Zika vector competence data reveals risks of outbreaks: the contribution of the European ZIKAlliance project

First identified in 1947, Zika virus took roughly 70 years to cause a pandemic unusually associated with virus-induced brain damage in newborns. Zika virus is transmitted by mosquitoes, mainly Aedes aegypti, and secondarily, Aedes albopictus, both colonizing a large strip encompassing tropical and temperate regions. As part of the international project ZIKAlliance initiated in 2016, 50 mosquito populations from six species collected in 12 countries were experimentally infected with different Zika viruses. Here, we show that Ae. aegypti is mainly responsible for Zika virus transmission having the highest susceptibility to viral infections. Other species play a secondary role in transmission while Culex mosquitoes are largely non-susceptible. Zika strain is expected to significantly modulate transmission efficiency with African strains being more likely to cause an outbreak. As the distribution of Ae. aegypti will doubtless expand with climate change and without new marketed vaccines, all the ingredients are in place to relive a new pandemic of Zika.info:eu-repo/semantics/publishedVersio

Zika vector competence data reveals risks of outbreaks: the contribution of the European ZIKAlliance project

First identified in 1947, Zika virus took roughly 70 years to cause a pandemic unusually associated with virus-induced brain damage in newborns. Zika virus is transmitted by mosquitoes, mainly Aedes aegypti, and secondarily, Aedes albopictus, both colonizing a large strip encompassing tropical and temperate regions. As part of the international project ZIKAlliance initiated in 2016, 50 mosquito populations from six species collected in 12 countries were experimentally infected with different Zika viruses. Here, we show that Ae. aegypti is mainly responsible for Zika virus transmission having the highest susceptibility to viral infections. Other species play a secondary role in transmission while Culex mosquitoes are largely non-susceptible. Zika strain is expected to significantly modulate transmission efficiency with African strains being more likely to cause an outbreak. As the distribution of Ae. aegypti will doubtless expand with climate change and without new marketed vaccines, all the ingredients are in place to relive a new pandemic of Zika

Cytoplasmic Incompatibility as a Means of Controlling Culex pipiens quinquefasciatus Mosquito in the Islands of the South-Western Indian Ocean

The use of the bacterium Wolbachia is an attractive alternative method to control vector populations. In mosquitoes, as in members of the Culex pipiens complex, Wolbachia induces a form of embryonic lethality called cytoplasmic incompatibility, a sperm-egg incompatibility occurring when infected males mate either with uninfected females or with females infected with incompatible Wolbachia strain(s). Here we explore the feasibility of the Incompatible Insect Technique (IIT), a species-specific control approach in which field females are sterilized by inundative releases of incompatible males. We show that the Wolbachia wPip(Is) strain, naturally infecting Cx. p. pipiens mosquitoes from Turkey, is a good candidate to control Cx. p. quinquefasciatus populations on four islands of the south-western Indian Ocean (La Réunion, Mauritius, Grande Glorieuse and Mayotte). The wPip(Is) strain was introduced into the nuclear background of Cx. p. quinquefasciatus mosquitoes from La Réunion, leading to the LR[wPip(Is)] line. Total embryonic lethality was observed in crosses between LR[wPip(Is)] males and all tested field females from the four islands. Interestingly, most crosses involving LR[wPip(Is)] females and field males were also incompatible, which is expected to reduce the impact of any accidental release of LR[wPip(Is)] females. Cage experiments demonstrate that LR[wPip(Is)] males are equally competitive with La Réunion males resulting in demographic crash when LR[wPip(Is)] males were introduced into La Réunion laboratory cages. These results, together with the geographic isolation of the four south-western Indian Ocean islands and their limited land area, support the feasibility of an IIT program using LR[wPip(Is)] males and stimulate the implementation of field tests for a Cx. p. quinquefasciatus control strategy on these islands

Transcriptomic analysis of insecticide resistance in the lymphatic filariasis vector Culex quinquefasciatus

