Bluetongue and Epizootic Hemorrhagic Disease in the United States of America at the Wildlife-Livestock Interface

A habitat suitability analysis for three Culicoides species implicated in bluetongue virus transmission in the Southeastern United States

Culicoides biting midges adversely impact animal health through transmission of multiple orbiviruses, such as bluetongue virus (BTV). This study used light trapping data collected in the Southeastern United States for three Culicoides midge species that are confirmed or suspected BTV vectors: Culicoides insignis, Culicoides stellifer and Culicoides venustus. Midge presence datasets were combined with meteorological data and ecological data to model habitat suitability for each species. Logistic regression and machine learning models were used to generate individual species distribution models (SDMs). Results for each SDM method were combined in an ensemble model to create a distribution model for each midge species. Based on overlay analyses of livestock populations and midge suitable habitat, there is extensive overlap of cattle and goat populations and suitable habitat for C. insignis in Florida. Suitable habitat for C. stellifer intersects with cattle and goat populations in various counties in Alabama, Arkansas, the Carolinas, Florida, Georgia, Louisiana and Tennessee; and suitable habitat for C. venustus intersects with cattle and goat populations in the same states as C. stellifer, except for Florida. It is critical for orbivirus and midge surveillance to continue in the Southeastern United States as the habitat of all three midge species intersect with livestock populations.

Bluetongue's New Frontier-Are Dogs at Risk?

Bluetongue virus (BTV), traditionally considered a pathogen of ruminants, has recently been documented in dogs, challenging conventional understanding of its epidemiology. This narrative review synthesizes emerging evidence regarding BTV infections in domestic and wild carnivores, examining transmission dynamics, pathogenesis, clinical manifestations, and diagnostic challenges. Carnivores can become infected through vector transmission and oral ingestion of infected material. While some infected carnivores remain subclinical, others develop severe clinical manifestations including hemorrhagic syndromes. BTV infection in carnivores is likely underdiagnosed due to limited awareness, nonspecific clinical signs, and absence of established diagnostic protocols for non-ruminant species. The potential role of carnivores in BTV epidemiology remains largely unexplored, raising questions about their function as reservoirs or dead-end hosts. Additionally, carnivores may contribute to alternative transmission pathways and overwintering mechanisms that impact disease ecology. Current biosecurity frameworks and surveillance systems, primarily focused on ruminants, require expansion to incorporate carnivores in viral maintenance and transmission. This review identifies significant knowledge gaps regarding BTV in carnivores and proposes future research directions, including serological surveys, transmission studies, and investigation of viral tropism in carnivore tissues. A comprehensive One Health approach integrating diverse host species, vector ecology, human interference, and environmental factors is crucial for effective BTV control and impact mitigation on human, animals, and environment.

Epizootic hemorrhagic disease virus oral infection affects midge reproduction and is vertically transmitted to offspring in Culicoides sonorensis

Epizootic hemorrhagic disease virus (EHDV: Reoviridae: Orbivirus) is a Culicoides-borne pathogen that affects a variety of ruminants, causing significant economic losses and/or ecological impacts in animal agriculture/wildlife populations worldwide. In this study, we examined the effect of EHDV serotype-2 oral infection on the survival and reproduction of Culicoides sonorensis Wirth and Jones (a confirmed vector of EHDV in North America), and the potential vertical transmission of EHDV-2 (from infected female to its offspring) in this midge species. Culicoides sonorensis females were fed on defibrinated bovine blood mixed with EHDV-2 (5.5 log10 PFU/ml) or without EHDV-2 (control). Adult survival/longevity, oviposition rates, number of eggs deposited, egg hatch rates (fertility), larval survival, larval stage duration, eclosion rates, and sex-ratios of the progeny were recorded and compared between the two groups. In addition, the progeny (eggs and F1 generation adults) of EHDV-2 fed females were processed for viral detection through RT-qPCR and plaque assays. Survival/longevity of the blood-fed adults, oviposition rates, number of eggs deposited, larval stage duration, eclosion rates, and sex-ratios were not significantly different between the two groups. However, egg hatch rates were significantly lower in the EHDV-2 fed group (35.8 ± 5.2%) than the control group (74.5 ± 6.8%), but larval survival rates were higher in the EHDV-2 fed group (59.8 ± 4.9%) compared to the control group (34.1 ± 6.5%). EHDV-2 (Ct < 35) was detected in the eggs (3.4%, 1/29 females tested, Ct = 22.1 [4.9 log10 PFUe/ml]) and F1 adult progeny (1.7%, 1/58 adults tested, Ct = 23.5 [4.5 log10 PFUe/ml]) of the orally exposed females through RT-qPCR as well as through plaque assays. Our findings suggest that EHDV-2 infection has no major impact on C. sonorensis survival/longevity or oviposition but has a significant negative effect on midge fecundity/fertility. Our study also provides evidence for the vertical transmission of EHDV-2 from an infected adult female to its offspring in C. sonorensis. However, salivary transmission of EHDV-2 from the vertically infected progeny and its significance in the epidemiology of hemorrhagic disease are currently unknown and remain to be examined in further studies. Overall, these findings collectively indicate that Orbivirus infection can negatively affect vector reproduction, and that vertical transmission is a probable mechanism of overwintering of EHDV in North America.

