Epizootic Hemorrhagic Disease Virus: Current Knowledge and Emerging Perspectives

Epizootic Hemorrhagic Disease (EHD) of ruminants is a viral pathology that has significant welfare, social, and economic implications. The causative agent, epizootic hemorrhagic disease virus (EHDV), belongs to the Orbivirus genus and leads to significant regional disease outbreaks among livestock and wildlife in North America, Asia, Africa, and Oceania, causing significant morbidity and mortality. During the past decade, this viral disease has become a real threat for countries of the Mediterranean basin, with the recent occurrence of several important outbreaks in livestock. Moreover, the European Union registered the first cases of EHDV ever detected within its territory. Competent vectors involved in viral transmission, Culicoides midges, are expanding its distribution, conceivably due to global climate change. Therefore, livestock and wild ruminants around the globe are at risk for this serious disease. This review provides an overview of current knowledge about EHDV, including changes of distribution and virulence, an examination of different animal models of disease, and a discussion about potential treatments to control the disease.

Full-genome characterisation of a putative novel serotype of Yonaguni orbivirus isolated from cattle in Yunnan province, China

In July 2019, a novel viral strain (JH2019C603) was isolated from sentinel cattle in Jinghong City, in the subtropical region of Yunnan Province, China. The virus replicated and caused cytopathological effects in both Aedes albopictus (C6/36) and Baby Hamster Syrian Kidney (BHK-21) cells. Agarose gel electrophoresis analysis revealed a viral genome comprised of 10 segments of double-stranded RNA, with a 1-2-2-1-1-1-1-1 migration pattern. Complete genome sequences of the JH2019C603 virus were determined through full-length cDNA amplification. Phylogenetic analysis based on the amino acid (aa) sequences of RNA-dependent RNA Polymerase (Pol), Major subcore (T2) and Major core-surface (T13) showed that JH2019C603 clustered with Yonaguni orbivirus (YONOV) from Japan, with aa identities relative to YONOV of 97.7% (Pol), 99.0% (T2) and 98.5% (T13). However, phylogenetic analysis based on the aa sequences of the outer capsid protein one and two (OC1 and OC2) showed that JH2019C603 formed an independent branch in the phylogenetic tree, and its aa identity with YONOV was only 55.4% (OC1) and 80.8% (OC2), respectively. Compared with the prototype of YONOV, a notable sequence deletion was observed in the 3' non-coding region of NS1, with the NS1 of JH2019C603 encoded within segment 7 (Seg-7), in contrast to YONOV, which contains NS1 in Seg-6. These results indicate that JH2019C603 belongs to the YONOV lineage and might be a novel serotype or a highly variant strain of YONOV. These findings will facilitate the identification of new isolates and clarify their geographical distribution, epidemiology, genetic diversity and possible disease associations.

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.

Perspectives on the Changing Landscape of Epizootic Hemorrhagic Disease Virus Control

Epizootic hemorrhagic disease (EHD) is an insect-transmitted viral disease of wild and domestic ruminants. It was first described following a 1955 epizootic in North American white-tailed deer (Odocoileus virginianus), a species which is highly susceptible to the causative agent of EHD, epizootic hemorrhagic disease virus (EHDV). EHDV has been detected globally across tropical and temperate regions, largely corresponding to the presence of Culicoides spp. biting midges which transmit the virus between ruminant hosts. It regularly causes high morbidity and mortality in wild and captive deer populations in endemic areas during epizootics. Although cattle historically have been less susceptible to EHDV, reports of clinical disease in cattle have increased in the past two decades. There is a pressing need to identify new methods to prevent and mitigate outbreaks and reduce the considerable impacts of EHDV on livestock and wildlife. This review discusses recent research advancements towards the control of EHDV, including the development of new investigative tools and progress in basic and applied research focused on virus detection, disease mitigation, and vector control. The potential impacts and implications of these advancements on EHD management are also discussed.

