Vector Transmission Research Articles

Houseflies (Musca domestica) as vectors of multidrug-resistant, ESBL-producing Escherichia coli in broiler poultry farms of North India: implications for antibiotic resistance transmission.

The transmission of antibiotic resistance (AR) from farm animals to healthy human communities, beyond the food chain, is often facilitated by biological vectors, notably houseflies (Musca domestica). This study aimed to evaluate the role of M. domestica collected from commercial broiler chicken farms as a carrier of multidrug-resistant (MDR), extended-spectrum β-lactamase (ESBL)-producing Escherichia coli. E. coli were isolated separately from the housefly's external surface (ES) and internal homogenate (IH) to determine the primary AR transmission route within houseflies. Remarkably, 68.6% houseflies harboured E. coli. Isolated E. coli were evaluated for susceptibility to clinically relevant antibiotics and screened for the presence of 22 plasmid-borne AR genes (ARGs) using PCR. Results revealed significant resistance to key antibiotics, with > 70% of isolates resistant to ampicillin and > 50% resistant to tetracycline and nalidixic acid in both ES- and IH-derived E. coli. Notably, a significant prevalence of resistance was observed to third-generation cephalosporins. Additionally, > 80% of E. coli isolates were MDR. A statistically significant difference (unpaired t-test, p < 0.05) was observed in the presence of ESBL-producing E. coli between the houseflies' ES (28.14%) and IH (38.14%). ARGs such as, ampC, tetA, qnrS, strA, strB, and sul3 were frequently detected in both ES- and IH-derived E. coli isolates. Among the ESBL-producing genes, blaCTX-M was the most abundant. Pearson's correlation analysis predicted the ARGs responsible for phenotypic resistance to specific antibiotics. Farm-derived flies harboured a significantly higher number of MDR E. coli (unpaired t-test, p < 0.05) than the ones isolated from flies housing a distant non-farm environment. Conclusively, this study illustrates the role of houseflies as vectors for AR transmission from AR hotspots to human communities.

Reusable Tourniquets as Potential Transmitters of Infection: A Microbiological Analysis

Introduction: Healthcare-associated infections (HAIs) pose a significant global challenge, resulting in prolonged hospital stays, higher healthcare costs, and increased morbidity and mortality rates. Reusable medical equipment, such as tourniquets, represents a potential vector for infection transmission. Despite frequent use and close contact with patients’ skin, infection control protocols often overlook these devices. This study examines microbial contamination on the surface of reusable tourniquets in both emergency department and operating theatre settings. Methods: A cross-sectional study was conducted between March and September 2024 in Gdansk, Poland. Samples from tourniquets used in the emergency department and the operating theatre were collected after an indefinite period, 14 days, and 28 days. Bacterial contamination on the surfaces of the tourniquets was measured using Columbia agar blood medium and expressed as colony-forming units (CFUs) per cm2. Results: Significant bacterial loads were detected on reusable tourniquets, with contamination levels varying by location and duration of use. The average number of CFU/cm2 across all stages of this study was 545 CFU/cm2 for the emergency department and 101 CFU/cm2 for the operating theatre. Tourniquets used in the emergency department exhibited higher bacterial counts compared to those from the operating theatre, which showed a greater diversity of bacterial species. These findings underscore the need to revise infection control protocols for reusable tourniquets. Conclusion: This study provides critical data that may influence future policy changes aimed at reducing the risk of HAIs through the improved management of reusable medical devices.

Reemerging Infectious Diseases and Neuroimmunologic Complications.