Culex quinquefasciatus plays an important role in transmission of vector-borne diseases of public health importance, including lymphatic filariasis (LF), as well as many arboviral diseases. Currently, efforts to tackle C. quinquefasciatus vectored diseases are based on either mass drug administration (MDA) for LF, or insecticide-based interventions. Widespread and intensive insecticide usage has resulted in increased resistance in mosquito vectors, including C. quinquefasciatus. Herein, the transcriptome profile of Ugandan bendiocarb-resistant C. quinquefasciatus was explored to identify candidate genes associated with insecticide resistance. High levels of insecticide resistance were observed for five out of six insecticides tested, with the lowest mortality (0.97%) reported to permethrin, while for DDT, lambdacyhalothrin, bendiocarb and deltamethrin the mortality rate ranged from 1.63–3.29%. Resistance to bendiocarb in exposed mosquitoes was marked, with 2.04% mortality following 1 h exposure and 58.02% after 4 h. Genotyping of the G119S Ace-1 target site mutation detected a highly significant association (p 8-fold increase vs unexposed controls). These results provide evidence that bendiocarb resistance in Ugandan C. quinquefasciatus is mediated by both target-site mechanisms and over-expression of detoxification enzymes

Insecticide resistance in Culicidae vectors in insular territories

La résistance aux insecticides est un phénomène naturel d'adaptation des insectes. Lorsqu'elle apparaît dans une population de vecteur, elle compromet les interventions de lutte anti-vectorielle, et limite les possibilités de contrôle des agents pathogènes qu'ils transmettent. La résistance aux insecticides chez les Culicidae vecteurs est largement répandue de par le monde, et on la retrouve notamment dans les territoires insulaires. Cependant, l'isolement géographique des îles influe sur la présence et la distribution des allèles de résistance. En travaillant sur quatre espèces de moustiques dans plusieurs contextes insulaires, nous nous sommes attachés à (i) évaluer les niveaux de résistance et à caractériser les mécanismes impliqués, (ii) identifier les facteurs, contextuels et/ou évolutifs, expliquant la présence et la distribution des gènes de résistance chez certaines de ces espèces, et (iii) évaluer de nouveaux outils de lutte pouvant être mis en place dans le contexte insulaire particulier que représente Mayotte. Nos résultats montrent une forte résistance de Culex p. quinquefasciatus à toutes les familles d'insecticides utilisées jusqu'à présent dans l'Océan Indien. Cependant, la distribution de ces mécanismes de résistance a présenté une forte hétérogénéité régionale, les allèles de résistance n'étant pas présents dans toutes les îles et/ou pas aux mêmes fréquences. De plus, à une échelle plus locale sur l'île de Mayotte, il existe de fortes disparités entre les espèces étudiées en terme de résistance. Ces différences inter-espèces, intra-île et inter-îles sont discutées en fonction de l'influence des pressions de sélections locales et de leurs sources, et du coût génétique des différents allèles présents. Des propositions d'évolution des pratiques de lutte à Mayotte sont énoncées, intégrant les nouveaux outils que nous avons évalués sur le terrain.Insecticide resistance is a natural adaptation phenomenon of insects. When it occurs in a vector population, it compromises vector control interventions, and therefore limits the ability to control the diseases they transmit. Insecticide resistance in Culicidae is widespread throughout the world, and is also found in islands. However, their geographic isolation influences the presence and distribution of resistance alleles. We have worked on four mosquito species in several islands, and we tried to (i) assess the resistance levels and characterize the mechanisms involved, (ii) identify contextual and/or evolutionary factors explaining the presence and distribution of resistance genes in some of these species, and (iii) evaluate new control tools that can be implemented in the specific context of Mayotte island. Our results showed a strong resistance of Culex p. quinquefasciatus to all insecticide families used so far in the Indian Ocean. However, the distribution of resistance mechanisms showed a strong spatial heterogeneity. Indeed, some resistance alleles were not present on all islands and/or not at the same frequencies. In addition, at a more local scale in Mayotte, there were strong differences of resistance status between species. These differences between species and islands are discussed in relation to the influence of local selection pressures and their origins, and to the fitness cost of different alleles. Proposals for modification in vector control practices are set to Mayotte, integrating new tools we have evaluated on the field

