Aedes albopictus is a competent vector of five arboviruses affecting human health, greater Paris, France, 2023.

Aedes albopictus collected in 2023 in the greater Paris area (Île-de-France) were experimentally able to transmit five arboviruses: West Nile virus from 3 days post-infection (dpi), chikungunya virus and Usutu virus from 7 dpi, dengue virus and Zika virus from 21 dpi. Given the growing number of imported dengue cases reported in early 2024 in France, surveillance of Ae. albopictus should be reinforced during the Paris Olympic Games in July, when many international visitors including from endemic countries are expected.

Increased threat of urban arboviral diseases from Aedes aegypti mosquitoes in Colombia.

Objectives: Our study targets the potential of the local urban mosquito Aedes aegypti to experimentally transmit chikungunya virus (CHIKV), dengue virus (DENV), yellow fever virus (YFV), and Zika virus (ZIKV). Methods: We collected eggs and adults of Ae. aegypti in Medellín, Colombia (from February to March 2020) for mosquito experimental infections with DENV, CHIKV, YFV and ZIKV and viral detection using the BioMark Dynamic arrays system. Results: We show that Ae. aegypti from Medellín was more prone to become infected, to disseminate and transmit CHIKV and ZIKV than DENV and YFV. Conclusions: Thus, in Colombia, chikungunya is the most serious threat to public health based on our vector competence data.

Evaluating vector competence for Yellow fever in the Caribbean.

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.

The Aedes aegypti RNA interference response against Zika virus in the context of co-infection with dengue and chikungunya viruses.

Since its detection in 2015 in Brazil, Zika virus (ZIKV) has remained in the spotlight of international public health and research as an emerging arboviral pathogen. In addition to single infection, ZIKV may occur in co-infection with dengue (DENV) and chikungunya (CHIKV) viruses, with whom ZIKV shares geographic distribution and the mosquito Aedes aegypti as a vector. The main mosquito immune response against arboviruses is RNA interference (RNAi). It is unknown whether or not the dynamics of the RNAi response differ between single arboviral infections and co-infections. In this study, we investigated the interaction of ZIKV and DENV, as well as ZIKV and CHIKV co-infections with the RNAi response in Ae. aegypti. Using small RNA sequencing, we found that the efficiency of small RNA production against ZIKV -a hallmark of antiviral RNAi-was mostly similar when comparing single and co-infections with either DENV or CHIKV. Silencing of key antiviral RNAi proteins, showed no change in effect on ZIKV replication when the cell is co-infected with ZIKV and DENV or CHIKV. Interestingly, we observed a negative effect on ZIKV replication during CHIKV co-infection in the context of Ago2-knockout cells, though his effect was absent during DENV co-infection. Overall, this study provides evidence that ZIKV single or co-infections with CHIKV or DENV are equally controlled by RNAi responses. Thus, Ae. aegypti mosquitoes and derived cells support co-infections of ZIKV with either CHIKV or DENV to a similar level than single infections, as long as the RNAi response is functional.

Assessing vector competence of mosquitoes from northeastern France to West Nile virus and Usutu virus.

West Nile virus (WNV) and Usutu virus (USUV) are two arthropod-borne viruses that circulate in mainland France. Assessing vector competence has only been conducted so far with mosquitoes from southern France while an increasingly active circulation of WNV and USUV has been reported in the last years. The main vectors are mosquitoes of the Culex genus and the common mosquito Culex pipiens. Here, we measure the vector competence of five mosquito species (Aedes rusticus, Aedes albopictus, Anopheles plumbeus, Culex pipiens and Culiseta longiareolata) present in northeastern France. Field-collected populations were exposed to artificial infectious blood meal containing WNV or USUV and examined at different days post-infection. We show that (i) Cx. pipiens transmitted WNV and USUV, (ii) Ae. rusticus only WNV, and (iii) unexpectedly, Ae. albopictus transmitted both WNV and USUV. Less surprising, An. plumbeus was not competent for both viruses. Combined with data on distribution and population dynamics, these assessments of vector competence will help in developing a risk map and implementing appropriate prevention and control measures.

