to mosquito bites and as a tool for assessing the efficacy of vector control strategies such as bednet use.

Anopheles salivary antigens as serological biomarkers of vector exposure and malaria transmission: A systematic review with multilevel modelling

Background

Entomological surveillance for malaria is inherently resource-intensive and produces crude population-level measures of vector exposure which are insensitive in low-transmission settings. Antibodies against Anopheles salivary proteins measured at the individual level may serve as proxy biomarkers for vector exposure and malaria transmission, but their relationship is yet to be quantified.

Methods

A systematic review of studies measuring antibodies against Anopheles salivary antigens (PROSPERO: CRD42020185449). Multilevel modelling (to account for multiple study-specific observations [level 1], nested within study [level 2], and study nested within country [level 3]) estimated associations between seroprevalence with Anopheles human biting rate (HBR) and malaria transmission measures.

Results

From 3981 studies identified in literature searches, 42 studies across 16 countries were included contributing 393 study-specific observations of anti-Anopheles salivary antibodies determined in 42,764 samples. A positive association between HBR (log transformed) and seroprevalence was found; overall a twofold (100% relative) increase in HBR was associated with a 23% increase in odds of seropositivity (OR: 1.23, 95% CI: 1.10-1.37; p<0.001). The association between HBR and Anopheles salivary antibodies was strongest with concordant, rather than discordant, Anopheles species. Seroprevalence was also significantly positively associated with established epidemiological measures of malaria transmission: entomological inoculation rate, Plasmodium spp. prevalence, and malarial endemicity class.

Conclusions

Anopheles salivary antibody biomarkers can serve as a proxy measure for HBR and malaria transmission, and could monitor malaria receptivity of a population to sustain malaria transmission. Validation of Anopheles species-specific biomarkers is important given the global heterogeneity in the distribution of Anopheles species. Salivary biomarkers have the potential to transform surveillance by replacing impractical, inaccurate entomological investigations, especially in areas progressing towards malaria elimination.

Funding

Australian National Health and Medical Research Council, Wellcome Trust.

First evaluation of antibody responses to Culex quinquefasciatus salivary antigens as a serological biomarker of human exposure to Culex bites: A pilot study in Côte d'Ivoire

Background

Culex mosquitoes are vectors for a variety of pathogens of public health concern. New indicators of exposure to Culex bites are needed to evaluate the risk of transmission of associated pathogens and to assess the efficacy of vector control strategies. An alternative to entomological indices is the serological measure of antibodies specific to mosquito salivary antigens. This study investigated whether the human IgG response to both the salivary gland extract and the 30 kDa salivary protein of Culex quinquefasciatus may represent a proxy of human exposure to Culex bites.

Methodology/Principal findings

A multidisciplinary survey was conducted with children aged 1 to 14 years living in neighborhoods with varying exposure to Culex quinquefasciatus in the city of Bouaké, Côte d’Ivoire. Children living in sites with high exposure to Cx quinquefasciatus had a significantly higher IgG response to both salivary antigens compared with children living in the control site where only very few Culex were recorded. Moreover, children from any Culex-high exposed sites had significantly higher IgG responses only to the salivary gland extract compared with children from the control village, whereas no difference was noted in the anti-30 kDa IgG response. No significant differences were noted in the specific IgG responses between age and gender. Sites and the use of a bed net were associated with the level of IgG response to the salivary gland extract and to the 30 kDa antigen, respectively.

Conclusions/Significance

These findings suggest that the IgG response to Culex salivary gland extracts is suitable as proxy of exposure; however, the specificity to the Culex genus needs further investigation. The lower antigenicity of the 30 kDa recombinant protein represents a limitation to its use. The high specificity of this protein to the Culex genus makes it an attractive candidate and other specific antibody responses might be more relevant as a biomarker of exposure. These epidemiological observations may form a starting point for additional work on developing serological biomarkers of Culex exposure.

The evaluation of exposure to mosquitoes is a key parameter in assessing the risk of transmission of associated pathogens, including zoonoses. Entomological methods represent the gold standard but have several limitations, and efforts are being made to develop new indicators to accurately assess human–Culex contact. This study showed the IgG response to Culex quinquefasciatus salivary gland extract is suitable proxy of exposure to Culex bites. The lower antigenicity of the 30 kDa recombinant protein represents a limitation to its use. The high specificity of this protein to the Culex genus makes it an attractive candidate and other isotypic antibody responses specific to this salivary antigen might be more relevant as a biomarker of exposure.

Serological biomarker for assessing human exposure to Aedes mosquito bites during a randomized vector control intervention trial in northeastern Thailand

Background

Aedes mosquitoes are vectors for several major arboviruses of public health concern including dengue viruses. The relationships between Aedes infestation and disease transmission are complex wherein the epidemiological dynamics can be difficult to discern because of a lack of robust and sensitive indicators for predicting transmission risk. This study investigates the use of anti-Aedes saliva antibodies as a serological biomarker for Aedes mosquito bites to assess small scale variations in adult Aedes density and dengue virus (DENV) transmission risk in northeastern Thailand. Individual characteristics, behaviors/occupation and socio-demographics, climatic and epidemiological risk factors associated with human-mosquito exposure are also addressed.

Methods

The study was conducted within a randomized clustered control trial in Roi Et and Khon Kaen provinces over a consecutive 19 months period. Thirty-six (36) clusters were selected, each of ten houses. Serological and entomological surveys were conducted in all houses every four months and monthly in three sentinel households per cluster between September 2017 and April 2019 for blood spot collections and recording concurrent immature and adult Aedes indices. Additionally, the human exposure to Aedes mosquito bites (i.e., Mosquito Exposure Index or MEI) was estimated by ELISA measuring levels of human antibody response to the specific Nterm-34 kDa salivary antigen. The relationships between the MEI, vector infestation indices (adult and immature stages) and vector DENV infection were evaluated using a two-level (house and individual levels) mixed model analysis with one-month lag autoregressive correlation.

Results

There was a strong positive relationship between the MEI and adult Aedes (indoor and outdoor) density. Individuals from households with a medium mosquito density (mean difference: 0.091, p<0.001) and households with a high mosquito density (mean difference: 0.131, p<0.001) had higher MEI’s compared to individuals from households without Aedes. On a similar trend, individuals from households with a low, medium or high indoor Aedes densities (mean difference: 0.021, p<0.007, 0.053, p<0.0001 and 0.037, p<0.0001 for low, medium and high levels of infestation, respectively) had higher MEI than individuals from houses without indoor Aedes. The MEI was driven by individual characteristics, such as gender, age and occupation/behaviors, and varied according to climatic, seasonal factors and vector control intervention (p<0.05). Nevertheless, the study did not demonstrate a clear correlation between MEI and the presence of DENV-infected Aedes.

Conclusion

This study represents an important step toward the validation of the specific IgG response to the Aedes salivary peptide Nterm-34kDa as a proxy measure for Aedes infestation levels and human-mosquito exposure risk in a dengue endemic setting. The use of the IgG response to the Nterm-34 kDa peptide as a viable diagnostic tool for estimating dengue transmission requires further investigations and validation in other geographical and transmission settings.

