Endogenous non-retroviral elements in genomes of Aedes mosquitoes and vector competence

Recent extensive (re)emergences of arthropod-borne viruses (arboviruses) such as chikungunya (CHIKV), zika (ZIKV) and dengue (DENV) viruses highlight the role of the epidemic vectors, Aedes aegypti and Aedes albopictus, in their spreading. Differences of vector competence to arboviruses highlight different virus/vector interactions. While both are highly competent to transmit CHIKV (Alphavirus,Togaviridae), only Ae. albopictus is considered as a secondary vector for DENV (Flavivirus, Flaviviridae). Among other factors such as environmental temperature, mosquito antiviral immunity and microbiota, the presence of non-retroviral integrated RNA virus sequences (NIRVS) in both mosquito genomes may modulate the vector competence. Here we review the current knowledge on these elements, highlighting the mechanisms by which they are produced and endogenized into Aedes genomes. Additionally, we describe their involvement in antiviral immunity as a stimulator of the RNA interference pathways and in some rare cases, as producer of viral-interfering proteins. Finally, we mention NIRVS as a tool for understanding virus/vector co-evolution. The recent discovery of endogenized elements shows that virus/vector interactions are more dynamic than previously thought, and genetic markers such as NIRVS could be one of the potential targets to reduce arbovirus transmission

Orally Co-Infected Aedes albopictus from La Reunion Island, Indian Ocean, Can Deliver Both Dengue and Chikungunya Infectious Viral Particles in Their Saliva

Dengue (DEN) and chikungunya (CHIK) are two mosquito borne infections transmitted by Aedes mosquitoes in the tropical world. Ae. albopictus has been shown to efficiently transmit the new variant of CHIK virus (CHIKV) that emerged in the Indian Ocean region in 2005. At the same time, this vector is able to sustain outbreaks due to DEN virus (DENV). Since this CHIK emergence, co-infections DENV-CHIKV in humans have been regularly reported. This phenomenon, known for a long time, may be due to two consecutive bites from two mosquitoes infected by one virus or by the bite of a mosquito infected by both viruses. We used two viral strains isolated in La Reunion Island, DENV-1 in 2004 and CHIKV in 2005, and co-infected an autochthonous strain of Ae. albopictus, testing experimentally one of the possible ways to get co-infections in humans. We were able to show the ability of Ae. albopictus to replicate simultaneously both arboviruses and, furthermore, to deliver both infectious viral particles concomitantly in their saliva. This finding is of particular interest since Ae. albopictus is now widely distributed all around the world and still expanding its geographical range

Differential responses of the mosquito Aedes albopictus from the Indian Ocean region to two chikungunya isolates

International audienceBACKGROUND: Aedes aegypti and Aedes albopictus are both vectors of chikungunya virus (CHIKV). The two Aedes species co-exist in the Indian Ocean region and were involved in the 2005-2006 CHIKV outbreaks. In the Reunion Island, a single mutation in the viral envelope has been selected that leads to high levels of replication in Ae. albopictus, and a short extrinsic incubation period as the virus could be found in saliva as early as two days after infection. An important question is whether this variant is associated with adverse effects impacting some mosquito life-history traits such as survival and reproduction. RESULTS: We performed experimental infections using three mosquito strains of Ae. aegypti Mayotte and Ae. albopictus (Mayotte and Reunion), and two CHIKV strains (E1-226A and E1-226V). Ae. aegypti Mayotte were similarly susceptible to both viral strains, whereas Ae. albopictus Mayotte and Ae. albopictus Reunion were more susceptible to CHIKV E1-226V than to E1-226A. In terms of life-history traits measured by examining mosquito survival and reproduction, we found that: (1) differences were observed between responses of mosquito species to the two viruses, (2) CHIKV infection only affected significantly some life-history traits of Ae. albopictus Reunion and not of the other two mosquito strains, and (3) CHIKV reduced the lifespan of Ae. albopictus Reunion and shortened the time before egg laying. CONCLUSION: We demonstrated that CHIKV only reduces the survival of Ae. albopictus from the Reunion Island. By laying eggs just before death, reproduction of Ae. albopictus from the Reunion Island is not reduced since other parameters characterizing oviposition and hatching were not affected

Culex quinquefasciatus mosquitoes do not support replication of Zika virus

The rapid spread of Zika virus (ZIKV) in the Americas raised many questions about the role of Culex quinquefasciatus mosquitoes in transmission, in addition to the key role played by the vector Aedes aegypti. Here we analysed the competence of Cx. quinquefasciatus (with or without Wolbachia endosymbionts) for a ZIKV isolate. We also examined the induction of RNA interference pathways after viral challenge and the production of small virus-derived RNAs. We did not observe any infection nor such small virus-derived RNAs, regardless of the presence or absence of Wolbachia. Thus, Cx. quinquefasciatus does not support ZIKV replication and Wolbachia is not involved in producing this phenotype. In short, these mosquitoes are very unlikely to play a role in transmission of ZIKV

Vector competence of Aedes japonicus for chikungunya and dengue viruses

The Asian bush mosquito Aedes japonicus japonicus (Theobald, 1901) [=Ochlerotatus japonicus (sensu Reinert et al., 2004) =Hulecoeteomyia japonica (sensu Reinert et al., 2006)], has invaded large parts of North America and has recently started to spread in Central-Western Europe. The species is suspected to act as a bridge vector of West Nile virus but nothing or very little is known about its vector competence for Chikungunya and Dengue viruses. Here, we report on experiments of laboratory infections of Ae. japonicus with CHIKV and DENV, demonstrating that the species has a vector potential for both viruses. Considering the high abundance of the species in urban environments and its ability to feed on human, these results plead to include this species when processing risk assessments for mosquito-borne diseases

