Epizootic hemorrhagic disease virus serotype 6 experimentation on adult cattle

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.

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 a commercial ELISA for detection of epizootic haemorrhagic disease antibodies in domestic and wild ruminant sera

Bluetongue (BT) and epizootic haemorrhagic disease (EHD) are vector-borne viral diseases affecting domestic and wild ruminants. Both are notifiable under OIE rules. BT and EHD viruses (BTV and EHDV) are closely related Orbiviruses with structural, antigenic and molecular similarities. Both viruses can produce analogous clinical signs in susceptible animals. Serological tests are commonly used for BT and EHD diagnosis and surveillance. Competitive ELISA (c-ELISA) is the most widely used serological test for the specific detection of BTV or EHDV viral protein 7 (VP7) antibodies (Abs). The specificity and sensitivity of the BTV c-ELISA kits available on the market are recognized for the detection of BTV Abs. Concerning EHD, a single commercial EHDV c-ELISA kit (ELISA A kit) commonly used for diagnosis in Europe and Africa was available between 2011 and 2018 but is now no longer on the market. In this study, we evaluated a new commercial c-ELISA to detect ruminant EHDV VP7 Abs in 2,199 serum samples from cattle, sheep, goats, wild deer and zoo animals. The results showed that this ELISA kit is specific and can detect the presence of IgG anti-EHDV VP7 with a very good diagnostic specificity and a satisfactory sensitivity in domestic ruminants, zoo animals and wild deer. Therefore, the evaluated c-ELISA can detect the introduction of EHDV into an area where BTV-seropositive domestic animals are present. The performance of this kit is similar to that of the c-ELISA A kit and can thus be used for diagnosis.

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.

First molecular and serological detection of Epizootic Hemorrhagic Disease virus in white tailed deer ( Odocoileus virginianus ) from Tamaulipas, Mexico

ABSTRACT Epizootic hemorrhagic disease viruses (EHDV) are dsRNA arboviruses transmitted by biting midges of the genus Culicoides that cause disease in domestic and wild ruminants. Epizootic hemorrhagic disease (EHD) is considered the most important infectious disease of white tailed deer (WTD) in North America, some studies in Northeast Mexico reported EHDV-seropositive WTD and EHDV-infected Culicoides vectors. The increasing population of WTD that share habitat with livestock in Northeast México highlights the importance of EHD for the livestock industry in the transboundary region with the U.S. One hundred and twenty two samples from WTD in Tamaulipas state, Mexico were tested by ELISA and RT-PCR for EHDV antibodies and nucleic acid, respectively. Twelve animals were seropositive to ELISA and eleven animals were positive by RT-PCR. This is the first report of EHDV nucleic acid detection in WTD from Mexico. It is hypothesized that applying the transboundary disease approach to interdisciplinary research will help fill knowledge gaps, which could help develop countermeasures to mitigate the threat of EHDV infection in wildlife and livestock along the U.S.-Mexico border.

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

•

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

•

EHDV is infecting cattle at a slower rate than BTV.

•

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

•

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).

Evaluation of an IGM-specific ELISA for early detection of bluetongue virus infections in domestic ruminants sera

Competitive-ELISA (c-ELISA) is the most widely used serological test for the detection of Bluetongue virus (BTV) viral protein 7 (VP7) antibodies (Ab). However, these BTV c-ELISAs cannot to distinguish between IgG and IgM. IgM Ab are generated shortly after the primary immune response against an infectious agent, indicating a recent infection or exposure to antigens, such as after vaccination. Because the BTV genome or anti-VP7 Ab can be detected in ruminant blood months after infection, BTV diagnostic tools cannot discriminate between recent and old infections. In this study, we evaluated an IgM-capture ELISA prototype to detect ruminant anti-BTV VP7 IgM on 1,650 serum samples from cattle, sheep, or goats. Animals were BTV-naive, infected, or/and vaccinated with BTV-1, -2, -4, -8, -9, -16, or -27, and we also included 30 sera from cattle infected with the Epizootic haemorrhagic disease virus (EHDV) serotype 6. Results demonstrated that this ELISA kit is specific and can detect the presence of IgM with satisfactory diagnostic specificity and sensitivity from 1 to 5 weeks after BTV infection in domestic ruminants (for goats and cattle; for sheep, at least up to 24 days). The peak of anti-VP7 IgM was reached when the level of infectious viruses and BTV RNA in blood were the highest. The possibility of detecting BTV-RNA in IgM-positive sera allows the amplification and sequencing of the partial RNA segment 2 (encoding the serotype specific to VP2) to determine the causative BTV serotype/strain. Therefore, BTV IgM ELISA can detect the introduction of BTV (or EHDV) in an area with BTV-seropositive domestic animals regardless of their serological BTV status. This approach may also be of particular interest for retrospective epidemiological studies on frozen serum samples.

