Interactions between West Nile Virus and the Microbiota of Culex pipiens Vectors: A Literature Review

Characterization of Culicoides and mosquito fauna at the National Zoological Garden of Rabat, Morocco

Zoos are considering to be essential places for the conservation of wild animal species. It is essential to prevent their infection by pathogens especially for those belonging to threatened or extinct species. Zoo captive animals are susceptible to several Culicoides and mosquito borne-viruses. In order to further evaluate the risk of pathogen transmission in zoos, it is essential to identify the presence of potential vector species, as well as the animals bitten by those vectors. For this purpose, Culicoides and mosquito species composition was investigated in ten sites from March to June 2021 for Culicoides (18 collection nights) and in four sites from April to June 2022 for mosquitoes (16 collection nights) at the National Zoological Garden of Rabat (ZGR), Morocco. Culicoides (Diptera: Ceratopogonidae) were collected using Onderstepoort Veterinary Institute traps (UV-light/suction traps (OVI type)), every two weeks. Mosquitoes (Diptera: Culicidae) were collected using BG-Pro mosquito trap (BGP) combined with a CO2 source as an attractant, on two consecutive days every two weeks. The blood meal of engorged Culicoides was amplified by PCR, sequenced, and blasted for host species identification. In total, 1584 individuals belonging to the Culicoides genus were collected (88.25 % females and 11.75 % males) belonging to at least 13 different species. Among the species collected, Culicoides newsteadi (33.28 %), C. imicola (23.74 %), C. circumscriptus (18.88 %) and C. obsoletus/C. scoticus (7.96 %) constituted the majority of the total catches. These species are proven or suspected vector species of bluetongue and African hose sickness viruses in the Mediterranean basin. For mosquitoes, 455 individuals belonging to four species of three genera were collected (97.58 % females and 2.42 % males): Culex pipiens s.l. (94.29 %) (vector species of West Nile and Rift Valley fever viruses), Culiseta longiareolata (4.81 %), Aedes detritus s.l. and Ae. caspius (representing together less than 1.00 %). The results of blood meal analyses revealed that Culicoides fed on humans (n = 7), camels (n = 2), and common eland (n = 2). The composition of Culicoides and mosquito fauna is characteristic of the Rabat region. The composition is thus mostly determined by the environment rather than by the animal species presence. The results highlighted that Culicoides fed on humans and ruminants. It is therefore likely that the zoo's animals could be threatened by arboviruses transmitted by domestic animals in the region. Particular attention must be paid to the prevention of vector-borne diseases to ensure the proper conservation of species.

Vector competence of Culex quinquefasciatus from Santiago Island, Cape Verde, to West Nile Virus: exploring the potential effect of the vector native Wolbachia

BACKGROUND

Culex quinquefasciatus plays a crucial role as a vector of West Nile virus (WNV). This mosquito species is widely distributed in Cape Verde, being found in all inhabited islands of the archipelago. However, no data are currently available on the susceptibility of the local mosquito population to WNV. This study aimed to assess the vector competence of Cx. quinquefasciatus mosquitoes from Santiago Island, Cape Verde, for WNV and to explore the potential impact of its native Wolbachia on virus transmission.

METHODS

Wolbachia-infected and uninfected Cx. quinquefasciatus female mosquitoes were exposed to WNV lineage 1 PT6.39 strain using a Hemotek membrane feeding system. Mosquito samples, including the body, legs, wings and saliva, were collected at days 7, 14 and 21 post-infection (dpi) to assess WNV infection through one-step quantitative real-time PCR (RT-qPCR).

RESULTS

Culex quinquefasciatus from Cape Verde exhibited high susceptibility to the tested strain of WNV. Also, treated females without their native Wolbachia exhibited significantly higher WNV load in their bodies and greater dissemination rate at 7 dpi than their wild-type counterparts carrying Wolbachia.

CONCLUSIONS

The high susceptibility to WNV of Cx. quinquefasciatus from Cape Verde poses a potential risk for virus transmission in the archipelago. However, Wolbachia infection in this mosquito species seems to confer protection against WNV dissemination in the early stages of viral infection. Additional research is required to uncover the mechanisms driving this protection and its potential impact on WNV transmission.