Understanding the Burden of Agriculturally Significant Vector-Borne and Parasitic Diseases in Kansas

Background: The state of Kansas (KS) has been called the "agricultural heartland" of the United States. Vector-borne and parasitic diseases (VBPD) have a major impact on the production of livestock, such as cattle, swine, goats and sheep, as well as crops, such as wheat, corn, and sorghum. The purpose of this review is to educate agricultural professionals in the state of KS about VBPD of current or potential concern and to inform the public about the challenges faced by the agricultural community. Methods: This review describes and discusses the endemic VBPD that currently impact agricultural production in KS and foreign VBPD of concern. In addition, we outline the major arthropod vectors of VBPD in KS, including ticks, mites, and various insects. In the context of this review, parasites are strictly limited to arthropod ectoparasites that negatively impact livestock production. Modern agricultural data for the state of KS were mostly sourced from the USDA National Agricultural Statistics Service, and current KS VBPD data were mostly sourced from the KS State Veterinary Diagnostic Laboratory. Conclusion: These VBPD have a large economic impact on the state and country, and we have concluded there is a need for updated estimates regarding the economic burden of VBPD in KS and throughout the United States to make better animal and crop health investment decisions.

A Novel Ephemero- and a New CHeRI Orbivirus Isolated from a Dead Farmed White-Tailed Deer (Odocoileus virginianus) in Florida, USA

A novel ephemeral fever rhabdovirus and a CHeRI orbivirus of a previously unidentified genetic lineage were isolated in mosquito cell line C6/36 cells as co-infecting agents from the spleen tissue of a dead farmed white-tailed deer (WTD; Odocoileus virginianus) in Florida. We designated the ephemeral fever rhabdovirus as Hardee County ephemerovirus 1, strain CHeRI ephemerovirus 1. The genetic sequences of the CHeRI orbivirus isolated in this work differ significantly from those of three previously described CHeRI orbivirus lineages. We designated this new virus as CHeRI orbivirus 4, strain CHeRI orbivirus 4-1. Whereas it remains unknown whether one, both, or none of the viruses contributed to the pathology, gross observations revealed that the dead WTD had severely congested and hemorrhagic lungs, and that its heart, kidneys, and spleen were also congested.

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.

The Global Burden of Emerging and Re-Emerging Orbiviruses in Livestock: An Emphasis on Bluetongue Virus and Epizootic Hemorrhagic Disease Virus

Bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV) are vector-borne orbiviruses that pose an emerging threat to livestock, including cattle and sheep. This review summarizes the global distribution, genetic diversity, and key factors driving their spread along with the existing knowledge gaps and recommendations to mitigate their impact. Both viruses cause hemorrhagic disease in susceptible ruminants and are commonly reported in tropical and subtropical regions including North America, Asia, Africa, Oceania, and some parts of Europe. The geographical distribution of these viruses, encompassing 27 BTV and 7 EHDV serotypes, has shifted, particularly with the recent invasion of BTV-3, 4, and 8 and EHDV-8 serotypes in Europe. Several factors contribute to the recent spread of these viruses such as the distribution of virulent strains by the movement of temperature-dependent Culicoides vectors into new areas due to rapid climate change, the reassortment of viral strains during mixed infections, and unrestricted global trade. These diseases cause significant economic impacts including morbidity, mortality, reduced production, high management costs, and the disruption of international trade. Effective prevention and control strategies are paramount and rely on vaccination, vector control using insecticides, and the destruction of breeding sites, husbandry practices including the isolation and quarantine of infected hosts, restriction of animal movement, prompt diagnosis and identification of circulating strains, and effective surveillance and monitoring plans such as the pre-export and post-import screening of semen used for artificial insemination. However, challenges remain with intercontinental virus spread, live vaccines, and the failure of inactivated vaccines to produce protective immunity against dissimilar strains. Significant knowledge gaps highlight the need for a better scientific understanding and a strategic plan to ensure healthy livestock and global food security.