Aedes mosquitoes and the viruses they transmit are major public health concerns for over half of the global human population. However, the quantitative relationships between virus transmission and vector mosquito infestation remain unclear despite numerous indicators used to estimate transmission risk and predict dengue outbreaks. The aim of this study is to investigate the use of a salivary biomarker to assess the small-scale variation in human exposure to Aedes bites and the risk of dengue infection in the context of a vector control intervention in northeastern Thailand. A cohort of 539 persons visited every four months, including 161 individuals visited monthly, were recruited for routine serological and concurrent household entomological surveys during 19 consecutive months follow-up. Antibody response to Aedes bites was measured by enzyme-linked immunosorbent assays to assess the mosquito exposure index (MEI) and association with the Aedes adult and immature abundance as well as the presence of dengue virus (DENV) in adult mosquitoes (transmission risk). Additionally, the individual (cohort), climatic, and vector control intervention risk factors associated with MEI are explored. This study demonstrates that the MEI was strongly related to household adult Aedes density, particularly indoors resting mosquitoes. Additionally, the MEI was influenced by individual characteristics (i.e., person age, gender, staying indoors), and varied according to seasons and intervention. Nonetheless, no clear relationship between MEI and dengue transmission risk (i.e., vector infection) was detected. This study demonstrated the potential usefulness of the MEI to assess heterogeneity in adult Aedes infestation indices that could assist public health authorities to rapidly identify mosquito “hot spots” and the timeliness of effective vector control interventions.

Vector saliva controlled inflammatory response of the host may represent the Achilles heel during pathogen transmission

Infection with vector-borne pathogens starts with the inoculation of these pathogens during blood feeding. In endemic regions, the population is regularly bitten by naive vectors, implicating a permanent stimulation of the immune system by the vector saliva itself (pre-immune context). Comparatively, the number of bites received by exposed individuals from non-infected vectors is much higher than the bites from infected ones. Therefore, vector saliva and the immunological response in the skin may play an important role, so far underestimated, in the establishment of anti-pathogen immunity in endemic areas. Hence, the parasite biology and the disease pathogenesis in “saliva-primed” and “saliva-unprimed” individuals must be different. This integrated view on how the pathogen evolves within the host together with vector salivary components, which are known to be endowed with a variety of pharmacological and immunological properties, must remain the focus of any investigational study dealing with vector-borne diseases.

Considering this three-way partnership, the host skin (immune system), the pathogen, and the vector saliva, the approach that consists in the validation of vector saliva as a source of molecular entities with anti-disease vaccine potential has been recently a subject of active and fruitful investigation. As an example, the vaccination with maxadilan, a potent vasodilator peptide extracted from the saliva of the sand fly Lutzomyia longipalpis, was able to protect against infection with various leishmanial parasites. More interestingly, a universal mosquito saliva vaccine that may potentially protect against a range of mosquito-borne infections including malaria, dengue, Zika, chikungunya and yellow fever. In this review, we highlight the key role played by the immunobiology of vector saliva in shaping the outcome of vector-borne diseases and discuss the value of studying diseases in the light of intimate cross talk among the pathogen, the vector saliva, and the host immune mechanisms.

Preliminary validation of the use of IgG antibody response to Anopheles gSG6-p1 salivary peptide to assess human exposure to malaria vector bites in two endemic areas of Cameroon in Central Africa

The specific immune response to the Anopheles salivary peptide could be a pertinent and complementary tool to assess the risk of malaria transmission and the effectiveness of vector control strategies. This study aimed to obtain first reliable data on the current state of the Anopheles gSG6-P1 biomarker for assess the level of exposure to Anopheles bites in high malaria endemic areas in Cameroon. Blood smears were collected from people living in the neighborhoods of Youpwe (suburban area, continental) and Manoka (rural area, Island), both areas in the coastal region of Cameroon. Malaria infection was determined using thick blood smear microscopy, whereas the level of specific IgG response to gSG-P1 peptide was assessed by enzyme-linked immunosorbent assay from the dried blood spots. Of 266 (153 from Youpwe, 113 from Manoka) malaria endemic residents (mean age: 22.8±19.8 years, age range: 6 months–94 years, male/female sex ratio: 1/1.2, with Manoka mean age: 23.71±20.53, male/female sex ratio:1/1.13 and Youpwe mean age: 22.12±19.22, male/female sex ratio 1/0.67) randomly included in the study, Plasmodium infection prevalence was significantly higher in Manoka than in Youpwe (64.6% vs 12,4%, p = 0.0001). The anti-gSG6-P1 IgG response showed a high inter-individual heterogeneity and was significantly higher among individuals from Manoka than those from Youpwe (p = 0.023). Malaria infected individuals presented a higher anti-gSG6-P1 IgG antibody response than non-infected (p = 0.0004). No significant difference in the level of specific IgG response to gSG-P1 was observed according to long lasting insecticidal nets use. Taken together, the data revealed that human IgG antibody response to Anopheles gSG-P1 salivary peptide could be also used to assess human exposure to malaria vectors in Central African region. This finding strengthens the relevance of this candidate biomarker to be used for measuring human exposure to malaria vectors worldwide.

The Effects of A Mosquito Salivary Protein on Sporozoite Traversal of Host Cells

Malaria begins when Plasmodium-infected Anopheles mosquitoes take a blood meal on a vertebrate. During the initial probing process, mosquitoes inject saliva and sporozoites into the host skin. Components of mosquito saliva have the potential to influence sporozoite functionality. Sporozoite-associated mosquito saliva protein 1 (SAMSP1; AGAP013726) was among several proteins identified when sporozoites were isolated from saliva, suggesting it may have an effect on Plasmodium. Recombinant SAMSP1 enhanced sporozoite gliding and cell traversal activity in vitro. Moreover, SAMSP1 decreased neutrophil chemotaxis in vivo and in vitro, thereby also exerting an influence on the host environment in which the sporozoites reside. Active or passive immunization of mice with SAMSP1 or SAMSP1 antiserum diminished the initial Plasmodium burden after infection. Passive immunization of mice with SAMSP1 antiserum also added to the protective effect of a circumsporozoite protein monoclonal antibody. SAMSP1 is, therefore, a mosquito saliva protein that can influence sporozoite infectivity in the vertebrate host.

Complex relationships between Aedes vectors, socio-economics and dengue transmission-Lessons learned from a case-control study in northeastern Thailand

BACKGROUND/OBJECTIVES

Dengue fever is an important public health concern in most tropical and subtropical countries, and its prevention and control rest on vector surveillance and control. However, many aspects of dengue epidemiology remain unclear; in particular, the relationship between Aedes vector abundance and dengue transmission risk. This study aims to identify entomological and immunological indices capable of discriminating between dengue case and control (non-case) houses, based on the assessment of candidate indices, as well as individual and household characteristics, as potential risk factors for acquiring dengue infection.