The Mosquito Microbiota: A Key Player in Vector Competence and Disease Dynamics

Mosquitoes are well-known vectors for a range of pathogens, including Plasmodium parasites, which cause malaria in reptiles, birds, and mammals [...].

West Nile virus in adults and larvae of Culiseta longiareolata and Culex hortensis (Diptera: Culicidae) captured in Hamedan, western Iran

West Nile virus (WNV) is an emerging arbovirus transmitted by mosquitoes. Although it is considered the most widespread mosquito-borne arbovirus in Iran, vectors of this zoonotic pathogen remain unknown in many regions. This study aimed to assess the presence of WNV in mosquitoes collected in the western city of Hamedan in 2022. Adult mosquitoes were captured using light traps, and mosquito larvae were collected by dipping technique from 45 diverse habitats, including urban, suburban, and rural sites. Specimens were identified and pooled into 69 batches based on their species for viral RNA extraction and Real-Time PCR. In total, 3243 mosquitoes (2209 larvae and 1034 adults) were captured and identified as Culiseta longiareolata, Culex hortensis, Anopheles maculipennis s.l., Culex theileri, Culex pipiens, Anopheles claviger, and Anopheles superpictus s.l. in decreasing order. Molecular screening revealed seven WNV-positive pools of Culiseta longiareolata and Culex hortensis in rural (n = 5) and urban areas (n = 2). Detection of WNV RNA indicates active circulation in mosquitoes and risk of transmission to humans and animals in Hamadan. These findings identify putative vectors in Hamadan, though vectors likely vary regionally in Iran. Further surveillance is needed to elucidate local WNV epidemiology and transmission dynamics fully. Nonetheless, this study provides important baseline evidence of WNV activity to guide prevention strategies in this area.

Microbiota composition of Culex perexiguus mosquitoes during the West Nile virus outbreak in southern Spain

West Nile virus (WNV) is a flavivirus naturally circulating between mosquito vectors and birds, occasionally infecting horses and humans and causing epidemiologically relevant outbreaks. In Spain, the first big WNV outbreak was recorded in 2020, resulting in 77 people infected and 8 fatalities, most of them in southern Spain. Culex perexiguus was identified as the primary vector of WNV maintaining its enzootic circulation of the virus. Growing evidence highlights the role of mosquito microbiota as a key component determining the vectorial capacity of mosquitoes, largely contributing to disease epidemiology. Here, we develop, to our knowledge, the first identification of the microbiota composition of this mosquito vector under natural conditions and test for the potential relationship between mosquito microbiota composition and WNV infection. To do so, we collected mosquitoes in a natural area of southern Spain during the 2020 WNV outbreak and identified the microbiota composition of mosquitoes using a 16S rRNA gene metabarcoding approach. The microbiota of Cx. perexiguus was dominated by the phylum Proteobacteria. The most abundant families were Burkholderiaceae and Erwiniaceae, including the genera Burkholderia, Erwinia, and Pantoea. The genus Wolbachia, which use to dominate the microbiota of Cx. pipiens and negatively interact with WNV according to the literature, had a low prevalence and relative abundance in Cx. perexiguus and its abundance did not differ between WNV-positive and WNV-negative mosquito pools. The microbiota diversity and composition of Cx. perexiguus were not significantly related to the WNV infection status. These results provide the first identification of the mosquito microbiota in an endemic area of WNV circulation in Spain.

Unleashing Nature's Allies: Comparing the Vertical Transmission Dynamics of Insect-Specific and Vertebrate-Infecting Flaviviruses in Mosquitoes

Insect-specific viruses (ISVs) include viruses that are restricted to the infection of mosquitoes and are spread mostly through transovarial transmission. Despite using a distinct mode of transmission, ISVs are often phylogenetically related to arthropod-borne viruses (arboviruses) that are responsible for human diseases and able to infect both mosquitoes and vertebrates. ISVs can also induce a phenomenon called "superinfection exclusion", whereby a primary ISV infection in an insect inhibits subsequent viral infections of the insect. This has sparked interest in the use of ISVs for the control of pathogenic arboviruses transmitted by mosquitoes. In particular, insect-specific flaviviruses (ISFs) have been shown to inhibit infection of vertebrate-infecting flaviviruses (VIFs) both in vitro and in vivo. This has shown potential as a new and ecologically friendly biological approach to the control of arboviral disease. For this intervention to have lasting impacts for biological control, it is imperative that ISFs are maintained in mosquito populations with high rates of vertical transmission. Therefore, these strategies will need to optimise vertical transmission of ISFs in order to establish persistently infected mosquito lines for sustainable arbovirus control. This review compares recent observations of vertical transmission of arboviral and insect-specific flaviviruses and potential determinants of transovarial transmission rates to understand how the vertical transmission of ISFs may be optimised for effective arboviral control.