Vaccine candidates based on MVA viral vectors expressing VP2 or VP7 confer full protection against Epizootic hemorrhagic disease virus in IFNAR(-/-) mice

Epizootic hemorrhagic disease (EHD), caused by Epizootic hemorrhagic disease virus (EHDV), is an emerging and severe livestock disease. Recent incursion and distribution of EHDV in Europe have outlined the need for vaccine research against this viral disease. In this work, we report modified vaccinia virus Ankara (MVA)-vectored vaccines designed to express protein VP2 of EHDV-8 or protein VP7 of EHDV-2. Prime boost immunization of adult IFNAR(-/-) mice with the MVA-VP2 vaccine candidate induced high titers of EHDV-8-specific neutralizing antibodies (NAbs) and conferred full protection against homologous lethal challenge with EHDV-8. However, no heterologous protection was observed after lethal challenge with EHDV-6. In contrast, the MVA-VP7 vaccine candidate elicited strong cytotoxic CD8+ T-cell responses against VP7 and conferred complete protection against lethal challenge with either EHDV-8 or EHDV-6 in IFNAR(-/-) mice in the absence of NAbs, being the first multiserotype vaccine candidate against EHDV. Moreover, we expressed recombinant proteins VP2 and VP7 of EHDV in the baculovirus expression system, which were used to analyze the potential DIVA (differentiating infected from vaccinated animals) character of these vaccine candidates.IMPORTANCEEmergence and re-emergence of arthropod-borne viruses are major concerns for both human and animal health. The most recent example is the fast expansion of EHDV-8 through Europe. Besides, EHDV-8 relates with a high prevalence of pathologic cases in cattle populations. No vaccine is currently available in Europe, and vaccine research against this arboviral disease is negligible. In this work, we present novel DIVA vaccine candidates against EHDV, and most importantly, we identified the protein VP7 of EHDV as an antigen capable of inducing multiserotype protection, one of the major challenges in vaccine research against orbiviruses.

Assessing the Risk of Windborne Dispersal of Culicoides Midges in Emerging Epizootic Hemorrhagic Disease Virus Outbreaks in France

The epizootic hemorrhagic disease virus (EHDV) is a novel emerging threat for the European livestock sector. First detected in Sardinia and southern Spain at the end of 2022, this transboundary disease emerged in France in September 2023 despite restrictions on animal movement and enhanced surveillance protocols. Although virus spread is believed to be mediated by the dispersal of Culicoides vectors by the wind, prediction is difficult due to the large number of meteorological parameters that must be considered. Using simulations of atmospheric trajectories, we developed a model to investigate the long-distance dispersal risk zone of Culicoides in Europe, starting from different source zones. Our model predicted with good sensitivity the newly EHDV-infected areas in France over a period of 5 weeks after its first introduction in the country. Prospectively, we predicted that the midge dispersal zone of early 2024 could expand toward most of the western half of France and could sporadically reach new countries under favorable spring conditions. The wind dispersal risk maps provided are intended to support better preparedness and response to Culicoides-borne diseases.

IFNAR(-/-) Mice Constitute a Suitable Animal Model for Epizootic Hemorrhagic Disease Virus Study and Vaccine Evaluation

Epizootic hemorrhagic disease (EHD), caused by Epizootic hemorrhagic disease virus (EHDV), is an emerging and severe livestock disease. Recent incursion and distribution of EHDV in Europe have outlined the emerging character of EHD. Despite its worldwide impact, numerous knowledge gaps exist. A range of inconveniences restricts utilization of natural hosts of EHDV. Here, we show that adult mice deficient in type I IFN receptor (IFNAR(-/-)) are highly susceptible to EHDV-6 and EHDV-8 infection when the virus is administered subcutaneously. Disease was characterized by ruffled hair, reluctance to move, dehydration and conjunctivitis, with viraemia detected from day 5 post-infection. A deeper characterization of EHDV-8 infection showed viral replication in the lung, liver, spleen, kidney, testis and ovaries. Importantly, increased expression levels of pro-inflammatory cytokines IL-1β, IL-6 and CXCL2 were observed in spleen after EHDV-8 infection. Furthermore, IFNAR(-/-) adult mice immunized with a EHDV-8 inactivated vaccine elicited neutralizing antibodies specific of EHDV-8 and full protection against challenge with a lethal dose of this virus. This study also explores the possibilities of this animal model for study of BTV and EHDV coinfection. In summary, the IFNAR(-/-) mouse model faithfully recapitulates EHD and can be applied for vaccine testing, which can facilitate progress in addressing the animal health challenge posed by this virus.

