Marie Vazeille

Wolbachia -based interventions have become a successful biological strategy to reduce dengue virus (DENV) transmission by Aedes aegypti . However, whether the protective phenotypes conferred by this symbiont remain stable under environmental stress remains poorly understood. Here, we investigated the impact of sublethal insecticide (deltamethrin) exposure on multiple components of the Wolbachia – Aedes aegypti –DENV system, including pathogen blocking, cytoplasmic incompatibility, host reproductive traits, symbiont density, and viral diversity. We show that insecticide exposure induces a transient reduction in Wolbachia density, which rapidly recovers without compromising DENV blocking, cytoplasmic incompatibility, or reproductive performance. In addition, insecticide exposure has a negligible impact on viral genetic diversity in mosquito saliva. These findings demonstrate the robustness of Wolbachia -mediated pathogen blocking under chemical stress and provide evidence that symbiont-based biological control can remain effective under environmentally challenging conditions.

In 2016, 11 travelers infected with yellow fever virus (YFV) were diagnosed in China after returning from Angola. These reported cases outside yellow fever (YF) endemic regions in Africa and South America did not trigger local transmission in this country where ~ 2 billion immunologically naïve people for YF cohabit with YFV-competent Aedes aegypti mosquitoes. We hypothesize that orthoflaviviruses endemic to Asia such as dengue virus (DENV) and Japanese encephalitis virus (JEV) might limit YFV transmission by local Ae. aegypti . Here, we show that YFV transmission by mosquitoes was inhibited after a primo-infection with DENV or JEV. DENV- or JEV-derived small RNAs did not target YFV genome but some mosquito antiviral genes belonging to the siRNA and IMD pathways were differentially expressed following primo-infection. In a context of growing co-circulation of multiple arboviruses, a better understanding of transmission dynamics by vectors is critical to predict emergence and improve preparedness against future pandemics.

Emerging arboviruses of the Orthoflavivirus genus such as West Nile virus (WNV) and Usutu virus (USUV), primarily transmitted by Culex mosquitoes, pose significant public health threats due to their ability to cause severe neurological diseases in humans and animals. While studies in North America and Central Europe have shown that these viruses can persist in overwintering mosquitoes, their role in viral maintenance during the cold season in northeastern France remains unknown. This study aimed to assess whether overwintering female mosquitoes in this region could harbor WNV or USUV during the cold season, potentially maintaining viral circulation until the following transmission season. Between October 2021 and February 2024, a total of 10,617 overwintering female mosquitoes were collected in various types of habitats across five departments in northeastern France. The most common species was Culex pipiens (88%). Mosquitoes were grouped into 1121 pools (1–10 individuals each) and tested by real-time RT-PCR for WNV, USUV, and other flaviviruses using a pan-Flavivirus NS5-targeting assay. All pools tested negative, indicating no evidence of viral RNA in overwintering females. These results suggested that overwintering female mosquitoes in northeastern France do not act as reservoirs for WNV or USUV, and do not contribute to their overwintering maintenance.

Emerging arboviruses of Orthoflavivirus genus such as West Nile virus (WNV) and Usutu virus (USUV), primarily transmitted by Culex mosquitoes, pose significant public health threats due to their ability to cause severe neurological diseases in humans and animals. While studies in North America and Central Europe have shown that these viruses can persist in overwintering mosquitoes, their role in viral maintenance during the cold season in northeastern France remains unknown. This study aimed to assess whether overwintering female mosquitoes in this region could harbor WNV or USUV during the cold season, potentially maintaining viral circulation until the following transmission season. Between October 2021 and February 2024, a total of 10,617 overwintering female mosquitoes were collected in various types of habitats, across five departments in northeastern France. The most common species was Culex pipiens (88%). Mosquitoes were grouped into 1,121 pools (1–10 individuals each) and tested by real-time RT-PCR for WNV, USUV, and other flaviviruses using a pan-Flavivirus NS5-targeting assay. All pools tested negative, indicating no evidence of viral RNA in overwintering females. These results suggest that overwintering female mosquitoes in northeastern France do not act as reservoirs for WNV or USUV, and do not contribute to their overwintering maintenance.

The mosquito-borne disease, Yellow fever (YF), has been largely controlled via mass delivery of an effective vaccine and mosquito control interventions. However, there are warning signs that YF is re-emerging in both Sub-Saharan Africa and South America. Imported from Africa in slave ships, YF was responsible for devastating outbreaks in the Caribbean. In Martinique, the last YF outbreak was reported in 1908 and the mosquito Aedes aegypti was incriminated as the main vector. We evaluated the vector competence of fifteen Ae. aegypti populations for five YFV genotypes (Bolivia, Ghana, Nigeria, Sudan, and Uganda). Here we show that mosquito populations from the Caribbean and the Americas were able to transmit the five YFV genotypes, with YFV strains for Uganda and Bolivia having higher transmission success. We also observed that Ae. aegypti populations from Martinique were more susceptible to YFV infection than other populations from neighboring Caribbean islands, as well as North and South America. Our vector competence data suggest that the threat of re-emergence of YF in Martinique and the subsequent spread to Caribbean nations and beyond is plausible.