Mosquito Gut Microbiota: A Review

Mosquitoes are vectors of many important human diseases. The prolonged and widespread use of insecticides has led to the development of mosquito resistance to these insecticides. The gut microbiota is considered the master of host development and physiology; it influences mosquito biology, disease pathogen transmission, and resistance to insecticides. Understanding the role and mechanisms of mosquito gut microbiota in mosquito insecticide resistance is useful for developing new strategies for tackling mosquito insecticide resistance. We searched online databases, including PubMed, MEDLINE, SciELO, Web of Science, and the Chinese Science Citation Database. We searched all terms, including microbiota and mosquitoes, or any specific genera or species of mosquitoes. We reviewed the relationships between microbiota and mosquito growth, development, survival, reproduction, and disease pathogen transmission, as well as the interactions between microbiota and mosquito insecticide resistance. Overall, 429 studies were included in this review after filtering 8139 search results. Mosquito gut microbiota show a complex community structure with rich species diversity, dynamic changes in the species composition over time (season) and across space (environmental setting), and variation among mosquito species and mosquito developmental stages (larval vs. adult). The community composition of the microbiota plays profound roles in mosquito development, survival, and reproduction. There was a reciprocal interaction between the mosquito midgut microbiota and virus infection in mosquitoes. Wolbachia, Asaia, and Serratia are the three most studied bacteria that influence disease pathogen transmission. The insecticide resistance or exposure led to the enrichment or reduction in certain microorganisms in the resistant mosquitoes while enhancing the abundance of other microorganisms in insect-susceptible mosquitoes, and they involved many different species/genera/families of microorganisms. Conversely, microbiota can promote insecticide resistance in their hosts by isolating and degrading insecticidal compounds or altering the expression of host genes and metabolic detoxification enzymes. Currently, knowledge is scarce about the community structure of mosquito gut microbiota and its functionality in relation to mosquito pathogen transmission and insecticide resistance. The new multi-omics techniques should be adopted to find the links among environment, mosquito, and host and bring mosquito microbiota studies to the next level.

Aedes albopictus in a recently invaded area in Spain: effects of trap type, locality, and season on mosquito captures

Mosquitoes are primary vectors of pathogens impacting humans, wildlife, and livestock. Among them, the Asian tiger mosquito, Aedes albopictus, stands out as an invasive species with a global distribution, having established populations on every continent except Antarctica. Recent findings incriminate Ae. albopictus in the local transmission of several pathogens causing human diseases, including dengue, chikungunya, and Zika viruses and worm parasites as Dirofilaria. In Spain, the establishment of Ae. albopictus occurred in 2004 and it rapidly expanded, currently reaching southern provinces and creating novel epidemiological scenarios in recently invaded areas. In this study, we conducted captures of Ae. albopictus from May to November 2022 in two provinces, Granada and Malaga, situated near the current edge of the species' expanding range in Spain. The objective was to identify the primary factors influencing their captures in these regions. Mosquitoes were captured using BG-Sentinel traps baited with CO2 and BG-Lure, and miniature CDC-UV traps in five different localities. Our findings underscore the influence of both extrinsic factors, such as locality, and intrinsic factors, including mosquito sex, on the abundance of captured Ae. albopictus. A higher abundance of Ae. albopictus was observed in the Malaga province compared to localities in the Granada province. Furthermore, similar numbers of Ae. albopictus mosquitoes were captured in more urbanized areas of Granada, while the lowest counts were recorded in the less urbanized area. These results were compared to captures of another common species in the area, specifically Culex pipiens. Overall, these results represent the first monitoring of invasive Ae. albopictus in the area and are discussed in the light of the potential importance of the species as a nuisance for humans and vectors of pathogens of public health relevance.