The Molecular Epidemiology of Epizootic Hemorrhagic Disease Viruses Identified in Israel between 2015 and 2023

Epizootic hemorrhagic disease (EHD) is an infectious, non-contagious viral disease seriously affecting cattle and some wild ruminants and has a worldwide distribution. All viruses can be subdivided into "Eastern" and "Western" topotypes according to geographic distribution via the phylogenetic analysis of internal genes. In Israel, during the last decade, three outbreaks were registered: caused by EHDV-6 in 2015, by EHDV-1 in 2016, and by EHDV-7 in 2020. Additionally, RNA of EHDV-8 was found in imported calves from Portugal in 2023. During the same period in other countries of the region, non-Israeli-like EHDV-6 and EHDV-8 were identified. Full genome sequencing, BLAST, and phylogenetic analyses of the locally and globally known EHDV genomes allowed us to presume the probable route and origin of these viruses detected in Israel. Thus, EHDV-6 has probably been circulating in the region for a long period when EHDV-1 and -8 appeared here for the last years, while their route of introduction into the new areas was probably natural; all of them belonged to the "Western" topotype. In contrast, EHDV-7 probably had the "Eastern", anthropogenic origin. Data from the study can facilitate the evaluation of the appearance or reappearance of EHDVs in the Mediterranean area and enhance the planning of prevention measures.

The Study of Bluetongue Virus (BTV) and Epizootic Hemorrhagic Disease Virus (EHDV) Circulation and Vectors at the Municipal Parks and Zoobotanical Foundation of Belo Horizonte, Minas Gerais, Brazil (FPMZB-BH)

Bluetongue Virus (BTV) and Epizootic Hemorrhagic Disease Virus (EHDV) are Orbiviruses primarily transmitted by their biological vector, Culicoides spp. Latreille, 1809 (Diptera: Ceratopogonidae). These viruses can infect a diverse range of vertebrate hosts, leading to disease outbreaks in domestic and wild ruminants worldwide. This study, conducted at the Belo Horizonte Municipal Parks and Zoobotany Foundation (FPMZB-BH), Minas Gerais, Brazil, focused on Orbivirus and its vectors. Collections of Culicoides spp. were carried out at the FPMZB-BH from 9 December 2021 to 18 November 2022. A higher prevalence of these insects was observed during the summer months, especially in February. Factors such as elevated temperatures, high humidity, fecal accumulation, and proximity to large animals, like camels and elephants, were associated with increased Culicoides capture. Among the identified Culicoides spp. species, Culicoides insignis Lutz, 1913, constituted 75%, and Culicoides pusillus Lutz, 1913, 6% of the collected midges, both described as competent vectors for Orbivirus transmission. Additionally, a previously unreported species in Minas Gerais, Culicoides debilipalpis Lutz, 1913, was identified, also suspected of being a transmitter of these Orbiviruses. The feeding preferences of some Culicoides species were analyzed, revealing that C. insignis feeds on deer, Red deer (Cervus elaphus) and European fallow deer (Dama dama). Different Culicoides spp. were also identified feeding on humans, raising concerns about the potential transmission of arboviruses at the site. In parallel, 72 serum samples from 14 susceptible species, including various Cervids, collected between 2012 and 2022 from the FPMZB-BH serum bank, underwent Agar Gel Immunodiffusion (AGID) testing for BTV and EHDV. The results showed 75% seropositivity for BTV and 19% for EHDV. Post-testing analysis revealed variations in antibody presence against BTV in a tapir and a fallow deer and against EHDV in a gemsbok across different years. These studies confirm the presence of BTV and EHDV vectors, along with potential virus circulation in the zoo. Consequently, implementing control measures is essential to prevent susceptible species from becoming infected and developing clinical diseases.