Mosquito-borne diseases are spreading globally due to the expansion of the geographic range of competent mosquito vector species and increased human movement, especially infected travelers from endemic to non-endemic regions. Yellow fever (YF) has been largely controlled via mass delivery of an effective vaccine and mosquito control interventions. However, there are warning signs that YF is re-emerging in both Sub-Saharan Africa and South America. Imported from Africa to the Americas in slave ships, YF was responsible for devastating urban outbreaks for several centuries. In the Caribbean, the last YF outbreak was reported in 1908 in Martinique. The mosquito Aedes aegypti is the main vector for urban transmission in YF-endemic regions. However, it is unclear if all Ae. aegypti populations can effectively vector yellow fever virus (YFV), as there is growing evidence that intrinsic virus and mosquito host factors can significantly influence arbovirus transmission. We evaluated the vector competence of fifteen Ae. aegypti populations (nine from Martinique, two from Haiti, one from Guadeloupe, one from Cuba, one from Florida (USA), and one from Colombia) for five YFV genotypes (Bolivia, Ghana, Nigeria, Sudan, and Uganda) at 14 and 21 days post-infectious feeding. Mosquito populations from the Caribbean and the Americas were able to transmit the five YFV genotypes, in some cases achieving viral loads in mosquito saliva of up to several thousands of infectious virus particles, with YFV strains for Uganda and Bolivia having higher transmission success. We also observed that Ae. aegypti populations from Martinique were more susceptible to YFV infection than other populations from neighboring Caribbean islands, as well as North and South America. Our vector competence data suggest that the threat of re-emergence of YF in Martinique and the subsequent spread to Caribbean nations and beyond is plausible.

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.

In most of the world, Dengue virus (DENV) is mainly transmitted by the mosquito Aedes aegypti while in Europe, Aedes albopictus is responsible for human DENV cases since 2010. Identifying mutations that make DENV more competent for transmission by Ae. albopictus will help to predict emergence of epidemic strains. Ten serial passages in vivo in Ae. albopictus led to select DENV-1 strains with greater infectivity for this vector in vivo and in cultured mosquito cells. These changes were mediated by multiple adaptive mutations in the virus genome, including a mutation at position 10,418 in the DENV 3’UTR within an RNA stem-loop structure involved in subgenomic flavivirus RNA (sfRNA) production. Using reverse genetics, we showed that the 10,418 mutation alone does not confer a detectable increase in transmission efficiency in vivo . These results reveal the complex adaptive landscape of DENV transmission by mosquitoes and emphasize the role of epistasis in shaping evolutionary trajectories of DENV variants.

Vector competence is an important parameter in evaluating whether a species plays a role in transmission of an arbovirus. Although the protocols are similar, interpretation of results is unique given the specific interactions that exist between a mosquito population and a viral genotype. Here, we assessed the infection (IR), dissemination (DR), and transmission (TR) rates of Cx. pipiens s.l., collected from Iran, for West Nile virus (WNV) lineage 1a. We showed that Cx. pipiens s.l. mosquitoes in Iran were susceptible to WNV with IR up to 89.7%, 93.6%, and 83.9% at 7, 14, and 21 days post-infection (dpi) respectively. In addition, DR and TR reached respectively 92.3% and 75.0% at 21 dpi, and the number of viral particles delivered with saliva reached up to 1.33 × 10⁵ particles. Therefore, an unexpected high risk of WNV dissemination in the region where Cx. pipiens s.l. mosquitoes are well established should be considered carefully and surveillance measures implemented accordingly.

Mosquitoes are vectors of arboviruses affecting animal and human health. Arboviruses circulate primarily within an enzootic cycle and recurrent spillovers contribute to the emergence of human-adapted viruses able to initiate an urban cycle involving anthropophilic mosquitoes. The increasing volume of travel and trade offers multiple opportunities for arbovirus introduction in new regions. This scenario has been exemplified recently with the Zika pandemic. To incriminate a mosquito as vector of a pathogen, several criteria are required such as the detection of natural infections in mosquitoes. In this study, we used a high-throughput chip based on the BioMark™ Dynamic arrays system capable of detecting 64 arboviruses in a single experiment. A total of 17,958 mosquitoes collected in Zika-endemic/epidemic countries (Brazil, French Guiana, Guadeloupe, Suriname, Senegal, and Cambodia) were analyzed. Here we show that this new tool can detect endemic and epidemic viruses in different mosquito species in an epidemic context. Thus, this fast and low-cost method can be suggested as a novel epidemiological surveillance tool to identify circulating arboviruses.