During the past decade (and beyond), neurologists have become aware of the emergence, persistence, and consequences of some familiar and new infections affecting the nervous system. Even among the familiar CNS infections, such as herpes virus, polyoma virus/JC, influenza, arbovirus, and hepatitis, challenges remain in developing effective antiviral treatments and treatments of postinfection sequelae. With the changing environment and increased global travel, arthropod vectors that mediate zoonotic disease transmission have spread unfamiliar viruses such as West Nile virus, dengue, chikungunya, equine encephalitis, and Zika, among others. Although the global health impact of these diseases has not risen to that of COVID-19 and HIV, it is likely to dramatically increase with continued spread of transmission vectors and the emergence of new zoonotic animal-to-human diseases mediated by those transmission vectors. Furthermore, specific virus-targeting treatments or effective vaccines for arboviral infections are not yet available, and this represents a major challenge in limiting the morbidity of these infections. By contrast, HIV-1, a disease that originated by direct transmission from nonhuman primates to humans (as early as the 1930s), after many years of intense study, is now targeted by highly specific and effective antiviral drugs that can limit the spread of infection and extend human life and health in all populations. Even with these dramatic therapeutic effects of suppressing HIV replication, neurologic dysfunction (primarily cognitive impairment) affects significant numbers of persons living with HIV. This emphasizes not only the importance of treating the underlying infection but also developing treatments for legacy effects of the initial infection even after antiviral therapy. Notably, the rapid emergence of SARS-CoV-2 infection was met with rapid implementation of highly effective and specific antiviral therapies. This resulted in early and dramatic lowering of the morbidity and mortality of SARS-CoV-2 infection. Nonetheless, the postinfectious complications of SARS-CoV-2 infection (long COVID) are now among the more costly consequences of emerging zoonotic infections worldwide. Developing new antiviral therapies that can penetrate the CNS, vaccines, and therapies that target host immune responses and metabolic dysfunction will be necessary for management of infectious and postinfectious complications of established and emerging infections.

Integrating One Health Strategies for Rabies Control: Insights from Jackal-Mediated Human Rabies in Northeast India

Rabies is an ancient, lethal zoonotic disease caused by viruses of the genus Lyssavirus, affecting a wide variety of mammals. Though domestic dogs are the main vectors of rabies transmission to humans, other domestic and wildlife species also contribute to the spread of the disease in endemic regions like India. This report presents a case of human rabies following jackal exposure in India, along with the molecular characterization of the rabies virus (RABV) from both the jackal and the affected human patient. RNA was extracted from brain tissue samples of a suspected rabid jackal and a 42-year-old male patient who died following exposure to the jackal. The extracted RNA was subjected to rabies-specific real-time PCR, followed by whole genome sequencing using the Illumina MiSeq platform. Phylogenetic analysis was performed using these sequences, along with other publicly available RABV whole genome sequences, with the IQ-TREE2 software and the General Time Reversible (GTR+F+I+G4) model. Real-time PCR confirmed the presence of rabies viral RNA in both the jackal and human brain samples. Whole genome sequencing yielded complete sequences of RABV from the jackal brain, and partial sequences from the human brain sample. These sequences belonged to the Arctic AL1a lineage, and were closely related to RABV strains found in dogs and other animals in India. This case underscores the potential for wildlife, such as jackals, to contribute significantly to human rabies cases and highlights the need for comprehensive surveillance and control measures to effectively combat rabies in endemic regions like India.

Relative frequency dynamics and loading of beet necrotic yellow vein virus genomic RNAs during the acquisition by its vector Polymyxa betae.

Our understanding of the transmission of plant viruses by protozoan vectors remains poor and fragmented. The fate of viral elements in the living stages of the vector is unknown. Here, we first established a protocol allowing the purification of two forms of the vector free of cellular contaminants. This permitted the examination of the relative frequencies of beet necrotic yellow vein virus RNAs in the roots of its natural host and in two forms of its protozoan vector, Polymyxa betae, responsible for virus transmission. Our findings provide new insights into virus behavior during vector transmission, allowing us to analyze how the virus regulates its RNA frequencies and load within the vector. By focusing on the early stages of viral transmission and separating virus acquisition from transmission to new hosts, we pave the way for experiments aimed at elucidating the molecular mechanisms behind viral acquisition and the maintenance of viral genome integrity by P. betae.

Identification and characterization of a Relish-type NF-κB, DvRelish, in Dermacentor variabilis in response to Rickettsia rickettsii infection.

Ixodid ticks serve as hosts and transmission vectors for several obligate intracellular bacteria, including members of the spotted fever group (SFG) of Rickettsia. Although ticks generate an immune response to bacterial insults, many of the signaling molecules associated with the response and how they may contribute to vector competence for Rickettsia are undefined. In this study, we isolated a full-length dvrelish transcript from Dermacentor variabilis, which encoded a Relish-type NF-κB. The presence of a canonical Rel homology domain (RHD) consistent with NF-κB proteins suggested a role in tick immune response for DvRelish. The expression of DvRelish was confirmed in tick tissues and fluorescent microscopy of tick hemocytes indicated increased expression following infection with Rickettsia as compared to a non-tick-borne bacterial pathogen. To further determine the effect of dvRelish gene knockdown on rickettsial infection, we used RNA interference-mediated gene knockdown in D. variabilis and demonstrated that transcription of dvRelish was decreased after 24h post-injection of siRNA. We then assessed the response of D. variabilis when exposed to Rickettsia rickettsii and determined that transcription of dvRelish was inversely associated with rickettsial loads at 48h post-exposure. Further studies are required to broaden the understanding of differential immune responses in ticks to SFG Rickettsia infection and elucidate the role played by the arthropod immune system in vector competence.