A novel bluetongue virus serotype 2 strain isolated from a farmed Florida white-tailed deer (Odocoileus virginianus) arose from reassortment of gene segments derived from co-circulating serotypes in the Southeastern USA

Bluetongue disease is a reportable animal disease that affects wild and farmed ruminants, including white-tailed deer (WTD). This report documents the clinical findings, ancillary diagnostics, and genomic characterization of a novel reassortant bluetongue virus serotype 2 (BTV-2) strain isolated from a dead Florida farmed WTD in 2022. Our analyses support that this BTV-2 strain likely stemmed from the acquisition of genome segments from co-circulating BTV strains in Florida and Louisiana. In addition, our analyses also indicate that genetically uncharacterized BTV strains may be circulating in the Southeastern USA; however, the identity and reassortant status of these BTV strains cannot be determined based on the VP2 and VP5 genome sequences. Hence, continued surveillance based on complete genome characterization is needed to understand the genetic diversity of BTV strains in this region and the potential threat they may pose to the health of deer and other ruminants.

Recovery of multireassortant bluetongue virus serotype 6 sequences from a mule deer (Odocoileus hemionus) and Dorset sheep (Ovis aries) in Colorado

We report the discovery of two bluetongue virus serotype 6 (BTV-6) reassortants recovered from a domestic sheep and a free-ranging mule deer in northern Colorado. At the time of this publication, whole-genome sequencing of BTV-6 isolates in the Western U.S. have not been undertaken. These findings reflect the incursive movement of geographically distinct BTV serotypes into important agricultural areas of the U.S. and demonstrate reassortment with regionally circulating serotypes.

Detection, Characterization and Sequencing of BTV Serotypes Circulating in Cuba in 2022

In Cuba, despite a high sero-prevalence of bluetongue virus (BTV), circulating serotypes remain unknown. The aim of this study was to identify circulating BTV serotypes in farms throughout the western region of Cuba. Blood samples were collected from 200 young cattle and sheep between May and July 2022 for virological analyses (PCR, viral isolation and virus neutralization) and genome sequencing. The results confirmed viral circulation, with viro-prevalence of 25% for BTV. The virus was isolated from 18 blood samples and twelve BTV serotypes were identified by sequencing RT-PCR products targeting the segment 2 of the BTV genome (BTV-1, 2, 3, 6, 10, 12, 13, 17, 18, 19, 22 and 24). Finally, the full genome sequences of 17 Cuban BTV isolates were recovered using a Sequence Independent Single Primer Amplification (SISPA) approach combined to MinION Oxford Nanopore sequencing technology. All together, these results highlight the co-circulation of a wide diversity of BTV serotypes in a quite restricted area and emphasize the need for entomological and livestock surveillance, particularly in light of recent changes in the global distribution and nature of BTV infections.

Viral diversity and blood-feeding patterns of Afrotropical Culicoides biting midges (Diptera: Ceratopogonidae)

Introduction

Culicoides biting midges (Diptera: Ceratopogonidae) are vectors of arboviral pathogens that primarily affect livestock represented by Schmallenberg virus (SBV), epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV). In Kenya, studies examining the bionomic features of Culicoides including species diversity, blood-feeding habits, and association with viruses are limited.

Methods

Adult Culicoides were surveyed using CDC light traps in two semi-arid ecologies, Baringo and Kajiado counties, in Kenya. Blood-fed specimens were analysed through polymerase chain reaction (PCR) and sequencing of cytochrome oxidase subunit 1 (cox1) barcoding region. Culicoides pools were screened for virus infection by generic RT-PCR and next-generation sequencing (NGS).

Results

Analysis of blood-fed specimens confirmed that midges had fed on cattle, goats, sheep, zebra, and birds. Cox1 barcoding of the sampled specimens revealed the presence of known vectors of BTV and epizootic hemorrhagic disease virus (EHDV) including species in the Imicola group (Culicoides imicola) and Schultzei group (C. enderleni, C. kingi, and C. chultzei). Culicoides leucostictus and a cryptic species distantly related to the Imicola group were also identified. Screening of generated pools (11,006 individuals assigned to 333 pools) by generic RT-PCR revealed presence of seven phylogenetically distinct viruses grouping in the genera Goukovirus, Pacuvirus and Orthobunyavirus. The viruses showed an overall minimum infection rate (MIR) of 7.0% (66/333, 95% confidence interval (CI) 5.5-8.9). In addition, full coding sequences of two new iflaviruses, tentatively named Oloisinyai_1 and Oloisinyai_2, were generated by next-generation sequencing (NGS) from individual homogenate of Culicoides pool.

Conclusion

The results indicate a high genetic diversity of viruses in Kenyan biting midges. Further insights into host-vector-virus interactions as well as investigations on the potential clinical significance of the detected viruses are warranted.