METHODS

This prospective, hospital-based, case-control study was conducted in northeastern Thailand between June 2016 and August 2019. Immature and adult stage Aedes were collected at the houses of case and control patients, recruited from district hospitals, and at patients' neighboring houses. Blood samples were tested by RDT and PCR to detect dengue cases, and were processed with the Nterm-34 kDa salivary peptide to measure the human immune response to Aedes bites. Socioeconomic status, and other individual and household characteristics were analyzed as potential risk factors for dengue.

RESULTS

Study findings showed complex relationships between entomological indices and dengue risk. The presence of DENV-infected Aedes at the patient house was associated with 4.2-fold higher odds of dengue. On the other hand, Aedes presence (irrespective of infectious status) in the patient's house was negatively associated with dengue. In addition, the human immune response to Aedes bites, was higher in control than in case patients and Aedes adult abundance and immature indices were higher in control than in case houses at the household and the neighboring level. Multivariable analysis showed that children aged 10-14 years old and those aged 15-25 years old had respectively 4.5-fold and 2.9-fold higher odds of dengue infection than those older than 25 years.

CONCLUSION

DENV infection in female Aedes at the house level was positively associated with dengue infection, while adult Aedes presence in the household was negatively associated. This study highlights the potential benefit of monitoring dengue viruses in Aedes vectors. Our findings suggest that monitoring the presence of DENV-infected Aedes mosquitoes could be a better indicator of dengue risk than the traditional immature entomological indices.

Stratifying malaria receptivity in Bangladesh using archived rapid diagnostic tests

Background

Surveillance of low-density infections and of exposure to vectors is crucial to understand where malaria elimination might be feasible, and where the risk of outbreaks is high. Archived rapid diagnostic tests (RDTs), used by national malaria control and elimination programs for clinical diagnosis, present a valuable, yet rarely used resource for in-depth studies on malaria epidemiology.

Methods

1022 RDTs from two sub-Districts in Bangladesh (Alikadam and Kamalganj) were screened by qPCR for low-density Plasmodium falciparum and Plasmodium vivax infections, and by ELISA for Anopheles salivary gland antibodies as a marker for exposure to vectors.

Results

Concordance between RDT and qPCR was moderate. qPCR detected 31/1022 infections compared to 36/1022 diagnosed by RDT. Exposure to Anopheles was significantly higher in Kamalganj despite low transmission, which could be explained by low bed net use.

Conclusions

Archived RDTs present a valuable source of antibodies for serological studies on exposure to vectors. In contrast, the benefit of screening archived RDTs to obtain a better estimate of clinical case numbers is moderate. Kamalganj could be prone to outbreaks.

IgG Antibody Responses to the Aedes albopictus 34k2 Salivary Protein as Novel Candidate Marker of Human Exposure to the Tiger Mosquito

Mosquitoes of the Aedes genus transmit arboviruses of great importance to human health as dengue, chikungunya, Zika and yellow fever. The tiger mosquito Aedes albopictus can play an important role as arboviral vector, especially when Aedes aegypti is absent or present at low levels. Remarkably, the rapid worldwide spreading of the tiger mosquito is expanding the risk of arboviral transmission also to temperate areas, and the autochthonous cases of chikungunya, dengue and Zika in Europe emphasize the need for improved monitoring and control. Proteomic and transcriptomic studies on blood feeding arthropod salivary proteins paved the way toward the exploitation of genus-specific mosquito salivary proteins for the development of novel tools to evaluate human exposure to mosquito bites. We previously found that the culicine-specific 34k2 salivary protein from Ae. albopictus (al34k2) evokes specific IgG responses in experimentally exposed mice, and provided preliminary evidence of its immunogenicity to humans. In this study we measured IgG responses to al34k2 and to Ae. albopictus salivary gland protein extracts (SGE) in individuals naturally exposed to the tiger mosquito. Sera were collected in two areas of Northeast Italy (Padova and Belluno) during two different time periods: at the end of the low- and shortly after the high-density mosquito seasons. Anti-SGE and anti-al34k2 IgG levels increased after the summer period of exposure to mosquito bites and were higher in Padova as compared to Belluno. An age-dependent decrease of anti-saliva IgG responses was found especially in Padova, an area with at least 25 years history of Ae. albopictus colonization. Moreover, a weak correlation between anti-saliva IgG levels and individual perception of mosquito bites by study participants was found. Finally, determination of anti-al34k2 IgG1 and IgG4 levels indicated a large predominance of IgG1 antibodies. Overall, this study provides a convincing indication that antibody responses to al34k2 may be regarded as a reliable candidate marker to detect temporal and/or spatial variation of human exposure to Ae. albopictus; a serological tool of this kind may prove useful both for epidemiological studies and to estimate the effectiveness of anti-vectorial measures.

Identification and Pilot Evaluation of Salivary Peptides from Anopheles albimanus as Biomarkers for Bite Exposure and Malaria Infection in Colombia

Insect saliva induces significant antibody responses associated with the intensity of exposure to bites and the risk of disease in humans. Several salivary biomarkers have been characterized to determine exposure intensity to Old World Anopheles mosquito species. However, new tools are needed to quantify the intensity of human exposure to Anopheles bites and understand the risk of malaria in low-transmission areas in the Americas. To address this need, we conducted proteomic and bioinformatic analyses of immunogenic candidate proteins present in the saliva of uninfected Anopheles albimanus from two separate colonies—one originating from Central America (STECLA strain) and one originating from South America (Cartagena strain). A ~65 kDa band was identified by IgG antibodies in serum samples from healthy volunteers living in a malaria endemic area in Colombia, and a total of five peptides were designed from the sequences of two immunogenic candidate proteins that were shared by both strains. ELISA-based testing of human IgG antibody levels against the peptides revealed that the transferrin-derived peptides, TRANS-P1, TRANS-P2 and a salivary peroxidase peptide (PEROX-P3) were able to distinguish between malaria-infected and uninfected groups. Interestingly, IgG antibody levels against PEROX-P3 were significantly lower in people that have never experienced malaria, suggesting that it may be a good marker for mosquito bite exposure in naïve populations such as travelers and deployed military personnel. In addition, the strength of the differences in the IgG levels against the peptides varied according to location, suggesting that the peptides may able to detect differences in intensities of bite exposure according to the mosquito population density. Thus, the An. albimanus salivary peptides TRANS-P1, TRANS-P2, and PEROX-P3 are promising biomarkers that could be exploited in a quantitative immunoassay for determination of human-vector contact and calculation of disease risk.

Analysis in a murine model points to IgG responses against the 34k2 salivary proteins from Aedes albopictus and Aedes aegypti as novel promising candidate markers of host exposure to Aedes mosquitoes

Background

Aedes mosquitoes are vectors of arboviral diseases of great relevance for public health. The recent outbreaks of dengue, Zika, chikungunya and the rapid worldwide spreading of Aedes albopictus emphasize the need for improvement of vector surveillance and control. Host antibody response to mosquito salivary antigens is emerging as a relevant additional tool to directly assess vector-host contact, monitor efficacy of control interventions and evaluate risk of arboviral transmission.