Optimizing control parameters for Huanglongbing disease in citrus orchards using SAIR-SI compartmental model, epidemic final size, and genetic algorithms

Huanglongbing (HLB) is a bacterial disease that affects citrus trees worldwide. We present an innovative approach for identifying optimal control and risk measures for HLB in citrus orchards. Our method is based on a mathematical model that incorporates the number of roguing trees and a logistic growth model for the dynamic of the Asian Citrus Psyllid (ACP), the primary vector for HLB transmission. We derive an expression for: (1) the basic reproduction number R0; (2) the final size for the number of roguing trees; and (3) the transmission risk. The above let us propose a difference map equation that assesses this final size with a low computational cost. We use this difference map in an evolutionary algorithm to identify the most effective combination of control parameter values for reducing HLB transmission, including the timing and frequency of roguing and the use of insecticides. In this sense, we propose two control strategies, which we called tree-centered and vector-centered.

Comparative Study of Gut Microbiome in Urban and Rural Eurasian Tree Sparrows.

Gut microbiota play a significant role in various physiological functions, including digestion, nutritional metabolism, and host immune function. The composition of these gut microbes is largely influenced by habitats. This study examines the gut microbiota of the Eurasian tree sparrow (Passer montanus) inhabiting rural and urban environments to understand the effects of habitat variation on microbial composition. We captured 36 rural and 29 urban adult tree sparrows and observed minor differences in body mass but substantial differences in foraging microhabitats between the two groups. Fecal samples from adult males with similar body mass were selected for a gut microbiome analysis to mitigate potential confounding effects, resulting in 20 successfully sequenced samples. The analysis disclosed disparities in gut microbiota diversity and composition between rural and urban sparrows. The urban group demonstrated slightly higher alpha diversity and distinct dominant phyla and genera compared to the rural group. Additionally, differences in the relative abundance of potentially pathogenic bacteria were observed between the groups. Several potentially pathogenic bacteria (e.g., TM7, Staphylococcus, Helicobacter, and Shigella) were more abundant in the urban group, suggesting that tree sparrows may act as transmission vectors and develop stronger immune systems. This could potentially facilitate pathogen dissemination while also contributing to the natural cycling of nutrients and maintaining ecosystem health in urban environments. The beta diversity analysis confirmed structural differences in microbial communities, implicating habitat variation as a contributing factor. Furthermore, the LEfSe analysis emphasized significant differences in gut bacteria abundance (across two phyla, three classes, six orders, seven families, and eight genera) between urban and rural sparrows, with predicted functional differences in metabolic pathways. Notably, lipid metabolism was enriched in urban sparrows, indicating enhanced lipid synthesis and metabolism in urban habitats. In conclusion, this study underscores the profound influence of habitat on the gut microbiota composition and functional potential in tree sparrows. Our findings highlight that urbanization alters the gut microbes and, consequently, the physiological functions of bird species.

Spatial analysis of malaria cases and Anopheles species in East Java region, Indonesia

Malaria remains a significant public health challenge worldwide, including in Indonesia, particularly in the East Java region. This study aimed to analyse the spatial distribution of malaria cases and Anopheles species that act as vectors in the area. Using an observational design with a cross-sectional approach, data on malaria cases were collected from tiers from the Community Health Centre, District Health Office and Province, all of which were documented on the Ministry of Health's malaria information system for the period 2021–2023. Malaria Vector Distribution Data from the East Java Health Office and the research team directly. Sampling of mosquitoes and larvae was carried out by researchers using a purposive sampling method, which prioritised locations with districts that have a high risk factor for the presence of breeding Anopheles sp., namely, Treggalek District, Malang District and Pacitan District with diverse topography, such as coastal (lagoon), rice fields and hills. The results of the analysis show that the distribution of imported malaria cases in East Java is uneven, with hotspots identified in several areas that have working population mobility from outside the East Java region. The presence of Anopheles species, particularly An. sundaicus and An. maculatus, contributes to their potential as vectors of malaria transmission, with An.sundaicus being more common in coastal areas and An. maculatus in valley and paddy fields. Environmental factors, such as topography of the region, temperature, humidity, and rainfall, influence the variation of Anopheles species. This study emphasises the importance of an ecosystem-based approach to malaria control, as well as the need to improve access to health services and community education. The findings provide important insights for the development of more effective and sustainable health policies in an effort to maintain malaria elimination areas in East Java.