Evaluation of 2012 US EHDV-2 outbreak isolates for genetic determinants of cattle infection

Following a summer of severe drought and abnormally high temperatures, a major outbreak of EHDV occurred during 2012 in the USA. Although EHDV-1, -2 and -6 were isolated, EHDV-2 was the predominant virus serotype detected during the outbreak. In addition to large losses of white-tailed deer, the Midwest and northern Plains saw a significant amount of clinical disease in cattle. Phylogenetic analyses and sequence comparisons of newly sequenced whole genomes of 2012 EHDV-2 cattle isolates demonstrated that eight of ten EHDV-2 genomic segments show no genetic changes that separate the cattle outbreak sequences from other EHDV-2 isolates. Two segments, VP2 and VP6, did show several unique genetic changes specific to the 2012 cattle outbreak isolates, although the impact of the genetic changes on viral fitness is unknown. The placement of isolates from 2007 and 2011 as sister group to the outbreak isolates, and the similarity between cattle and deer isolates, point to environmental variables as having a greater influence on the severity of the 2012 EHDV outbreak than viral genetic changes.

Identification and characterization of epizootic hemorrhagic disease virus serotype 6 in cattle co-infected with bluetongue virus in Trinidad, West Indies

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Epizootic haemorrhagic disease virus serotype 6 (EHDV-6) is circulating in Trinidad.

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EHDV is infecting cattle at a slower rate than BTV.

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EHDV appears to have a faster viral evolution rate than BTV.

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The EHDV-6 Trinidad strain (VP-2) falls within the eastern topotype clade that is likely to have originated from Australia.

Epizootic hemorrhagic disease virus (EHDV) is an economically important virus that can cause severe clinical disease in deer and to a lesser extent cattle. This study set out to determine and characterize which EHDV serotypes were circulating in Trinidad. Serum and whole blood samples were collected monthly for six months from a cohort of cattle imported to Trinidad from the USA. Results revealed that all the cattle seroconverted to EHDV within six months of their arrival, with EHDV RNA being detected in the samples just prior to antibodies, as expected. Serotyping assays revealed that a single serotype (EHDV-6) was circulating in the cattle. Sequencing of the surface viral protein (VP2) of EHDV-6, followed by phylogenetic analysis, revealed that the Trinidad EHDV-6 strain was closely related to EHDV-6 viruses found in Guadeloupe (2010), Martinique (2010) and USA (2006), with 96–97.2% nucleotide identity. The Trinidad EHDV-6 VP-2 shared 97.2% identity with the Australian EHDV-6 prototype strain, classifying it within the eastern topotype clade. Bayesian coalescent analysis support Australia as the most probable source for the EHDV-6 VP2 sequences in the Americas and Caribbean region and suggests that the they diverged from the Australian prototype strain around 1966 (95% HPD 1941–1979).

Generation of virus like particles for epizootic hemorrhagic disease virus

Epizootic hemorrhagic disease virus (EHDV) is a distinct species within the genus Orbivirus, within the family Reoviridae. The epizootic hemorrhagic disease virus genome comprises ten segments of linear, double stranded (ds) RNA, which are packaged within each virus particle. The EHDV virion has a three layered capsid-structure, generated by four major viral proteins: VP2 and VP5 (outer capsid layer); VP7 (intermediate, core-surface layer) and VP3 (innermost, sub-core layer). Although EHDV infects cattle sporadically, several outbreaks have recently occurred in this species in five Mediterranean countries, indicating a potential threat to the European cattle industry. EHDV is transmitted by biting midges of the genus Culicoides, which can travel long distances through wind-born movements (particularly over water), increasing the potential for viral spread in new areas/countries. Expression systems to generate self-assembled virus like particles (VLPs) by simultaneous expression of the major capsid-proteins, have been established for several viruses (including bluetongue virus). This study has developed expression systems for production of EHDV VLPs, for use as non-infectious antigens in both vaccinology and serology studies, avoiding the risk of genetic reassortment between vaccine and field strains and facilitating large scale antigen production. Genes encoding the four major-capsid proteins of a field strain of EHDV-6, were isolated and cloned into transfer vectors, to generate two recombinant baculoviruses. The expression of these viral genes was assessed in insect cells by monitoring the presence of specific viral mRNAs and by western blotting. Electron microscopy studies confirmed the formation and purification of assembled VLPs.