Insecticide resistance in Culicidae vectors in insular territories

La résistance aux insecticides est un phénomène naturel d'adaptation des insectes. Lorsqu'elle apparaît dans une population de vecteur, elle compromet les interventions de lutte anti-vectorielle, et limite les possibilités de contrôle des agents pathogènes qu'ils transmettent. La résistance aux insecticides chez les Culicidae vecteurs est largement répandue de par le monde, et on la retrouve notamment dans les territoires insulaires. Cependant, l'isolement géographique des îles influe sur la présence et la distribution des allèles de résistance. En travaillant sur quatre espèces de moustiques dans plusieurs contextes insulaires, nous nous sommes attachés à (i) évaluer les niveaux de résistance et à caractériser les mécanismes impliqués, (ii) identifier les facteurs, contextuels et/ou évolutifs, expliquant la présence et la distribution des gènes de résistance chez certaines de ces espèces, et (iii) évaluer de nouveaux outils de lutte pouvant être mis en place dans le contexte insulaire particulier que représente Mayotte. Nos résultats montrent une forte résistance de Culex p. quinquefasciatus à toutes les familles d'insecticides utilisées jusqu'à présent dans l'Océan Indien. Cependant, la distribution de ces mécanismes de résistance a présenté une forte hétérogénéité régionale, les allèles de résistance n'étant pas présents dans toutes les îles et/ou pas aux mêmes fréquences. De plus, à une échelle plus locale sur l'île de Mayotte, il existe de fortes disparités entre les espèces étudiées en terme de résistance. Ces différences inter-espèces, intra-île et inter-îles sont discutées en fonction de l'influence des pressions de sélections locales et de leurs sources, et du coût génétique des différents allèles présents. Des propositions d'évolution des pratiques de lutte à Mayotte sont énoncées, intégrant les nouveaux outils que nous avons évalués sur le terrain.Insecticide resistance is a natural adaptation phenomenon of insects. When it occurs in a vector population, it compromises vector control interventions, and therefore limits the ability to control the diseases they transmit. Insecticide resistance in Culicidae is widespread throughout the world, and is also found in islands. However, their geographic isolation influences the presence and distribution of resistance alleles. We have worked on four mosquito species in several islands, and we tried to (i) assess the resistance levels and characterize the mechanisms involved, (ii) identify contextual and/or evolutionary factors explaining the presence and distribution of resistance genes in some of these species, and (iii) evaluate new control tools that can be implemented in the specific context of Mayotte island. Our results showed a strong resistance of Culex p. quinquefasciatus to all insecticide families used so far in the Indian Ocean. However, the distribution of resistance mechanisms showed a strong spatial heterogeneity. Indeed, some resistance alleles were not present on all islands and/or not at the same frequencies. In addition, at a more local scale in Mayotte, there were strong differences of resistance status between species. These differences between species and islands are discussed in relation to the influence of local selection pressures and their origins, and to the fitness cost of different alleles. Proposals for modification in vector control practices are set to Mayotte, integrating new tools we have evaluated on the field

BioRssay : an R package for analyses of bioassays and probit graphs

Dose-response relationships reflect the effects of a substance on organisms, and are widely used in broad research areas, from medicine and physiology, to vector control and pest management in agronomy. Furthermore, reporting on the response of organisms to stressors is an essential component of many public policies (e.g. public health, environment), and assessment of xenobiotic responses is an integral part of World Health Organization recommendations. Building upon an R script that we previously made available, and considering its popularity, we have now developed a software package in the R environment, BioRssay, to efficiently analyze dose-response relationships. It has more user-friendly functions and more flexibility, and proposes an easy interpretation of the results. The functions in the BioRssay package are built on robust statistical analyses to compare the dose/exposure-response of various bioassays and effectively visualize them in probit-graphs