Zika Virus Model with the Caputo–Fabrizio Fractional Derivative

In this article, we examine a deterministic Zika virus model that takes into account the vector and sexual transmission route, in the absence of disease-induced deaths, symmetrically observing the impact of human knowledge and vector control. In order to construct the model, we suppose that the Zika virus is first spread to humans through mosquito bites, and then to their sexual partner. In this article, we conduct analytical studies which often begin by proving the existence and uniqueness of solutions for the Zika virus model using the fractional derivative from the Caputo–Fabrizio derivative. Then, the uniqueness of the solution is investigated. After that, we also identify under which circumstances and symmetry the model provides a unique solution.

How Much Warming Can Mosquito Vectors Tolerate?

Climate warming is expected to substantially impact the global landscape of mosquito-borne disease, but these impacts will vary across disease systems and regions. Understanding which diseases, and where within their distributions, these impacts are most likely to occur is critical for preparing public health interventions. While research has centered on potential warming-driven expansions in vector transmission, less is known about the potential for vectors to experience warming-driven stress or even local extirpations. In conservation biology, species risk from climate warming is often quantified through vulnerability indices such as thermal safety margins-the difference between an organism's upper thermal limit and its habitat temperature. Here, we estimated thermal safety margins for 8 mosquito species that are the vectors of malaria, dengue, chikungunya, Zika, West Nile and other major arboviruses, across their known ranges to investigate which mosquitoes and regions are most and least vulnerable to climate warming. We find that several of the most medically important mosquito vector species, including Ae. aegypti and An. gambiae, have positive thermal safety margins across the majority of their ranges when realistic assumptions of mosquito behavioral thermoregulation are incorporated. On average, the lowest climate vulnerability, in terms of both the magnitude and duration of thermal safety, was just south of the equator and at northern temperate range edges, and the highest climate vulnerability was in the subtropics. Mosquitoes living in regions including the Middle East, the western Sahara, and southeastern Australia, which are largely comprised of desert and xeric shrubland biomes, have the highest climate vulnerability across vector species.

Risk Evaluation and Mitigation Strategies for Potential Outbreaks of Nipah Virus Infection: Evidenced by the Recent Incidences in Southeast Asian Countries.

The importance of studying Nipah virus (NiV) stems from its high fatality rates and potential for causing widespread outbreaks. Recent incidences in Southeast Asian countries highlight the urgent need for effective risk evaluation and mitigation strategies. Studying NiV in Southeast Asia is crucial due to the geographic and epidemiological significance that makes this region predominantly susceptible to the virus. This study aims to identify the risk factors of NiV, evaluate current mitigation strategies, and suggest improvements against this virus. This review incorporates articles from the PubMed database related to available NiV treatments, vaccines, mitigation strategies, transmission data, and mortality to comprise an extensive analysis of pertinent information. NiV warrants international attention, due to the high mortality rate and the rising number of human-to-human transmission vectors. NiV is difficult to diagnose early on in the infection due to its generic symptoms, and the two strains of NiV (B and M), pose significant challenges to healthcare institutions. Vaccines, such as the VSV-stored, virus-like particle-based, and mRNA-based NiV show promising results in both animal and human studies. Synthetic medicines, like Ribavirin, and favipiravir showed promising results in NiV-infected patients. Therapeutic infectious particles increased survival from 10% to roughly 70%-80% in animals. Phytochemicals, like serpentine and neoandrographolide are alternatives to NiV-G ligands. Griffithsin, an algae derivative has also shown efficacy in treating NiV infections. Artificial intelligence determines the NiV infection with an accuracy of 88.3%. The strategies to control NiV must be one of a One Health approach, incorporating environmental and social factors. Extensive research on vaccines that showed promising results in animals needs to be tested for humans on a large scale. The major mitigation strategy available is the public awareness during the outbreak about NiV transmission vectors, quarantine protocol, and food hygiene.