Climate change and vector-borne diseases: a multi-omics approach of temperature-induced changes in the mosquito.

BACKGROUND: Climate change and globalization contribute to the expansion of mosquito vectors and their associated pathogens. Long spared, temperate regions have had to deal with the emergence of arboviruses traditionally confined to tropical regions. Chikungunya virus (CHIKV) was reported for the first time in Europe in 2007, causing a localized outbreak in Italy, which then recurred repeatedly over the years in other European localities. This raises the question of climate effects, particularly temperature, on the dynamics of vector-borne viruses. The objective of this study is to improve the understanding of the molecular mechanisms set up in the vector in response to temperature. METHODS: We combine three complementary approaches by examining Aedes albopictus mosquito gene expression (transcriptomics), bacterial flora (metagenomics) and CHIKV evolutionary dynamics (genomics) induced by viral infection and temperature changes. RESULTS: We show that temperature alters profoundly mosquito gene expression, bacterial microbiome and viral population diversity. We observe that (i) CHIKV infection upregulated most genes (mainly in immune and stress-related pathways) at 20°C but not at 28°C, (ii) CHIKV infection significantly increased the abundance of Enterobacteriaceae Serratia marcescens at 28°C and (iii) CHIKV evolutionary dynamics were different according to temperature. CONCLUSION: The substantial changes detected in the vectorial system (the vector and its bacterial microbiota, and the arbovirus) lead to temperature-specific adjustments to reach the ultimate goal of arbovirus transmission; at 20°C and 28°C, the Asian tiger mosquito Ae. albopictus was able to transmit CHIKV at the same efficiency. Therefore, CHIKV is likely to continue its expansion in the northern regions and could become a public health problem in more countries than those already affected in Europe.

Different viral genes modulate virulence in model mammal hosts and Culex pipiens vector competence in Mediterranean basin lineage 1 West Nile virus strains.

West Nile virus (WNV) is a single-stranded positive-sense RNA virus (+ssRNA) belonging to the genus Orthoflavivirus. Its enzootic cycle involves mosquito vectors, mainly Culex, and wild birds as reservoir hosts, while mammals, such as humans and equids, are incidental dead-end hosts. It was first discovered in 1934 in Uganda, and since 1999 has been responsible for frequent outbreaks in humans, horses and wild birds, mostly in America and in Europe. Virus spread, as well as outbreak severity, can be influenced by many ecological factors, such as reservoir host availability, biodiversity, movements and competence, mosquito abundance, distribution and vector competence, by environmental factors such as temperature, land use and precipitation, as well as by virus genetic factors influencing virulence or transmission. Former studies have investigated WNV factors of virulence, but few have compared viral genetic determinants of pathogenicity in different host species, and even fewer have considered the genetic drivers of virus invasiveness and excretion in Culex vector. In this study, we characterized WNV genetic factors implicated in the difference in virulence observed in two lineage 1 WNV strains from the Mediterranean Basin, the first isolated during a significant outbreak reported in Israel in 1998, and the second from a milder outbreak in Italy in 2008. We used an innovative and powerful reverse genetic tool, e.g., ISA (infectious subgenomic amplicons) to generate chimeras between Israel 1998 and Italy 2008 strains, focusing on non-structural (NS) proteins and the 3'UTR non-coding region. We analyzed the replication of these chimeras and their progenitors in mammals, in BALB/cByJ mice, and vector competence in Culex (Cx.) pipiens mosquitoes. Results obtained in BALB/cByJ mice suggest a role of the NS2B/NS3/NS4B/NS5 genomic region in viral attenuation in mammals, while NS4B/NS5/3'UTR regions are important in Cx. pipiens infection and possibly in vector competence.

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.

Impact of temperature on dengue and chikungunya transmission by the mosquito Aedes albopictus.