Recognition of Field Signs, Necropsy Procedures, and Evaluation of Macroscopic Lesions of Cervids Infected with Epizootic Hemorrhagic Disease Virus

Epizootic hemorrhagic disease virus (EHDV) is an arthropod-borne RNA virus in the genus Orbivirus, family Sedoreoviridae. Globally, seven known EHDV serotypes circulate among ruminant hosts and Culicoides species vectors. A variety of domestic and wild ruminant species are susceptible to EHDV infection, but infection outcome is highly variable between species, as well as between individuals of the same species. Thus, this disease system inherently operates at the wildlife-livestock interface. Domestic cattle are important hosts for EHDV, and while inapparent infection is the most common outcome, reports of clinical disease have increased in some parts of the world. However, fatal infection of cattle is rare. Among wildlife, white-tailed deer (Odocoileus virginianus) are highly susceptible to severe and often fatal disease. Considering the paucity of data and poorly characterized pathology of EHD in cattle, white-tailed deer represent a case study for describing the field signs and necropsy lesions associated with EHD. Here we describe the field signs that commonly define EHD outbreaks in North America, a basic approach to a gross necropsy examination of white-tailed deer, description of the gross lesions that may be present, and diagnostic sample collection. Field investigations of large-scale EHD outbreaks are common in North America. The necropsy examination is an essential tool in the study of disease and when coupled with other disciplines (e.g., virology, immunology, epidemiology) has been fundamentally important to understanding EHD in North America.

Latitudinal and anthropogenic effects on the structuring of networks linking blood-feeding flies and their vertebrate hosts

Biting flies (Diptera) transmit pathogens that cause many important diseases in humans as well as domestic and wild animals. The networks of feeding interactions linking these insects to their hosts, and how they vary geographically and in response to human land-use, are currently poorly documented but are relevant to understanding cross-species disease transmission. We compiled a database of biting Diptera-host interactions from the literature to investigate how key interaction network metrics vary latitudinally and with human land-use. Interaction evenness and H2' (a measure of the degree of network specificity) did not vary significantly with latitude. Compared to near-natural habitats, interaction evenness was significantly lower in agricultural habitats, where networks were dominated by relatively few species pairs, but there was no evidence that the presence of humans and their domesticated animals within networks led to systematic shifts in network structure. We discuss the epidemiological relevance of these results and the implications for predicting and mitigating future spill-over events.

Current Knowledge on Epizootic Haemorrhagic Disease in China

Epizootic haemorrhagic disease (EHD) is an infectious, non-contagious viral disease of ruminants caused by epizootic haemorrhagic disease virus (EHDV) and is transmitted by insects of the genus Culicoides. In 2008, EHD was listed on the World Organization for Animal Health (WOAH) list of notifiable terrestrial and aquatic animal diseases. This article reviews the distribution of EHD in China and relevant studies and proposes several suggestions for the prevention and control of EHD. There have been reports of positivity for serum antibodies against EHDV-1, EHDV-2, EHDV-5, EHDV-6, EHDV-7, EHDV-8 and EHDV-10 in China. Strains of EHDV-1, -5, -6, -7, -8 and -10 have been isolated, among which the Seg-2, Seg-3 and Seg-6 sequences of serotypes -5, -6, -7 and -10 belong to the eastern topotype. The emergence of western topotype Seg-2 in EHDV-1 strains indicates that EHDV-1 strains in China are reassortant strains of the western and eastern topotypes. A novel serotype strain of EHDV named YNDH/V079/2018 was isolated in 2018. Chinese scholars have successfully expressed the EHDV VP7 protein and developed a variety of ELISA detection methods, including antigen capture ELISA and competitive ELISA. A variety of EHDV nucleic acid detection methods, including RT-PCR and qRT-PCR, have also been developed. LAMP and the liquid chip detection technique are also available. To prevent and control EHD, several suggestions for controlling EHD transmission have been proposed based on the actual situation in China, including controlling the number of Culicoides, reducing contact between Culicoides and hosts, continued monitoring of EHDV and Culicoides in different areas of China and further development and application of basic and pioneering research related to EHD prevention and control.