The global distribution and diversity of wild-bird-associated pathogens: An integrated data analysis and modeling study.

Wild birds are significant vectors in global pathogen transmission, but the diversity and spatial distribution of the pathogens detected in them remain unclear. Understanding the transmission dynamics and hotspots of wild-bird-associated pathogens (WBAPs) is crucial for early disease prevention. We compiled an up-to-date dataset encompassing all WBAPs by conducting an extensive search of publications from 1959 to 2022, mapped their diversity and global distribution, and utilized three machine learning algorithms to predict geospatial hotspots where zoonotic and emerging WBAPs were prevalent. Based on 1,834 selected studies, a total of 760 pathogens associated with 1,438 wild bird species were identified, including 387 emerging and 212 zoonotic pathogens. Migratory birds exhibited higher pathogen richness (593 species) but a lower proportion of zoonotic pathogens (27.2%) compared to resident birds (303 species and 39.3%, both p<0.01). When comparing different ecological groups, waterfowl had the highest richness of zoonotic pathogens (128 species), followed by songbirds (76 species). The distribution of WBAPs was significantly influenced by the habitat suitability index of wild birds, mammalian richness, and climatic factors. The potential geographical hotspots of zoonotic and emerging WBAPs were widely distributed in tropical areas of Asia, Africa, and South America, with zoonotic WBAPs having a wider distribution in South America. Our study illustrates that the geographical hotspots of WBAPs are more widespread than reported,especially in low-income areas, and that the identification, surveillance, and prevention of WBAP infections should be prioritized. This work was funded by the National Key Research and Development Program of China.

COORDINATION COMPOUNDS AS ANTIVIRALS AGAINST NEGLECTED TROPICAL DISEASES.

Neglected tropical viral diseases are a burden to social and economic welfare being responsible for higher pathogen-related mortality rates and chronic debilitating patient conditions. Climatic changes have widened up the infectibility ratio of such diseases, with autochthonous transmission in formerly temperate-to-cold environments. The slow-paced development of potential vaccines followed by the inexistence of antiviral drugs for such diseases considerably worsens the situation. Coordination compounds are a class of molecules that have been extensively explored as antiviral drugs for viruses such as poliovirus, HIV and, more recently, SARS-CoV-2, figuring as potential molecules to be explored and capitalized as antivirals against neglected viral strains. In this review the current efforts from the inorganic medicinal chemistry to address viral neglected tropical diseases, with emphasis to coordination compounds, is presented. Since many of neglected viruses are also arthropod-borne viruses, relying on a vector for transmission, coordination entities able to mitigate vectors are also presented as a parallel strategy to prevent and control such diseases.

Impact of Wastewater Use for Irrigation and Contamination of Lettuce by Enteric Viruses: Case of Ouagadougou Market Gardening Sites, Burkina Faso.

Raw vegetables irrigated with polluted water that may contain enteric viruses can be associated with foodborne viral disease outbreaks. The objective of this study is to investigate the possible transmission of enteric viruses from irrigation water to lettuce. Therefore, we performed a commercial multiplex real-time PCR assay to monitor the occurrence of enteric viruses in irrigation water samples and in raw vegetables that were cultivated at market gardening sites in Ouagadougou, Burkina Faso. Samples were collected from six market gardening sites located in Ouagadougou. RT-PCR was performed to detect norovirus GI, norovirus GII, rotavirus, enteric adenoviruses F (Serotype 40/41), astrovirus and sapovirus (Genogroups G1, 2, 4, 5). From the 10 irrigation water samples and the 80 lettuce samples, three (30%) and twenty-two (27.5%) were positive for enteric viruses, respectively. Norovirus GII, astrovirus and enteric adenoviruses F (Serotype 40/41) were the most frequently detected viruses in lettuce and irrigation water samples. Our results indicate that raw vegetables may be contaminated with a broad range of enteric viruses, which may originate from virus-contaminated irrigation water, and these vegetables may act as a potential vector of food-borne viral transmission.