The mosquito Aedes albopictus is an invasive species first detected in Europe in Albania in 1979, and now established in 28 European countries. Temperature is a limiting factor in mosquito activities and in the transmission of associated arboviruses namely chikungunya (CHIKV) and dengue (DENV). Since 2007, local transmissions of CHIKV and DENV have been reported in mainland Europe, mainly in South Europe. Thus, the critical question is how far north transmission could occur. In this context, the Albanian infestation by Ae. albopictus is of interest because the species is present up to 1200 m of altitude; this allows using altitude as a proxy for latitude. Here we show that Ae. albopictus can transmit CHIKV at 28 °C as well as 20 °C, however, the transmission of DENV is only observed at 28 °C. We conclude that if temperature is the key environmental factor limiting transmission, then transmission of CHIKV, but not DENV is feasible in much of Europe.

A laboratory-based study to explore the use of honey-impregnated cards to detect chikungunya virus in mosquito saliva.

Mosquito control is implemented when arboviruses are detected in patients or in field-collected mosquitoes. However, mass screening of mosquitoes is usually laborious and expensive, requiring specialized expertise and equipment. Detection of virus in mosquito saliva using honey-impregnated filter papers seems to be a promising method as it is non-destructive and allows monitoring the viral excretion dynamics over time from the same mosquito. Here we test the use of filter papers to detect chikungunya virus in mosquito saliva in laboratory conditions, before proposing this method in large-scale mosquito surveillance programs. We found that 0.9 cm2 cards impregnated with a 50% honey solution could replace the forced salivation technique as they offered a viral RNA detection until 7 days after oral infection of Aedes aegypti and Aedes albopictus mosquitoes with CHIKV.

Evidence For Long-Lasting Transgenerational Antiviral Immunity in Insects.

Transgenerational immune priming (TGIP) allows memory-like immune responses to be transmitted from parents to offspring in many invertebrates. Despite increasing evidence for TGIP in insects, the mechanisms involved in the transfer of information remain largely unknown. Here, we show that Drosophila melanogaster and Aedes aegypti transmit antiviral immunological memory to their progeny that lasts throughout generations. We observe that TGIP, which is virus and sequence specific but RNAi independent, is initiated by a single exposure to disparate RNA viruses and also by inoculation of a fragment of viral double-stranded RNA. The progeny, which inherit a viral DNA that is only a fragment of the viral RNA used to infect the parents, display enriched expression of genes related to chromatin and DNA binding. These findings represent a demonstration of TGIP for RNA viruses in invertebrates, broadly increasing our understanding of the immune response, host genome plasticity, and antiviral memory of the germline.

Risk of yellow fever virus transmission in the Asia-Pacific region.

Historically endemic to Sub-Saharan Africa and South America, yellow fever is absent from the Asia-Pacific region. Yellow fever virus (YFV) is mainly transmitted by the anthropophilic Aedes mosquitoes whose distribution encompasses a large belt of tropical and sub tropical regions. Increasing exchanges between Africa and Asia have caused imported YFV incidents in non-endemic areas, which are threatening Asia with a new viral emergence. Here, using experimental infections of field-collected mosquitoes, we show that Asian-Pacific Aedes mosquitoes are competent vectors for YFV. We observe that Aedes aegypti populations from Singapore, Taiwan, Thailand, and New Caledonia are capable of transmitting YFV 14 days after oral infections, with a number of viral particles excreted from saliva reaching up to 23,000 viral particles. These findings represent the most comprehensive assessment of vector competence and show that Ae. aegypti mosquitoes from the Asia-Pacific region are highly competent to YFV, corroborating that vector populations are seemingly not a brake to the emergence of yellow fever in the region.

Experimental adaptation of dengue virus 1 to Aedes albopictus mosquitoes by in vivo selection.

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 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.

The recently introduced Aedes albopictus in Tunisia has the potential to transmit chikungunya, dengue and Zika viruses.