Cross-species transmission potential between wild pigs, livestock, poultry, wildlife, and humans: implications for disease risk management in North America

Cross-species disease transmission between wildlife, domestic animals and humans is an increasing threat to public and veterinary health. Wild pigs are increasingly a potential veterinary and public health threat. Here we investigate 84 pathogens and the host species most at risk for transmission with wild pigs using a network approach. We assess the risk to agricultural and human health by evaluating the status of these pathogens and the co-occurrence of wild pigs, agriculture and humans. We identified 34 (87%) OIE listed swine pathogens that cause clinical disease in livestock, poultry, wildlife, and humans. On average 73% of bacterial, 39% of viral, and 63% of parasitic pathogens caused clinical disease in other species. Non-porcine livestock in the family Bovidae shared the most pathogens with swine (82%). Only 49% of currently listed OIE domestic swine diseases had published wild pig surveillance studies. The co-occurrence of wild pigs and farms increased annually at a rate of 1.2% with as much as 57% of all farms and 77% of all agricultural animals co-occurring with wild pigs. The increasing co-occurrence of wild pigs with livestock and humans along with the large number of pathogens shared is a growing risk for cross-species transmission.

Novel serotype of bluetongue virus in South America and first report of epizootic haemorrhagic disease virus in Ecuador

Bluetongue virus (BTV) and Epizootic haemorrhagic disease virus (EHDV) are closely related Orbiviruses that affect domestic and wild ruminants. In Ecuador previous serological studies reported the presence of BTV; however, no data are available about the presence of EHDV. In this study, 295 cattle without symptoms of infection were sampled from two farms located in Andean and Amazonian regions and from a slaughterhouse in the coastal region. ELISA analyses showed high prevalence of BTV (98.9%) and EHDV (81.3%) antibodies, and RT-qPCRs revealed the presence of EHDV (24.1%) and BTV (10.2%) genomes in cattle blood samples. Viral isolation allowed to identify EHDV serotype 1 (EHDV1) and BTV serotypes 9 (BTV9), 13 and 18. These findings suggest that BTV and EHDV are enzootic diseases in Ecuador.

Development of a Double-Antigen Microsphere Immunoassay for Simultaneous Group and Serotype Detection of Bluetongue Virus Antibodies

Bluetongue viruses (BTV) are arboviruses responsible for infections in ruminants. The confirmation of BTV infections is based on rapid serological tests such as enzyme-linked immunosorbent assays (ELISAs) using the BTV viral protein 7 (VP7) as antigen. The determination of the BTV serotype by serological analyses could be only performed by neutralization tests (VNT) which are time-consuming and require BSL3 facilities. VP2 protein is considered the major serotype-defining protein of BTV. To improve the serological characterization of BTV infections, the recombinant VP7 and BTV serotype 8 (BTV-8) VP2 were synthesized using insect cells expression system. The purified antigens were covalently bound to fluorescent beads and then assayed with 822 characterized ruminant sera from BTV vaccinations or infections in a duplex microsphere immunoassay (MIA). The revelation step of this serological duplex assay was performed with biotinylated antigens instead of antispecies conjugates to use it on different ruminant species. The results demonstrated that MIA detected the anti-VP7 antibodies with a high specificity as well as a competitive ELISA approved for BTV diagnosis, with a better efficiency for the early detection of the anti-VP7 antibodies. The VP2 MIA results showed that this technology is also an alternative to VNT for BTV diagnosis. Comparisons between the VP2 MIA and VNT results showed that VNT detects the anti-VP2 antibodies in an early stage and that the VP2 MIA is as specific as VNT. This novel immunoassay provides a platform for developing multiplex assays, in which the presence of antibodies against multiple BTV serotypes can be detected simultaneously.

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.

Development of Real-Time RT-PCR Assays for Detection and Typing of Epizootic Haemorrhagic Disease Virus

Epizootic haemorrhagic disease virus (EHDV) is an emerging arboviral pathogen of wild and domestic ruminants worldwide. It is closely related to bluetongue virus (BTV) and is transmitted by adult females of competent Culicoides vector species. The EHDV genome consists of ten linear double‐stranded (ds)RNA segments, encoding five non‐structural and seven structural proteins. Genome‐segment reassortment contributes to a high level of genetic variation in individual virus strains, particularly in the areas where multiple and distinct virus lineages co‐circulate. In spite of the relatively close relationship between BTV and EHDV herd‐immunity to BTV does not appear to protect against the introduction and infection of animals by EHDV. Although EHDV can cause up to 80% morbidity in affected animals, vaccination with the homologous EHDV serotype is protective. Outer‐capsid protein VP2, encoded by Seg‐2, is the most variable of the EHDV proteins and determines both the specificity of reactions with neutralizing antibodies and consequently the identity of the eight EHDV serotypes. In contrast, VP6 (the viral helicase), encoded by Seg‐9, is highly conserved, representing a virus species/serogroup‐specific antigen. We report the development and evaluation of quantitative (q)RT‐PCR assays targeting EHDV Seg‐9 that can detect all EHDV strains (regardless of geographic origin/topotype/serotype), as well as type‐specific assays targeting Seg‐2 of the eight EHDV serotypes. The assays were evaluated using orbivirus isolates from the ‘Orbivirus reference collection’ (ORC) at The Pirbright Institute and were shown to be EHDV pan‐reactive or type‐specific. They can be used for rapid, sensitive and reliable detection and identification (typing) of EHDV RNA from infected blood, tissue samples, homogenized Culicoides, or tissue culture supernatant. None of the assays detected RNA from closely related but heterologous orbiviruses, or from uninfected host animals or cell cultures. The techniques presented could be used for both surveillance and vaccine matching (serotype identification) as part of control strategies for incursions in wild and domestic animal species.