Bacterial communities and tetracycline resistance genes in the soil-rice continuum upon tetracycline exposure

Edible plants are known as key vectors for transmission of antibiotic resistance genes (ARGs) to humans. However, little is known about how antibiotic exposure affects the abundance of ARGs in the soil-rice continuum. This study assessed tetracycline (TC) content, tetracycline resistance genes (TRGs), class 1 integron-integrase gene (intI1), and bacterial communities in the mature soil-rice continuum exposed to varying concentrations of TC (0, 50, 100, and 300 ppm). As TC exposure levels increased, the TC content in rhizosphere soils and roots increased accordingly. However, TC residue was not detected in the grains. Additionally, sample type (rhizosphere soils, roots, and grains) was the key determinant of bacterial communities and TRGs profiles in the soil-rice continuum. The bacterial communities and TRGs profiles in the rhizosphere soils and roots exposed to TC >50 ppm were more dissimilar to those without TC than to those exposed to TC <50 ppm. The abundance of TRGs in the soil-rice continuum increased with the TC concentrations but declined when TC > 50 ppm. This decline was primarily due to changes in the abundance of tetX and tetZ. Variation partitioning analysis revealed that the TRGs profiles in rhizosphere soils is strongly affected by bacterial communities. In contrast, the variation in TRGs profiles in roots was predominantly explained by bacterial communities-TC interactions. However, the changes in TRGs profiles of grains could not be attributed to the bacterial communities, TC, or intI1. This study provides valuable insights into the response of TRGs profiles in the soil-rice continuum to TC exposure.

Characterization of Tomato Leaf Curl New Delhi Virus Associated with Leaf Curl and Yellowing Disease of Bitter Gourd from Karnataka, India

Aims: The objective of this study was to identify the ToLCNDV isolate responsible for leaf curl and yellowing disease in bitter gourd crops in Karnataka, India. Study Design: Molecular characterisation and transmission study. Place and Duration of Study: The laboratory studies were conducted in the Department of Plant Pathology, College of Agriculture, University of Agricultural Sciences, GKVK, Bangalore-560065. Methodology: The sample was collected and subjected to molecular characterization using specific primer for ToLCNDV and sent for sequencing. Vector and sap transmission studies were also carried out. Results: PCR-mediated detection revealed the presence of ToLCNDV, although it was not coupled with any satellite molecules. The partial genome sequencing of the AV1 gene revealed more than 97% similarity with ToLCNDV isolates. The isolate under investigation was identified as a ToLCNDV isolate and given the name ToLCNDV_GKVK_BT due to high sequence identities and phylogenetic links between the incomplete DNA-A genome and ToLCNDV isolates. The transmission experiments demonstrated that it was effectively transmitted via vector and sap transfer. Conclusion: This study identified the ToLCNDV isolate responsible for leaf curl and yellowing disease in bitter gourd crops in Karnataka, India. Identifying, characterizing at the molecular level, and understanding the transmission of begomoviruses are essential steps in developing effective management approaches to minimize agricultural losses caused by these viruses. Therefore, these findings are important for identifying the leaf curl disease of bitter gourd.

Visions of the Desert in Atlantic Iberia: The Enigmas of Paschasius of Dumium’s Liber geronticon

ABSTRACT The apophthegmata patrum or “sayings of the desert fathers” were an essential resource for Late Antique monastics. Compiled in Greek, they quickly circulated in an array of languages, including Coptic, Syriac and Latin, connecting people across the Christian world to the imaginaire of the Egyptian desert. The sixth century saw the production of at least four Latin translations, in locations as diverse as Ostrogothic Rome and Suevic Gallaecia. This article examines one of these, the Liber geronticon produced by the monk Paschasius of Dumium in Gallaecia. Positioning this little-studied work as a window onto the vector of cultural transmission constituted by the Atlantic routes that linked the eastern Mediterranean to the Iberian Peninsula and northern Europe, it demonstrates that connectivity between the Mediterranean and Atlantic in the sixth century produced a distinctive cultural ferment, the products of which would decisively shape the desert tradition in the Iberian Peninsula and beyond.

Interplay between a polerovirus and a closterovirus decreases aphid transmission of the polerovirus.