Methodology/principal findings

Groups of four BALB/c mice were immunized by exposure to bites of either Aedes albopictus or Aedes aegypti. The 34k2 salivary proteins from Ae. albopictus (al34k2) and Ae. aegypti (ae34k2) were expressed in recombinant form and Ae. albopictus salivary peptides were designed through B-cell epitopes prediction software. IgG responses to salivary gland extracts, peptides, al34k2 and ae34k2 were measured in exposed mice. Both al34k2 and ae34k2, with some individual and antigen-specific variation, elicited a clearly detectable antibody response in immunized mice. Remarkably, the two orthologous proteins showed very low level of immune cross-reactivity, suggesting they may eventually be developed as species-specific markers of host exposure. The al34k2 immunogenicity and the limited immune cross-reactivity to ae34k2 were confirmed in a single human donor hyperimmune to Ae. albopictus saliva.

Conclusions/significance

Our study shows that exposure to bites of Ae. albopictus or Ae. aegypti evokes in mice species-specific IgG responses to al34k2 or ae34k2, respectively. Deeper understanding of duration of antibody response and validation in natural conditions of human exposure to Aedes mosquitoes are certainly needed. However, our findings point to the al34k2 salivary protein as a promising potential candidate for the development of immunoassays to evaluate human exposure to Ae. albopictus. This would be a step forward in the establishment of a serological toolbox for the simultaneous assessment of human exposure to Aedes vectors and the pathogens they transmit.

Taking advantage of several factors, as worldwide trading, climatic changes and urbanization, Aedes mosquitoes are impressively expanding their geographic distribution. A paradigm is provided by the rapid global spreading of Aedes albopictus, a species that is a competent vector of several arboviral diseases (e.g. dengue, Zika, chikungunya) and has been responsible of quite a few outbreaks in the last decade. Historically, vector control always played a pivotal role for the containment of arthropod-borne diseases, and this appears especially crucial for arboviral diseases for which no effective vaccines or specific medications are available. Currently, host exposure to mosquitoes is indirectly evaluated by entomological methods; however, exploitation of human immune responses to mosquito salivary proteins is emerging as a relevant additional tool, with important epidemiological implications for the evaluation of mosquito-borne disease risk. This study provides preliminary but solid indications that the 34k2 salivary proteins from Ae. albopictus and Aedes aegypti may be suitable candidates for the development of serological assays to evaluate spatial and/or temporal variation of human exposure to Aedes vectors. Combined to the presently available tools to assess arboviral exposure/infection, this may be of great help for the development of a serological toolbox allowing for the simultaneous determination of human exposure to Aedes vectors and to the pathogens they transmit.

Human exposure to Anopheles farauti bites in the Solomon Islands is not associated with IgG antibody response to the gSG6 salivary protein of Anopheles gambiae

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.

IgG1 and IgG4 antibodies against Aedes aegypti salivary proteins and risk for dengue infections

Dengue virus (DENV) is an arbovirus responsible for a significant number of deaths in Latin America. This virus is transmitted through the bite of Aedes aegypti, the main mosquito vector, and Ae. albopictus. During blood uptake, the mosquito injects its saliva into the host to facilitate the feeding process. Mosquito saliva contains potent immunogens capable of inducing antibody production directly related to mosquito bite exposure intensity and disease risk. In this study, we first determined the DENV infection status by two different DENV non-structural protein 1 (NS1) based rapid tests and qRT-PCR, then measured the levels of IgG1 and IgG4 antibodies against salivary proteins of Ae. aegypti female mosquitoes in volunteers living in a dengue endemic area. Our results show that people with a positive DENV diagnosis present higher levels of IgG4 antibodies than people with a negative diagnostic test, and that these antibody levels were higher in people with secondary DENV infections. With this study, we show that detection of IgG4 antibodies against mosquito saliva may be a reliable method to evaluate the risk of dengue infection.

New Immuno-Epidemiological Biomarker of Human Exposure to Aedes Vector Bites: From Concept to Applications

Arthropod-borne viruses (arboviruses) such as dengue virus (DENV), chikungunya virus (CHIKV), Zika virus (ZIKV), and yellow fever virus (YFV) are the most important 'emerging pathogens' because of their geographic spread and their increasing impact on vulnerable human populations. To fight against these arboviruses, vector control strategies (VCS) remain one of the most valuable means. However, their implementation and monitoring are labour intensive and difficult to sustain on large scales, especially when transmission and Aedes mosquito densities are low. To increase the efficacy of VCS, current entomological methods should be improved by new complementary tools which measure the risk of arthropod-borne diseases' transmission. The study of human⁻Aedes immunological relationships can provide new promising serological tools, namely antibody-based biomarkers, allowing to accurately estimate the human⁻Aedes contact and consequently, the risk of transmission of arboviruses and the effectiveness of VCS. This review focuses on studies highlighting the concept, techniques, and methods used to develop and validate specific candidate biomarkers of human exposure to Aedes bites. Potential applications of such antibody-based biomarkers of exposure to Aedes vector bites in the field of operational research are also discussed.

A mosquito salivary gland protein partially inhibits Plasmodium sporozoite cell traversal and transmission

The key step during the initiation of malaria is for motile Plasmodium parasites to exit the host dermis and infect the liver. During transmission, the parasites in the form of sporozoites, are injected together with mosquito saliva into the skin. However, the contribution of vector saliva to sporozoite activity during the establishment of the initial infection of the liver is poorly understood. Here we identify a vector protein by mass spectrometry, with similarity to the human gamma interferon inducible thiol reductase (GILT), that is associated with saliva sporozoites of infected Anopheles mosquitoes and has a negative impact on the speed and cell traversal activity of Plasmodium. This protein, referred to as mosquito GILT (mosGILT) represents an example of a protein found in mosquito saliva that may negatively influence sporozoite movement in the host and could lead to new approaches to prevent malaria.

Specific human antibody responses to Aedes aegypti and Aedes polynesiensis saliva: A new epidemiological tool to assess human exposure to disease vectors in the Pacific

BACKGROUND

Aedes mosquitoes severely affect the health and wellbeing of human populations by transmitting infectious diseases. In French Polynesia, Aedes aegypti is the main vector of dengue, chikungunya and Zika, and Aedes polynesiensis the primary vector of Bancroftian filariasis and a secondary vector of arboviruses. Tools for assessing the risk of disease transmission or for measuring the efficacy of vector control programmes are scarce. A promising approach to quantify the human-vector contact relies on the detection and the quantification of antibodies directed against mosquito salivary proteins.

METHODOLOGY/PRINCIPAL FINDINGS

An ELISA test was developed to detect and quantify the presence of immunoglobulin G (IgG) directed against proteins from salivary gland extracts (SGE) of Ae. aegypti and Ae. polynesiensis in human populations exposed to either species, through a cross-sectional study. In Tahiti and Moorea islands where Ae. aegypti and Ae. polynesiensis are present, the test revealed that 98% and 68% of individuals have developed IgG directed against Ae. aegypti and Ae. polynesiensis SGE, respectively. By comparison, ELISA tests conducted on a cohort of people from metropolitan France, not exposed to these Aedes mosquitoes, indicated that 97% of individuals had no IgG directed against SGE of either mosquito species. The analysis of additional cohorts representing different entomological Aedes contexts showed no ELISA IgG cross-reactivity between Ae. aegypti and Ae. polynesiensis SGE.