The mosquito Aedes albopictus was detected for the first time in Tunisia in 2018. With its establishment in the capital city of Tunis, local health authorities fear the introduction of new human arboviral diseases, like what happened in Europe with unexpected local cases of chikungunya, dengue and Zika. Even though this mosquito is competent to transmit the arboviruses mentioned above, the transmission level will vary depending on the couple, mosquito population and virus genotype. Here, we assessed the vector competence of Ae. albopictus Tunisia by experimental infections with chikungunya (CHIKV), dengue (DENV), and Zika (ZIKV) viruses. We found that Ae. albopictus Tunisia was highly competent for CHIKV (transmission efficiency of 25% at 21 post-infection) and to a lesser extent, for ZIKV (8.7%) and DENV (8.3%). Virus was detected in mosquito saliva at day 3 (CHIKV), day 10 (ZIKV) and day 21 (DENV) post-infection. These results suggest that the risk of emergence of chikungunya is the highest imposing a more sustained surveillance to limit Ae. albopictus populations in densely populated urban dwellings and at the entry points of travelers returning from CHIKV-endemic regions.

Detection of arboviruses in mosquitoes: Evidence of circulation of chikungunya virus in Iran.

Mosquitoes are vectors of viruses affecting animal and human health. In Iran, the prevalence of mosquito-borne viruses remains poorly investigated. Once infected, mosquito females remain infected for all their life making virus detections possible at early steps before infections are reported in vertebrate hosts. In this study, we used a recently developed high-throughput chip based on the BioMark Dynamic arrays system capable of detecting 37 arboviruses in a single experiment. A total of 1,212 mosquitoes collected in Mazandaran, North-Khorasan, and Fars provinces of Iran were analyzed. Eighteen species were identified, belonging to five genera; the most prevalent species were Anopheles maculipennis s.l. (42.41%), Culex pipiens (19.39%), An. superpictus (11.72%), and Cx. tritaeniorhynchus (10.64%). We detected chikungunya virus (CHIKV) of the Asian genotype in six mosquito pools collected in North Khorasan and Mazandaran provinces. To our knowledge, this is the first report of mosquitoes infected with CHIKV in Iran. Our high-throughput screening method can be proposed as a novel epidemiological surveillance tool to identify circulating arboviruses and to support preparedness to an epidemic in animals and humans.

The Aedes aegypti Domino Ortholog p400 Regulates Antiviral Exogenous Small Interfering RNA Pathway Activity and ago-2 Expression.

Arboviruses are pathogens of humans and animals. A better understanding of the interactions between these pathogens and the arthropod vectors, such as mosquitoes, that transmit them is necessary to develop novel control measures. A major antiviral pathway in the mosquito vector is the exogenous small interfering RNA (exo-siRNA) pathway, which is induced by arbovirus-derived double-stranded RNA in infected cells. Although recent work has shown the key role played by Argonaute-2 (Ago-2) and Dicer-2 (Dcr-2) in this pathway, the regulatory mechanisms that govern these pathways have not been studied in mosquitoes. Here, we show that the Domino ortholog p400 has antiviral activity against the alphavirus Semliki Forest virus (Togaviridae) both in Aedes aegypti-derived cells and in vivo Antiviral activity of p400 was also demonstrated against chikungunya virus (Togaviridae) and Bunyamwera virus (Peribunyaviridae) but not Zika virus (Flaviviridae). p400 was found to be expressed across mosquito tissues and regulated ago-2 but not dcr-2 transcript levels in A. aegypti mosquitoes. These findings provide novel insights into the regulation of an important aedine exo-siRNA pathway effector protein, Ago-2, by the Domino ortholog p400. They add functional insights to previous observations of this protein's antiviral and RNA interference regulatory activities in Drosophila melanogasterIMPORTANCE Female Aedes aegypti mosquitoes are vectors of human-infecting arthropod-borne viruses (arboviruses). In recent decades, the incidence of arthropod-borne viral infections has grown dramatically. Vector competence is influenced by many factors, including the mosquito's antiviral defenses. The exogenous small interfering RNA (siRNA) pathway is a major antiviral response restricting arboviruses in mosquitoes. While the roles of the effectors of this pathway, Argonaute-2 and Dicer-2 are well characterized, nothing is known about its regulation in mosquitoes. In this study, we demonstrate that A. aegypti p400, whose ortholog Domino in Drosophila melanogaster is a chromatin-remodeling ATPase member of the Tip60 complex, regulates siRNA pathway activity and controls ago-2 expression levels. In addition, we found p400 to have antiviral activity against different arboviruses. Therefore, our study provides new insights into the regulation of the antiviral response in A. aegypti mosquitoes.