An Agent-Based Model of Biting Midge Dynamics to Understand Bluetongue Outbreaks

Bluetongue (BT) is a well-known vector-borne disease that infects ruminants such as sheep, cattle, and deer with high mortality rates. Recent outbreaks in Europe highlight the importance of understanding vector-host dynamics and potential courses of action to mitigate the damage that can be done by BT. We present an agent-based model, entitled 'MidgePy', that focuses on the movement of individual Culicoides spp. biting midges and their interactions with ruminants to understand their role as vectors in BT outbreaks, especially in regions that do not regularly experience outbreaks. The results of our sensitivity analysis suggest that midge survival rate has a significant impact on the probability of a BTV outbreak as well as its severity. Using midge flight activity as a proxy for temperature, we found that an increase in environmental temperature corresponded with an increased probability of outbreak after identifying parameter regions where outbreaks are more likely to occur. This suggests that future methods to control BT spread could combine large-scale vaccination programs with biting midge population control measures such as the use of pesticides. Spatial heterogeneity in the environment is also explored to give insight on optimal farm layouts to reduce the potential for BT outbreaks.

Current Research on Infectious Diseases of Domestic Animals from a One Health Perspective

One Health is a well-known strategy for promoting and developing interdisciplinary collaboration across all aspects of health in human, animal, and environmental domains [...].

Coproduction and modeling spatial contact networks prevent bias about infectious hematopoietic necrosis virus transmission for Snake River Basin salmonids

Much remains unknown about variation in pathogen transmission across the geographic range of a free-ranging fish or animal species and about the influence of movement (associated with husbandry practices or animal behavior) on pathogen transmission. Salmonid hatcheries are an ideal system in which to study these processes. Salmonid hatcheries are managed for endangered species recovery, supplementation of threatened or at-risk fish stocks, support of fisheries, and ecosystem stability. Infectious hematopoietic necrosis virus (IHNV) is a rhabdovirus of significant concern to salmon aquaculture. Landscape IHNV transmission dynamics previously had been estimated only for salmonid hatcheries in the Lower Columbia River Basin (LCRB). The objectives of this study were to estimate IHNV transmission dynamics in a unique geographic region, the Snake River Basin (SRB), and to quantitatively estimate the effect of model coproduction on inference because previous assessments of coproduction have been qualitative. In contrast to the LCRB, the SRB has hatchery complexes consisting of a main hatchery and ≥1 satellite facility. Knowledge about hatchery complexes was held by a subset of project researchers but would not have been available to project modelers without coproduction. Project modelers generated and tested multiple versions of Bayesian susceptible-exposedinfected models to realistically represent the SRB and estimate the effect of coproduction. Models estimated the frequency of transmission routes, route-specific infection probabilities, and infection probabilities for combinations of salmonid hosts and IHNV lineages. Model results indicated that in the SRB, avoiding exposure to IHNV-positive adult salmonids is the most important action to prevent juvenile infections. Migrating adult salmonids exposed juvenile cohort-sites most frequently, and the infection probability was greatest following exposure to migrating adults. Without coproduction, the frequency of exposure by migrating adults would have been overestimated by 70 cohort-sites, and the infection probability following exposure to migrating adults would have been underestimated by∼0.09. The coproduced model had less uncertainty in the infection probability if no transmission route could be identified (Bayesian credible interval (BCI) width = 0.12) compared to the model without coproduction (BCI width = 0.34). Evidence for virus lineage MD specialization on steelhead and rainbow trout (both Oncorhynchus mykiss) was apparent without model coproduction. In the SRB, we found a greater probability of virus lineage UC infection in Chinook salmon (Oncorhynchus tshawytscha) compared to in O. mykiss, whereas in the LCRB, UC more clearly exhibited a generalist approach. Coproduction influenced estimates that depended on transmission routes, which operated differently at main hatcheries and satellite sites within hatchery complexes. Hatchery complexes are found outside of the SRB and are not specific to salmonid hatcheries alone. There is great potential for coproduction and modeling spatial contact networks to advance understanding about infectious disease transmission in complex production systems and surrounding free-ranging animal populations.

Would Climate Change Influence the Potential Distribution and Ecological Niche of Bluetongue Virus and Its Main Vector in Peru?

Bluetongue virus (BTV) is an arbovirus that is transmitted between domestic and wild ruminants by Culicoides spp. Its worldwide distribution depends on competent vectors and suitable environmental ecosystems that are becoming affected by climate change. Therefore, we evaluated whether climate change would influence the potential distribution and ecological niche of BTV and Culicoides insignis in Peru. Here, we analyzed BTV (n = 145) and C. insignis (n = 22) occurrence records under two shared socioeconomic pathway scenarios (SSP126 and SSP585) with five primary general circulation models (GCMs) using the kuenm R package v.1.1.9. Then, we obtained binary presence–absence maps and represented the risk of transmission of BTV and niche overlapping. The niche model approach showed that north and east Peru presented suitability in the current climate scenario and they would have a decreased risk of BTV, whilst its vector would be stable and expand with high agreement for the five GCMs. In addition, its niche overlap showed that the two niches almost overlap at present and would completely overlap with one another in future climate scenarios. These findings might be used to determine the areas of highest priority for entomological and virological investigations and surveillance in order to control and prevent bluetongue infections in Peru.