CONCLUSIONS/SIGNIFICANCE

The IgG response to salivary gland extracts seems to be a valid and specific biomarker of human exposure to the bites of Ae. aegypti and Ae. polynesiensis. This new immuno-epidemiological tool will enhance our understanding of people exposure to mosquito bites, facilitate the identification of areas where disease transmission risk is high and permit to evaluate the efficacy of novel vector control strategies in Pacific islands and other tropical settings.

Assessing naturally acquired immune response and malaria treatment outcomes in Lagos, Nigeria

Background: There are emerging reports of poor efficacy of artemisinin-based combination treatment (ACT). However, mutations on the Kelch-13 gene marking delayed parasite clearance have no clinically defined relationship with ACT resistance across Africa. With increasing malaria control efforts, declining acquired immunity could be responsible for varying drug response profiles that may be dependent on levels of exposure to infections. To examine antibody responses against malaria and the influence on the efficacy of artemether-lumefantrine (AL), plasma samples were collected, prior to treatment, from individuals presenting with uncomplicated malaria. Methods: Participants were stratified into two groups: early (within 24 hours, N = 20) and late (between 48 – 72 hours, N = 30) parasite clearance after treatment, as determined by var gene acidic terminal sequence (varATS) polymerase chain reaction. Magnetic bead-based luminex assay was used to profile antibody responses specific to a panel of 21 Plasmodium falciparum sporozoite, merozoite and An. gambiae salivary antigens. Results: Median fluorescence intensity (MFI) of the antibodies was highest against glutamate-rich protein (GLURP-R0) and lowest against merozoite surface protein (MSP2) antigen. Analysis showed a positive correlation between expression of immunity and age of individuals (P = 0.023). However, there was no association between parasite density and antibody responses, except a significant positive relationship with reticulocyte binding protein-like homologue 5 (Rh5), P = 0.047; Plasmodium exported protein (Hyp2), P = 0.037 and merozoite surface protein 11 (H103), P = 0.038. Though higher levels of antibodies against erythrocyte binding antigens (EBA 140 and 175), MSP1.19, GLURP, circumsporozoite protein (CSP) and Rh4.2 were observed in individuals who recorded early parasite clearance, there was no significant difference in antibody responses in the early and late parasitological response groups. Conclusions: Characterization of additional markers in larger populations is required to reveal potential immunological correlates of drug efficacy.

Immunization with AgTRIO, a Protein in Anopheles Saliva, Contributes to Protection against Plasmodium Infection in Mice

Plasmodium infection begins with the bite of an anopheline mosquito, when sporozoites along with saliva are injected into a vertebrate host. The role of the host responses to mosquito saliva components in malaria remains unclear. We observed that antisera against Anopheles gambiae salivary glands partially protected mice from mosquito-borne Plasmodium infection. Specifically, antibodies to A. gambiae TRIO (AgTRIO), a mosquito salivary gland antigen, contributed to the protection. Mice administered AgTRIO antiserum showed lower Plasmodium liver burden and decreased parasitemia when exposed to infected mosquitoes. Active immunization with AgTRIO was also partially protective against Plasmodium berghei infection. A combination of AgTRIO antiserum and antibodies against Plasmodium circumsporozoite protein, a vaccine candidate, further decreased P. berghei infection. In humanized mice, AgTRIO antiserum afforded some protection against mosquito-transmitted Plasmodium falciparum. AgTRIO antiserum reduced the movement of sporozoites in the murine dermis. AgTRIO may serve as an arthropod-based target against Plasmodium to combat malaria.

Mosquito-Borne Diseases and Omics: Salivary Gland Proteome of the Female Aedes aegypti Mosquito

The female Aedes aegypti mosquito is an important vector for several tropical and subtropical diseases such as dengue, chikungunya, and Zika and yellow fever. The disease viruses infect the mosquito and subsequently spread to the salivary glands after which the viruses can be transmitted to humans with probing or feeding by the mosquito. Omics systems sciences offer the opportunity to characterize vectors and can inform disease surveillance, vector control and development of innovative diagnostics, personalized medicines, vaccines, and insecticide targets. Using high-resolution mass spectrometry, we performed an analysis of the A. aegypti salivary gland proteome. The A. aegypti proteome resulted in acquisition of 83,836 spectra. Upon searches against the protein database of the A. aegypti, these spectra were assigned to 5417 unique peptides, belonging to 1208 proteins. To the best of our knowledge, this is the largest set of proteins identified in the A. aegypti salivary gland. Of note, 29 proteins were involved in immunity-related pathways in salivary glands. A subset of these proteins is known to interact with disease viruses. Another 15 proteins with signal cleavage site were found to be secretory in nature, and thus possibly playing critical roles in blood meal ingestion. These findings provide a baseline to advance our understanding of vector-borne diseases and vector-pathogen interactions before virus transmission in global health, and might therefore enable future design and development of virus-blocking strategies and novel molecular targets in the mosquito vector A. aegypti.

Serological measures to assess the efficacy of malaria control programme on Ambae Island, Vanuatu

Background

Seroepidemiology can provide evidence for temporal changes in malaria transmission and is an important tool to evaluate the effectiveness of control interventions. During the early 2000s, Vanuatu experienced an acute increase in malaria incidence due to a lapse in funding for vector control. After the distribution of subsidised insecticide-treated nets (ITNs) resumed in 2003, malaria incidence decreased in the subsequent years. This study was conducted to find the serological evidence supporting the impact of ITN on exposure to Anopheles vector bites and parasite prevalence.

Methods

On Ambae Island, blood samples were collected from 231 and 282 individuals in 2003 and 2007, respectively. Parasite prevalence was determined by microscopy. Antibodies to three Plasmodium falciparum (PfSE, PfMSP-1₁₉, and PfAMA-1) and three Plasmodium vivax (PvSE, PvMSP-1₁₉, and PvAMA-1) antigens, as well as the Anopheles-specific salivary antigen gSG6, were detected by ELISA. Age-specific seroprevalence was analysed using a reverse catalytic modelling approach to estimate seroconversion rates (SCRs).

Results

Parasite rate decreased significantly (P < 0.001) from 19.0% in 2003 to 3.2% in 2007, with a shift from P. falciparum predominance to P. falciparum-P. vivax co-dominance. Significant (P < 0.001) decreases were observed in seroprevalence to all three P. falciparum antigens but only two of three P. vivax antigens (except PvAMA-1; P = 0.153), consistent with the more pronounced decrease in P. falciparum prevalence. Seroprevalence to gSG6 also decreased significantly (P < 0.001), suggesting that reduced exposure to vector bites was important to the decrease in parasite prevalence between 2003 and 2007. Analyses of age-specific seroprevalence showed a three-fold decrease in P. falciparum transmission, but the evidence for the decrease in P. vivax transmission was less clear.

Conclusions

Serological markers pointed to the effectiveness of ITNs in reducing malaria prevalence on Ambae Island between 2003 and 2007. The recombinant gSG6 antigen originally developed to indicate exposure to the Afrotropical vector An. gambiae may be used in the Pacific to complement the traditional measure of entomological inoculation rate (EIR).