High Transmission Potential of West Nile Virus Lineage 1 for Cx. pipiens s.l. of Iran.

: 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.

Different populations of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) from Central Africa are susceptible to Zika virus infection.

Zika virus (ZIKV) is a Flavivirus (Flaviviridae) transmitted to humans mainly by the bite of an infected Aedes mosquitoes. Aedes aegypti is the primary epidemic vector of ZIKV and Ae. albopictus, the secondary one. However, the epidemiological role of both Aedes species in Central Africa where Ae. albopictus was recently introduced is poorly characterized. Field-collected strains of Ae. aegypti and Ae. albopictus from different ecological settings in Central Africa were experimentally infected with a ZIKV strain isolated in West Africa. Mosquitoes were analysed at 14- and 21-days post-exposure. Both Ae. aegypti and Ae. albopictus were able to transmit ZIKV but with higher overall transmission efficiency for Ae. aegypti (57.9%) compared to Ae. albopictus (41.5%). In addition, disseminated infection and transmission rates for both Ae. aegypti and Ae. albopictus varied significantly according to the location where they were sampled from. We conclude that both Ae. aegypti and Ae. albopictus are able to transmit ZIKV and may intervene as active Zika vectors in Central Africa. These findings could contribute to a better understanding of the epidemiological transmission of ZIKV in Central Africa and develop suitable strategy to prevent major ZIKV outbreaks in this region.

Risk of dengue in Central Africa: Vector competence studies with Aedes aegypti and Aedes albopictus (Diptera: Culicidae) populations and dengue 2 virus.

INTRODUCTION: Dengue is the most important mosquito-borne diseases worldwide but was considered scarce in West-Central Africa. During the last decade, dengue outbreaks have increasingly been reported in urban foci in this region suggesting major epidemiological changes. However, in Central Africa where both vectors, Aedes aegypti and Aedes albopictus are well established, the role of each species in dengue transmission remains poorly investigated. METHODOLOGY/PRINCIPAL FINDINGS: Field-collected strains of Ae. aegypti and Ae. albopictus from different ecological settings in Central Africa were experimentally challenged with dengue 2 virus (DENV-2). Mosquitoes were analysed at 14- and 21-days post-infection. Analysis provide evidence that both Ae. aegypti and Ae. albopictus in Central Africa were able to transmit dengue virus with Ae. aegypti exhibiting a higher transmission rate. Unexpectedly, two Ae. aegypti populations from Bénoué and Maroua, in northern Cameroon, were not able to transmit DENV-2. CONCLUSIONS/SIGNIFICANCE: We conclude that both Ae. aegypti and Ae. albopictus are susceptible to DENV-2 and may intervene as active dengue vectors. These findings highlight the urgent need to plan a vector surveillance program and control methods against dengue vectors in Central Africa in order to prevent future outbreaks.

Zika virus threshold determines transmission by European Aedes albopictus mosquitoes.

Since its emergence in Yap Island in 2007, Zika virus (ZIKV) has affected all continents except Europe. Despite the hundreds of cases imported to European countries from ZIKV-infested regions, no local cases have been reported in localities where the ZIKV-competent mosquito Aedes albopictus is well established. Here we analysed the vector competence of European Aedes (aegypti and albopictus) mosquitoes to different genotypes of ZIKV. We demonstrate that Ae. albopictus from France was less susceptible to the Asian ZIKV than to the African ZIKV. Critically we show that effective crossing of anatomical barriers (midgut and salivary glands) after an infectious blood meal depends on a viral load threshold to trigger: (i) viral dissemination from the midgut to infect mosquito internal organs and (ii) viral transmission from the saliva to infect a vertebrate host. A viral load in body ≥4800 viral copies triggered dissemination and ≥12,000 viral copies set out transmission. Only 27.3% and 18.2% of Ae. albopictus Montpellier mosquitoes meet respectively these two criteria. Collectively, these compelling results stress the poor ability of Ae. albopictus to sustain a local transmission of ZIKV in Europe and provide a promising tool to evaluate the risk of ZIKV transmission in future outbreaks.