Characterization of <i>Aedes aegypti</i> innate-immune pathways that limit Chikungunya virus replication

Replication of arboviruses in their arthropod vectors is controlled by innate immune responses. The RNA sequence-specific break down mechanism, RNA interference (RNAi), has been shown to be an important innate antiviral response in mosquitoes. In addition, immune signaling pathways have been reported to mediate arbovirus infections in mosquitoes; namely the JAK/STAT, immune deficiency (IMD) and Toll pathways. Very little is known about these pathways in response to chikungunya virus (CHIKV) infection, a mosquito-borne alphavirus (Togaviridae) transmitted by aedine species to humans resulting in a febrile and arthralgic disease. In this study, the contribution of several innate immune responses to control CHIKV replication was investigated. In vitro experiments identified the RNAi pathway as a key antiviral pathway. CHIKV was shown to repress the activity of the Toll signaling pathway in vitro but neither JAK/STAT, IMD nor Toll pathways were found to mediate antiviral activities. In vivo data further confirmed our in vitro identification of the vital role of RNAi in antiviral defence. Taken together these results indicate a complex interaction between CHIKV replication and mosquito innate immune responses and demonstrate similarities as well as differences in the control of alphaviruses and other arboviruses by mosquito immune pathways

Accurate identification of Culicidae at aquatic developmental stages by MALDI-TOF MS profiling

International audienceBACKGROUND: The identification of mosquito vectors is generally based on morphological criteria, but for aquatic stages, morphological characteristics may be missing, leading to incomplete or incorrect identification. The high cost of molecular biology techniques requires the development of an alternative strategy. In the last decade, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) profiling has proved to be efficient for arthropod identification at the species level.METHODS:To investigate the usefulness of MALDI-TOF MS for the identification of mosquitoes at aquatic stages, optimizations of sample preparation, diet, body parts and storage conditions were tested. Protein extracts of whole specimens from second larval stage to pupae were selected for the creation of a reference spectra database. The database included a total of 95 laboratory-reared specimens of 6 mosquito species, including Anopheles gambiae (S form), Anopheles coluzzi (M form), Culex pipiens pipiens, Culex pipiens molestus, Aedes aegypti and 2 colonies of Aedes albopictus.RESULTS:The present study revealed that whole specimens at aquatic stages produced reproducible and singular spectra according to the mosquito species. Moreover, MS protein profiles appeared weakly affected by the diet provided. Despite the low diversity of some MS profiles, notably for cryptic species, clustering analyses correctly classified all specimens tested at the species level followed by the clustering of early vs. late aquatic developmental stages. Discriminant mass peaks were recorded for the 6 mosquito species analyzed at larval stage 3 and the pupal stage. Querying against the reference spectra database of 149 new specimens at different aquatic stages from the 6 mosquito species revealed that 147 specimens were correctly identified at the species level and that early and late developmental stages were also distinguished.CONCLUSIONS:The present work highlights that MALDI-TOF MS profiling may be useful for the rapid and reliable identification of mosquito species at aquatic stages. With this proteomic tool, it becomes now conceivable to survey mosquito breeding sites prior to the mosquitoes' emergence and to adapt anti-vectorial measures according to the mosquito fauna detected

European Aedes caspius mosquitoes are experimentally unable to transmit Zika virus

Background: Aedes caspius (Pallas, 1771) is a foodwater mosquito species widely distributed in the Western Palae‑ arctic. As an anthropophilic species, its role as an arbovirus vector may be the key for understanding the transmission cycle of certain diseases in Europe such as Zika virus (ZIKV). Concerning vector competence for ZIKV, studies related to Ae. caspius are still scarce. ZIKV is an arbovirus that has provoked a widespread epidemic in the Pacifc region (2007– 2013) and in the Americas (2015–2016). ZIKV is associated with serious neurological injuries (e.g. microcephaly) and Guillain-Barré syndrome. Due to the ZIKV epidemics in the American continent, some viraemic travellers coming from endemic countries have been reported in Europe. More knowledge is therefore required to defne the susceptibility of autochthonous mosquito species such as Ae. caspius for ZIKV in order to improve arbovirus surveillance and control programmes. In the present study, the vector competence of a European population of Ae. caspius was evaluated for two ZIKV lineages, the Suriname ZIKV strain (Asian lineage) and the MR766 ZIKV strain (African I lineage). Females were tested at 7, 14 and 21 days post-exposure (dpe) to infectious blood meals. An Ae. aegypti PAEA strain was used as a positive control. Results: Aedes caspius presented low susceptibility to ZIKV infection and the virus was only detected by RT-qPCR in body samples. Low viral loads were detected for the MR766 strain at 7 dpe and for the Suriname strain at 14 and 21 dpe. Aedes caspius was unable to produce a disseminated infection and virus transmission at any of the tested time points. Using Ae. aegypti PAEA strain, infection, dissemination and transmission rates were calculated for the Suriname ZIKV strain (Asian lineage) at each time point. For the MR766 ZIKV strain (African I lineage), while only infection rates were estimated at each time point, no dissemination or transmission were detected in either species. Conclusions: The results of the present study reveal that the tested Ae. caspius population has a strong midgut escape barrier that limits the dissemination or transmission of the virus. As such, it seems unlikely that European Ae. caspius mosquitoes could be involved in ZIKV transmission if ZIKV was introduced into Europe. This information may help in designing a better strategy to European surveillance and control programmes for ZIKV.info:eu-repo/semantics/publishedVersio