Host and Potential Vector Susceptibility to an Emerging Orbivirus in the United States

Epizootic hemorrhagic disease viruses (EHDVs) are orbiviruses transmitted by Culicoides biting midges to domestic and wild ruminants. EHDV-1 and EHDV-2 are endemic in the United States, where epizootic hemorrhagic disease is the most significant viral disease of white-tailed deer (WTD; Odocoileus virginianus) and reports of epizootic hemorrhagic disease in cattle are increasing. In 2006, a reassortant EHDV-6 was isolated from dead WTD in Indiana and has been detected each subsequent year over a wide geographic region. Since EHDV-6 is not a historically endemic serotype in the United States, it is important to understand infection outcome in potential hosts. Specifically, we aimed to evaluate the pathogenicity of the virus in 2 primary US ruminant hosts (WTD and cattle) and the susceptibility of a confirmed US vector ( Culicoides sonorensis). Five WTD and 4 cattle were inoculated with >106 TCID50 EHDV-6 by intradermal and subcutaneous injection. All 5 WTD exhibited moderate to severe disease, and 3 died. Viremia was first detected 3 to 5 days postinfection (dpi) with surviving animals seroconverting by 10 dpi. Two of 4 inoculated cattle had detectable viremia, 5 to 10 dpi and 7 to 24 dpi, respectively. No clinical, hematologic, or pathologic abnormalities were observed. Antibodies were detected by 10 dpi in 3 of 4 cows. C. sonorensis were fed on WTD blood spiked with EHDV-6 and held for 4 to 14 days postfeeding at 25°C. From 4 to 14 days postfeeding, 19 of 171 midges were virus isolation positive and 6 of 171 had ≥102.7 TCID50 EHDV-6. Although outcomes varied, these studies demonstrate the susceptibility of ruminant and vector hosts in the United States for this recently emerged EHDV serotype.

Development of a competitive ELISA for NS3 antibodies as DIVA test accompanying the novel Disabled Infectious Single Animal (DISA) vaccine for Bluetongue

Recently, we have developed a novel vaccine for Bluetongue named BT Disabled Infectious Single Animal (DISA) vaccine. Due to the lack of non-essential NS3/NS3a protein, BT DISA vaccine is a replicating vaccine, but without the inherent risks of live-attenuated vaccines, such as residual virulence or reversion to virulence by mutations, reassortment with field virus, horizontal spread by vectors and vertical transmission. The immune response induced by BT DISA vaccines is rapidly induced, highly protective and serotype specific which is dependent on the immunodominant and serotype determining VP2 protein. The BT DISA vaccine platform provides the replacement of exclusively VP2 from different serotypes in order to safely formulate multivalent cocktail vaccines. The lack of NS3/NS3a directed antibodies by BT DISA vaccination enables differentiation of infected from vaccinated animals (DIVA principle). A highly conserved immunogenic site corresponding to the late domain was mapped in the N-terminal region of NS3. We here established an NS3-specific competitive ELISA (NS3 cELISA) as serological DIVA test accompanying BT DISA vaccines. To this end, NS3 protein missing putative transmembrane regions was produced in large amounts in bacteria and used as antigen in the NS3 cELISA which was investigated with a variety of sera. The NS3 cELISA displayed a high sensitivity and specificity similar to the commercially available VP7-specific cELISA. Results of previously performed vaccination-challenge trials with BT DISA vaccines clearly demonstrate the DIVA system based on the NS3 cELISA and BT vaccine free of NS3 protein.

Duplex Real-Time RT-PCR Assays for the Detection and Typing of Epizootic Haemorrhagic Disease Virus

Epizootic haemorrhagic disease virus (EHDV) may cause severe clinical episodes in some species of deer and sometimes in cattle. Laboratory diagnosis provides a basis for the design and timely implementation of disease control measures. There are seven distinct EHDV serotypes, VP2 coding segment 2 being the target for serotype specificity. This paper reports the development and validation of eight duplex real-time RT-PCR assays to simultaneously amplify the EHDV target (S9 for the pan-EHDV real-time RT-PCR assay and S2 for the serotyping assays) and endogenous control gene Beta-actin. Analytical and diagnostic sensitivity and specificity, inter- and intra-assay variation and efficiency were evaluated for each assay. All were shown to be highly specific and sensitive.