Multi-infection of plants by viruses is very common and can change drastically infection parameters such as virus accumulation, distribution, and vector transmission. Sugar beet is an important crop that is frequently co-infected by the polerovirus beet chlorosis virus (BChV) and the closterovirus beet yellows virus (BYV), both vectored by the green peach aphid (Myzus persicae). These phloem-limited viruses are acquired while aphids ingest phloem sap from infected plants. Here we found that co-infection decreased transmission of BChV by ~50% but had no impact on BYV transmission. The drastic reduction of BChV transmission was due to neither lower accumulation of BChV in co-infected plants nor reduced phloem sap ingestion by aphids from these plants. Using the signal amplification by exchange reaction fluorescent in situ hybridization technique on plants, we observed that 40% of the infected phloem cells were co-infected and that co-infection caused redistribution of BYV in these cells. The BYV accumulation pattern changed from distinct intracellular spherical inclusions in mono-infected cells to a diffuse form in co-infected cells. There, BYV co-localized with BChV throughout the cytoplasm, indicative of virus-virus interactions. We propose that BYV-BChV interactions could restrict BChV access to the sieve tubes and reduce its accessibility for aphids and present a model of how co-infection could alter BChV intracellular movement and/or phloem loading and reduce BChV transmission.IMPORTANCEMixed viral infections in plants are understudied yet can have significant influences on disease dynamics and virus transmission. We investigated how co-infection with two unrelated viruses, BChV and BYV, affects aphid transmission of the viruses in sugar beet plants. We show that co-infection reduced BChV transmission by about 50% without affecting BYV transmission, despite similar virus accumulation rates in co-infected and mono-infected plants. Follow-up experiments examined the localization and intracellular distribution of the viruses, leading to the discovery that co-infection caused a redistribution of BYV in the phloem vessels and altered its repartition pattern within plant cells, suggesting virus-virus interactions. In conclusion, the interplay between BChV and BYV affects the transmission of BChV but not BYV, possibly through direct or indirect virus-virus interactions at the cellular level. Understanding these interactions could be crucial for managing virus propagation in crops and preventing yield losses.

Environmental determinants of West Nile virus vector abundance at the wildlife-livestock interface.

The diversity and abundance of vectors are essential parameters in the transmission dynamics of West Nile virus (WNV) between its avian reservoirs and clinically susceptible mammalian species. Knowing the determinants of vector abundance could be thus useful in preventing West Nile fever (WNF) cases and associated socio-economic impact. We designed a survey at the wildlife-livestock interface to test the hypothesis that variations in environmental favourability between anthropized and wild scenarios modulate WNV vector abundance and transmission risk. In a continental Mediterranean region where WNF has recently emerged, we selected nine sampling sites and allocated three areas to every site with a decreasing gradient of wildlife-livestock interaction: A1-a horse farm where interaction is maximal; A2-a zone of intermediate interaction 500-1000 m from the farm; and A3-an entirely wild zone of low interaction 1-5 km from the farm. At a fortnightly frequency, we estimated mosquito abundance at each of the 27 study sites in May-December 2018 and April-July 2019. We estimated bird and mammal abundance, collected meteorological information and characterised mosquito habitat at the site scale. Thereafter, we studied the determinants of Culex spp., Culex pipiens sensu lato (s.l.) Linnaeus, 1758 (Diptera: Culicidae) and Culex theileri Theobald, 1903 abundance by constructing negative binomial generalised linear mixed models. We identified 20 mosquito species, with a notable predominance of Culex spp. and, particularly, of Cx. pipiens s.l. We found differences in the spatiotemporal distribution of Culex spp. abundance and confirmed our hypothesis by finding important effects of local environmental variations in abundance. The accumulated rainfall in fortnights 4-14 and the mean temperature of the two fortnights before sampling were positively and statistically significantly associated with the abundance of Cx. pipiens s.l. (Z = 13.09, p < 0.001, and Z = 9.91, p < 0. 001, respectively) and Culex spp. (Z = 13.35, p < 0.001, and Z = 6.99, p < 0.001, respectively), while the mean temperature of the two previous fortnights was a positive statistically significant predictor (Z = 14.69, p < 0.001) of the abundance of Cx. theileri. The farm environment was the most conducive predictor to hosting Culex spp. compared with wild settings. Our results indicate that continental Mediterranean environments are favourable for WNV circulation and maintenance, especially the environment of anthropized rural settings such as farms. These results will have an impact on the spatiotemporal risk prediction of WNF emergence in continental Mediterranean environments.