Anopheline salivary protein genes and gene families: an evolutionary overview after the whole genome sequence of sixteen Anopheles species

BACKGROUND

Mosquito saliva is a complex cocktail whose pharmacological properties play an essential role in blood feeding by counteracting host physiological response to tissue injury. Moreover, vector borne pathogens are transmitted to vertebrates and exposed to their immune system in the context of mosquito saliva which, in virtue of its immunomodulatory properties, can modify the local environment at the feeding site and eventually affect pathogen transmission. In addition, the host antibody response to salivary proteins may be used to assess human exposure to mosquito vectors. Even though the role of quite a few mosquito salivary proteins has been clarified in the last decade, we still completely ignore the physiological role of many of them as well as the extent of their involvement in the complex interactions taking place between the mosquito vectors, the pathogens they transmit and the vertebrate host. The recent release of the genomes of 16 Anopheles species offered the opportunity to get insights into function and evolution of salivary protein families in anopheline mosquitoes.

RESULTS

Orthologues of fifty three Anopheles gambiae salivary proteins were retrieved and annotated from 18 additional anopheline species belonging to the three subgenera Cellia, Anopheles, and Nyssorhynchus. Our analysis included 824 full-length salivary proteins from 24 different families and allowed the identification of 79 novel salivary genes and re-annotation of 379 wrong predictions. The comparative, structural and phylogenetic analyses yielded an unprecedented view of the anopheline salivary repertoires and of their evolution over 100 million years of anopheline radiation shedding light on mechanisms and evolutionary forces that contributed shaping the anopheline sialomes.

CONCLUSIONS

We provide here a comprehensive description, classification and evolutionary overview of the main anopheline salivary protein families and identify two novel candidate markers of human exposure to malaria vectors worldwide. This anopheline sialome catalogue, which is easily accessible as hyperlinked spreadsheet, is expected to be useful to the vector biology community and to improve the capacity to gain a deeper understanding of mosquito salivary proteins facilitating their possible exploitation for epidemiological and/or pathogen-vector-host interaction studies.

Use of an Anopheles Salivary Biomarker to Assess Malaria Transmission Risk Along the Thailand-Myanmar Border

Background

The modalities of malaria transmission along the Thailand-Myanmar border are poorly understood. Here we address the relevance of using a specific Anopheles salivary biomarker to measure the risk among humans of exposure to Anopheles bites.

Methods

Serologic surveys were conducted from May 2013 to December 2014 in 4 sentinel villages. More than 9400 blood specimens were collected in filter papers from all inhabitants at baseline and then every 3 months thereafter, for up to 18 months, for analysis by enzyme-linked immunosorbent assay. The relationship between the intensity of the human antibody response and entomological indicators of transmission (human biting rates and entomological inoculation rates [EIRs]) was studied using a multivariate 3-level mixed model analysis. Heat maps for human immunoglobulin G (IgG) responses for each village and survey time point were created using QGIS 2.4.

Results

The levels of IgG response among participants varied significantly according to village, season, and age (P<.001) and were positively associated with the abundance of total Anopheles species and primary malaria vectors and the EIR (P<.001). Spatial clusters of high-IgG responders were identified across space and time within study villages.

Conclusions

The gSG6-P1 biomarker has great potential to address the risk of transmission along the Thailand-Myanmar border and represents a promising tool to guide malaria interventions.

Human IgG Antibody Response to Aedes Nterm-34kDa Salivary Peptide, an Epidemiological Tool to Assess Vector Control in Chikungunya and Dengue Transmission Area

Background

Arboviral diseases are an important public health concerns. Vector control remains the sole strategy to fight against these diseases. Because of the important limits of methods currently used to assess human exposure to Aedes mosquito bites, much effort is being devoted to develop new indicators. Recent studies have reported that human antibody (Ab) responses to Aedes aegypti Nterm-34kDa salivary peptide represent a promising biomarker tool to evaluate the human-Aedes contact. The present study aims investigate whether such biomarker could be used for assessing the efficacy of vector control against Aedes.

Methodology/Principal findings

Specific human IgG response to the Nterm-34kDa peptide was assessed from 102 individuals living in urban area of Saint-Denis at La Reunion Island, Indian Ocean, before and after the implementation of vector control against Aedes mosquitoes. IgG response decreased after 2 weeks (P < 0.0001), and remained low for 4 weeks post-intervention (P = 0.0002). The specific IgG decrease was associated with the decline of Aedes mosquito density, as estimated by entomological parameters and closely correlated to vector control implementation and was not associated with the use of individual protection, daily commuting outside of the house, sex and age. Our findings indicate a probable short-term decrease of human exposure to Aedes bites just after vector control implementation.

Conclusion/Significance

Results provided in the present study indicate that IgG Ab response to Aedes aegypti Nterm-34kDa salivary peptide could be a relevant short-time indicator for evaluating the efficacy of vector control interventions against Aedes species.

In absence of effective treatment and vaccine, vector control is the main strategy against arboviral diseases such as dengue, Zika and chikungunya. Given the limitation of entomologic tool currently used, news tools are urgently needed to assess the efficacy of vector control against arboviral diseases. The present study aimed to investigate whether human IgG antibody specific response to only one Aedes salivary peptide could be useful for assessing the efficacy of vector control against arboviral diseases. For this purpose, IgG response to Nterm-34kDa peptide was assessed from 102 individuals living in urban area at La Reunion Island, Indian Ocean, before and after the implementation of vector control against Aedes albopictus mosquito species. A significant decrease of this specific IgG level was noticed after vector control implementation. The decrease was associated to the decline in Aedes mosquito density estimated by entomological parameters, such as adult mosquito density, House and Breteau indices. The results of the present study indicated that human IgG response to the Aedes Nterm-34kDa salivary peptide could be a useful tool to evaluate the efficacy of vector control strategies against arboviruses.

Identification of the secreted watery saliva proteins of the rice brown planthopper, Nilaparvata lugens (Stål) by transcriptome and Shotgun LC-MS/MS approach

The rice brown planthopper, Nilaparvata lugens (Stål), a major rice insect pest in Asia, is a vascular bundle-feeder that ejects gelling and watery saliva during the feeding process. Although major proteins in the salivary glands of N. lugens have been identified using 2D PAGE, very little is known about the secreted saliva of this insect. In this study, we identified the major proteins in the secreted watery saliva of N. lugens, via collecting from a sucrose diet that adult planthoppers had fed upon through a membrane of stretched parafilm, and using shotgun LC-MS/MS analysis with reference to transcriptome database of salivary glands of N. lugens. A total of 107 proteins were identified in the watery saliva of N. lugens, over 80% of which showed significant similarity to known proteins. When annotated by the Blast2GO suite, 29 proteins had catalytic activity and 24 proteins were binding proteins. The saliva enzymes included oxidoreductases, hydrolases, phosphatases, peptidases (proteases), kinases, transferases, and lyases. Binding proteins in N. lugens watery saliva included ATP-binding, lipophorin, calcium-binding, actin-binding and DNA-, RNA-, and chromatin-binding proteins. Other non-enzymatic proteins, such as ubiquitins, heat shock proteins, ribosomal proteins, and immunoglobulin proteins were also found in N. lugens watery saliva. This is the first study to identify, characterize and list the proteins in watery saliva of N. lugens, which might be involved in planthopper-rice interactions.