The Impact of Variation in the Toll-like Receptor 3 Gene on Epizootic Hemorrhagic Disease in Illinois Wild White-Tailed Deer (Odocoileus virginianus)

Epizootic hemorrhagic disease (EHD) leads to high mortality in white-tailed deer (Odocoileus virginianus) and is caused by a double-stranded RNA (dsRNA) virus. Toll-like receptor 3 (TLR3) plays a role in host immune detection and response to dsRNA viruses. We, therefore, examined the role of genetic variation within the TLR3 gene in EHD among 84 Illinois wild white-tailed deer (26 EHD-positive deer and 58 EHD-negative controls). The entire coding region of the TLR3 gene was sequenced: 2715 base pairs encoding 904 amino acids. We identified 85 haplotypes with 77 single nucleotide polymorphisms (SNPs), of which 45 were synonymous mutations and 32 were non-synonymous. Two non-synonymous SNPs differed significantly in frequency between EHD-positive and EHD-negative deer. In the EHD-positive deer, phenylalanine was relatively less likely to be encoded at codon positions 59 and 116, whereas leucine and serine (respectively) were detected less frequently in EHD-negative deer. Both amino acid substitutions were predicted to impact protein structure or function. Understanding associations between TLR3 polymorphisms and EHD provides insights into the role of host genetics in outbreaks of EHD in deer, which may allow wildlife agencies to better understand the severity of outbreaks.

Using Zoos as Sentinels for Re-Emerging Arboviruses: Vector Surveillance during an Outbreak of Epizootic Hemorrhagic Disease at the Minnesota Zoo

Vector-borne disease prevalence is increasing at a time when surveillance capacity in the United States is decreasing. One way to address this surveillance deficiency is to utilize established infrastructure, such as zoological parks, to investigate animal disease outbreaks and improve our epidemiological understanding of vector-borne pathogens. During fall 2020, an outbreak of epizootic hemorrhagic disease (EHD) at the Minnesota Zoo resulted in morbidity and seroconversion of several collection animals. In response to this outbreak, insect surveillance was conducted, and the collected insects were tested for the presence of epizootic hemorrhagic disease virus (EHDV) by RT-qPCR to better understand the local transmitting vector populations responsible for the outbreak. Six pools of Culicoides biting midges were positive for EHDV, including three pools of Culicoides sonorensis, two pools of Culicoides variipennis, and a pool of degraded C. variipennis complex midges. All three endemic serotypes of EHDV (1, 2, and 6) were detected in both animals and midge pools from the premises. Despite this outbreak, no EHDV cases had been reported in wild animals near the zoo. This highlights the importance and utility of using animal holding facilities, such as zoos, as sentinels to better understand the spatio-temporal dynamics of pathogen transmission.

Spatial epidemiology of hemorrhagic disease in Illinois wild white-tailed deer

Epizootic hemorrhagic disease (EHD) and bluetongue (BT) are vector-borne viral diseases that affect wild and domestic ruminants. Clinical signs of EHD and BT are similar; thus, the syndrome is referred to as hemorrhagic disease (HD). Syndromic surveillance and virus detection in North America reveal a northern expansion of HD. High mortalities at northern latitudes suggest recent incursions of HD viruses into northern geographic areas. We evaluated the occurrence of HD in wild Illinois white-tailed deer from 1982 to 2019. Our retrospective space-time analysis identified high-rate clusters of HD cases from 2006 to 2019. The pattern of northward expansion indicates changes in virus-host-vector interactions. Serological evidence from harvested deer revealed prior infection with BTV. However, BTV was not detected from virus isolation in dead deer sampled during outbreaks. Our findings suggest the value of capturing the precise geographic location of outbreaks, the importance of virus isolation to confirm the cause of an outbreak, and the importance of expanding HD surveillance to hunter-harvested wild white-tailed deer. Similarly, it assists in predicting future outbreaks, allowing for targeted disease and vector surveillance, helping wildlife agencies communicate with the public the cause of mortality events and viral hemorrhagic disease outcomes at local and regional scales.