Vector competence of Aedes aegypti from New Caledonia for the four recent circulating dengue virus serotypes

International audienceIn New Caledonia (NC), Aedes aegypti is the only proven vector of dengue virus (DENV), which is the most prevalent arbovirosis in NC. Since World War II, the four DENV serotypes have circulated regularly in NC. The epidemiological profile, however, has evolved over the last ten years, with the persistence of DENV-1 circulation and the co-circulation of several DENV serotypes. The current study evaluated the ability of Ae. aegypti from NC to transmit four DENV serotypes (and two DENV-1 genotypes) isolated during recent outbreaks in NC. An Ae. aegypti F1 generation was twice independently orally challenged with each DENV strain (107 FFU/ml). Infection, dissemination and transmission rates and transmission efficiency were measured at day 7 and 14 post-exposure, as well as the quantity of infectious virus particles. Mosquito infection was observed as early as 7 days post-infection. Infection rates between 18 and 58% were measured for all DENV serotypes/genotypes tested. Although dissemination rates ranged from 78 to 100%, transmission efficiencies were low, with values not exceeding 21% at 14 days post-infection for all DENV strains. This study shows that NC Ae. aegypti are moderately competent for DENV in laboratory conditions. In link with epidemiological data, these results suggest implication of other factors in the sustained circulation of DENV-1 in New Caledonia

Introduction of the Anopheles bancroftii Mosquito, a Malaria Vector, into New Caledonia

International audienceIn June 2017, an Anopheles mosquito species was detected in New Caledonia. Morphologic identification and genomic sequencing revealed that the specimens tested belong to An. bancroftii genotype A1. This introduction underscores the risk for local malaria transmission and the vulnerability of New Caledonia to vector introduction

Insecticide resistance in disease vectors from Mayotte : an opportunity for integrated vector management

Background: Mayotte, a small island in the Indian Ocean, has been affected for many years by vector-borne diseases. Malaria, Bancroftian filariasis, dengue, chikungunya and Rift Valley fever have circulated or still circulate on the island. They are all transmitted by Culicidae mosquitoes. To limit the impact of these diseases on human health, vector control has been implemented for more than 60 years on Mayotte. In this study, we assessed the resistance levels of four major vector species (Anopheles gambiae, Culex pipiens quinquefasciatus, Aedes aegypti and Aedes albopictus) to two types of insecticides: i) the locally currently-used insecticides (organophosphates, pyrethroids) and ii) alternative molecules that are promising for vector control and come from different insecticide families (bacterial toxins or insect growth regulators). When some resistance was found to one of these insecticides, we characterized the mechanisms involved. Methods: Larval and adult bioassays were used to evaluate the level of resistance. When resistance was found, we tested for the presence of metabolic resistance through detoxifying enzyme activity assays, or for target-site mutations through molecular identification of known resistance alleles. Results: Resistance to currently-used insecticides varied greatly between the four vector species. While no resistance to any insecticides was found in the two Aedes species, bioassays confirmed multiple resistance in Cx. p. quinquefasciatus (temephos: similar to 20 fold and deltamethrin: only 10% mortality after 24 hours). In An. gambiae, resistance was scarce: only a moderate resistance to temephos was found (similar to 5 fold). This resistance appears to be due only to carboxyl-esterase overexpression and not to target modification. Finally, and comfortingly, none of the four species showed resistance to any of the new insecticides. Conclusions: The low resistance observed in Mayotte's main disease vectors is particularly interesting, because it leaves a range of tools useable by vector control services. Together with the relative isolation of the island (thus limited immigration of mosquitoes), it provides us with a unique place to implement an integrated vector management plan, including all the good practices learned from previous experiences