Detection of immunogenic proteins from Anopheles sundaicus salivary glands in the human serum

INTRODUCTION

The saliva of mosquitoes has an important role in the transmission of several diseases, including malaria, and contains substances with vasomodulating and immunomodulating effects to counteract the host physiological mechanisms and enhance pathogen transmission. As immunomodulatory components, salivary gland proteins can induce the generation of specific IgG antibodies in the host, which can be used as specific biomarkers of exposure to Anopheles sundaicus . The objective of this study was to identify immunogenic proteins from the salivary glands of Anopheles sundaicus by reaction with sera from individuals living in malaria-endemic areas who are thus exposed to Anopheles mosquitoes.

METHODS

IgG antibodies targeting salivary gland proteins in serum samples from individuals living in malaria-endemic areas were measured by enzyme-linked immunosorbent assay (ELISA). Sera from healthy individuals living in non-endemic areas were used as negative controls. Determination of the presence of salivary gland immunogenic proteins was carried out by western blotting.

RESULTS

Sixteen bands appeared in sodium dodecyl sulfate polyacrylamide gel electrophoresis, with molecule weights ranging from 22 to 144kDa. Among the exposed individuals, IgG responses to salivary gland proteins were variable. Protein bands with molecular weights of 46, 41, 33, and 31kDa were the most immunogenic. These immunogenic proteins were consistently recognized by pooled serum and individual samples from people living in malaria-endemic areas but not by negative controls.

CONCLUSIONS

These results support the potential use of immunogenic proteins from the salivary glands of Anopheles as candidate markers of bite exposure or in malaria vaccines.

Salivary Biomarkers in the Control of Mosquito-Borne Diseases

Vector control remains the most effective measure to prevent the transmission of mosquito-borne diseases. However, the classical entomo-parasitological methods used to evaluate the human exposure to mosquito bites and the effectiveness of control strategies are indirect, labor intensive, and lack sensitivity in low exposure/transmission areas. Therefore, they are limited in their accuracy and widespread use. Studying the human antibody response against the mosquito salivary proteins has provided new biomarkers for a direct and accurate evaluation of the human exposure to mosquito bites, at community and individual levels. In this review, we discuss the development, applications and limits of these biomarkers applied to Aedes- and Anopheles-borne diseases.

Immunogenicity and Serological Cross-Reactivity of Saliva Proteins among Different Tsetse Species

Tsetse are vectors of pathogenic trypanosomes, agents of human and animal trypanosomiasis in Africa. Components of tsetse saliva (sialome) are introduced into the mammalian host bite site during the blood feeding process and are important for tsetse’s ability to feed efficiently, but can also influence disease transmission and serve as biomarkers for host exposure. We compared the sialome components from four tsetse species in two subgenera: subgenus Morsitans: Glossina morsitans morsitans (Gmm) and Glossina pallidipes (Gpd), and subgenus Palpalis: Glossina palpalis gambiensis (Gpg) and Glossina fuscipes fuscipes (Gff), and evaluated their immunogenicity and serological cross reactivity by an immunoblot approach utilizing antibodies from experimental mice challenged with uninfected flies. The protein and immune profiles of sialome components varied with fly species in the same subgenus displaying greater similarity and cross reactivity. Sera obtained from cattle from disease endemic areas of Africa displayed an immunogenicity profile reflective of tsetse species distribution. We analyzed the sialome fractions of Gmm by LC-MS/MS, and identified TAg5, Tsal1/Tsal2, and Sgp3 as major immunogenic proteins, and the 5'-nucleotidase family as well as four members of the Adenosine Deaminase Growth Factor (ADGF) family as the major non-immunogenic proteins. Within the ADGF family, we identified four closely related proteins (TSGF-1, TSGF-2, ADGF-3 and ADGF-4), all of which are expressed in tsetse salivary glands. We describe the tsetse species-specific expression profiles and genomic localization of these proteins. Using a passive-immunity approach, we evaluated the effects of rec-TSGF (TSGF-1 and TSGF-2) polyclonal antibodies on tsetse fitness parameters. Limited exposure of tsetse to mice with circulating anti-TSGF antibodies resulted in a slight detriment to their blood feeding ability as reflected by compromised digestion, lower weight gain and less total lipid reserves although these results were not statistically significant. Long-term exposure studies of tsetse flies to antibodies corresponding to the ADGF family of proteins are warranted to evaluate the role of this conserved family in fly biology.

Insect saliva contains many proteins that are injected into the mammalian host during the blood feeding process. Saliva proteins enhance the blood feeding ability of insects, but they can also induce mammalian immune responses that inhibit successful feeding, or modulate the bite site to benefit pathogen transmission. Here we studied saliva from four different tsetse species that belong to two distant species groups. We show that the saliva protein profiles of different species groups vary. Experimental mice subjected to fly bites display varying immunological responses against the abundant saliva proteins and the antigenicity of the shared saliva proteins in different tsetse species differs. We show that one member of the ADGF family with adenosine deaminase motifs, TSGF-2, is non-immunogenic in Glossina morsitans in mice, while the same protein from Glossina fuscipes is highly immunogenic. Such species-specific immune responses could be exploited as biomarkers of host exposures in the field. We also show that short-term exposure of G. morsitans to mice passively immunized by anti-TSGF antibodies leads to slight but not statistically significant negative fitness effects. Thus, future investigations with non-antigenic saliva proteins are warranted as they can lead to novel mammalian vaccine targets to reduce tsetse populations in the field.

Specific antibodies to Anopheles gSG6-P1 salivary peptide to assess early childhood exposure to malaria vector bites

Background

The estimates of risk of malaria in early childhood are imprecise given the current entomologic and parasitological tools. Thus, the utility of anti-Anopheles salivary gSG6-P1 peptide antibody responses in measuring exposure to Anopheles bites during early infancy has been assessed.

Methods

Anti-gSG6-P1 IgG and IgM levels were evaluated in 133 infants (in Benin) at three (M3), six (M6), nine (M9) and 12 (M12) months of age. Specific IgG levels were also assessed in their respective umbilical cord blood (IUCB) and maternal blood (MPB).

Results

At M3, 93.98 and 41.35% of infants had anti-gSG6-P1 IgG and IgM Ab, respectively. Specific median IgG and IgM levels gradually increased between M3 and M6 (p < 0.0001 and p < 0.001), M6–M9 (p < 0.0001 and p = 0.085) and M9–M12 (p = 0.002 and p = 0.03). These levels were positively associated with the Plasmodium falciparum infection intensity (p = 0.006 and 0.003), and inversely with the use of insecticide-treated bed nets (p = 0.003 and 0.3). Levels of specific IgG in the MPB were positively correlated to those in the IUCB (R = 0.73; p < 0.0001) and those at M3 (R = 0.34; p < 0.0001).

Conclusion

The exposure level to Anopheles bites, and then the risk of malaria infection, can be evaluated in young infants by assessing anti-gSG6-P1 IgM and IgG responses before and after 6-months of age, respectively. This tool can be useful in epidemiological evaluation and surveillance of malaria risk during the first year of life.

Vector-transmitted disease vaccines: targeting salivary proteins in transmission (SPIT)

More than half the population of the world is at risk for morbidity and mortality from vector-transmitted diseases, and emerging vector-transmitted infections are threatening new populations. Rising insecticide resistance and lack of efficacious vaccines highlight the need for novel control measures. One such approach is targeting the vector-host interface by incorporating vector salivary proteins in anti-pathogen vaccines. Debate remains about whether vector saliva exposure exacerbates or protects against more severe clinical manifestations, induces immunity through natural exposure or extends to all vector species and associated pathogens. Nevertheless, exploiting this unique biology holds promise as a viable strategy for the development of vaccines against vector-transmitted diseases.

Serological evidence of vector and parasite exposure in Southern Ghana: the dynamics of malaria transmission intensity

BACKGROUND

Seroepidemiology provides robust estimates for tracking malaria transmission when intensity is low and useful when there is no baseline entomological data. Serological evidence of exposure to malaria vectors and parasite contribute to our understanding of the risk of pathogen transmission, and facilitates implementation of targeted interventions. Ab to Anopheles gambiae salivary peptide (gSG6-P1) and merozoite surface protein one (MSP-1(19)) reflect human exposure to malaria vectors and parasites. This study estimated malaria transmission dynamics using serological evidence of vector and parasite exposure in southern Ghana.

METHODS

Total IgG responses to both antigens in an age stratified cohort (<5, 5-14, >14) were measured from South-eastern Ghana. 295 randomly selected sera were analyzed from archived samples belonging to a cohort study that were followed at 3 consecutive survey months (n = 885); February, May and August 2009. Temporal variations in seroprevalence of both antigens as well as differences between the age-stratified cohorts were determined by χ (2) test with p < 0.05 statistically significant. Non-parametric repeated ANOVA - Friedman's test was used to test differences in antibody levels. Seroprevalence data were fitted to reversible catalytic model to estimate sero-conversion rates.

RESULTS

Whereas parasite prevalence was generally low 2.4%, 2.7% and 2.4% with no apparent trends with season, seroprevalence to both gSG6-P1 and MSP1(19) were high (59%, 50.9%, 52.2%) and 57.6%, 52.3% and 43.6% in respective order from Feb. to August. Repeated measures ANOVA showed differences in median antibody levels across surveys with specific significant differences between February and May but not August by post hoc Dunn's multiple comparison tests for gSG6-P1. For MSP1(19), no differences were observed in antibody levels between February and May but a significant decline was observed from May to August. Seroconversion rates for gSG6-P1 increased by 1.5 folds from February to August and 3 folds for MSP1(19).

CONCLUSION

Data suggests exposure to infectious bites may be declining whereas mosquito bites remains high. Sustained malaria control efforts and surveillance are needed to drive malaria further down and to prevent catastrophic rebound. Operational factors for scaling up have been discussed.

The Anopheles gambiae cE5 salivary protein: a sensitive biomarker to evaluate the efficacy of insecticide-treated nets in malaria vector control

Evaluation of vector control is crucial for improving malaria containment and, according to World Health Organization, new complementary indicators would be very valuable. In this study the IgG response to the Anopheles-specific cE5 salivary protein was tested as a tool to evaluate the efficacy of insecticide-treated nets in reducing human exposure to malaria vectors. Sera collected during a longitudinal study carried out in Angola, and including entomological and parasitological data, were used to assess the IgG response to the Anopheles gambiae cE5 in both children and adults, before and after the application of insecticide-treated nets. Seasonal fluctuation of specific IgG antibody levels according to exposure was only found in children (up to ≈ 14 years old) whose anti-cE5 IgG response dropped after bed nets installation. These results were fully consistent with previous findings obtained with the same set of sera and indicating a substantial reduction of human-vector contact shortly after nets implementation. Overall, children IgG response to the cE5 protein appeared a very sensitive biomarker, which allowed for the detection of even weak exposure to Anopheles bites, indicating it may represent a reliable additional tool to evaluate the efficacy of vector control interventions.

Anopheles gambiae salivary protein expression modulated by wild Plasmodium falciparum infection: highlighting of new antigenic peptides as candidates of An. gambiae bites

Background

Malaria is the major parasitic disease worldwide caused by Plasmodium infection. The objective of integrated malaria control programs is to decrease malaria transmission, which needs specific tools to be accurately assessed. In areas where the transmission is low or has been substantially reduced, new complementary tools have to be developed to improve surveillance. A recent approach, based on the human antibody response to Anopheles salivary proteins, has been shown to be efficient in evaluating human exposure to Anopheles bites. The aim of the present study was to identify new An. gambiae salivary proteins as potential candidate biomarkers of human exposure to P. falciparum-infective bites.

Methods

Experimental infections of An. gambiae by wild P. falciparum were carried out in semi-field conditions. Then a proteomic approach, combining 2D-DIGE and mass spectrometry, was used to identify the overexpressed salivary proteins in infected salivary glands compared to uninfected An. gambiae controls. Subsequently, a peptide design of each potential candidate was performed in silico and their antigenicity was tested by an epitope-mapping technique using blood from individuals exposed to Anopheles bites.

Results

Five salivary proteins (gSG6, gSG1b, TRIO, SG5 and long form D7) were overexpressed in the infected salivary glands. Eighteen peptides were designed from these proteins and were found antigenic in children exposed to the Anopheles bites. Moreover, the results showed that the presence of wild P. falciparum in salivary glands modulates the expression of several salivary proteins and also appeared to induce post-translational modifications.

Conclusions

This study is, to our knowledge, the first that compares the sialome of An. gambiae both infected and not infected by wild P. falciparum, making it possible to mimic the natural conditions of infection. This is a first step toward a better understanding of the close interactions between the parasite and the salivary gland of mosquitoes. In addition, these results open the way to define biomarkers of infective bites of Anopheles, which could, in the future, improve the estimation of malaria transmission and the evaluation of malaria vector control tools.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-014-0599-y) contains supplementary material, which is available to authorized users.

Monitoring human tick-borne disease risk and tick bite exposure in Europe: available tools and promising future methods

Ticks are the main vector for infectious disease pathogens in both humans and animals, and tick-borne diseases are currently spreading throughout Europe. Various surveillance methods have been developed to estimate the burden and risk of tick-borne diseases and host exposure to tick bites. The ultimate aims of these approaches are to determine the risk level of a tick-borne disease in a given area, determine its health priority, identify the at-risk population and propose specific countermeasures or complementary studies as needed. The purpose of this review is to present the current methods for monitoring the circulation of tick-borne diseases and to highlight the use of salivary antigens as original and recently developed serological tools that could be useful for tick bite risk assessment and could improve the current surveillance methods.