Development of a nested-PCR test based on sequence analysis of epizootic hemorrhagic disease viruses non-structural protein 1 (NS1)

End-Point RT-PCR Assays for Detection and Typing of Epizootic Hemorrhagic Disease Virus

The emergence of EHDV in Europe during the autumn of 2022 reinforces the need for molecular tools (RT-PCR) for rapid detection of animals infected with this virus. Viral genome testing can be performed on whole blood under anticoagulant, spleen, and bloody organ homogenates from ruminants. It can also be performed on cell culture following viral isolation tests. Various so-called classical or end-point RT-PCRs will be described, which permit the amplification of a part of the viral genome (targeting segment 7) allowing the detection of EHDV whatever the serotype (pan-RT-PCR) and also to amplify a portion of the gene coding the viral protein (VP) 2 enabling serotyping. The PCR amplification products are visualized by agarose gel electrophoresis. Sequencing of the type-specific RT-PCR amplification products allows for the serotype of the virus to be determined.

Diagnostic Tools for Bluetongue and Epizootic Hemorrhagic Disease Viruses Applicable to North American Veterinary Diagnosticians

This review provides an overview of current and potential new diagnostic tests for bluetongue (BT) and epizootic hemorrhagic disease (EHD) viruses compiled from international participants of the Orbivirus Gap Analysis Workshop, Diagnostic Group. The emphasis of this review is on diagnostic tools available to North American veterinary diagnosticians. Standard diagnostic tests are readily available for BT/EHD viruses, and there are described tests that are published in the World Organization for Animal Health (OIE) Terrestrial Manual. There is however considerable variation in the diagnostic approach to these viruses. Serological assays are well established, and many laboratories are experienced in running these assays. Numerous nucleic acid amplification assays are also available for BT virus (BTV) and EHD virus (EHDV). Although there is considerable experience with BTV reverse-transcriptase PCR (RT-PCR), there are no standards or comparisons of the protocols used by various state and federal veterinary diagnostic laboratories. Methods for genotyping BTV and EHDV isolates are available and are valuable tools for monitoring and analyzing circulating viruses. These methods include RT-PCR panels or arrays, RT-PCR and sequencing of specific genome segments, or the use of next-generation sequencing. In addition to enabling virus characterization, use of advanced molecular detection methods, including DNA microarrays and next-generation sequencing, significantly enhance the ability to detect unique virus strains that may arise through genetic drift, recombination, or viral genome segment reassortment, as well as incursions of new virus strains from other geographical areas.

Genetic characterization of epizootic hemorrhagic disease virus strains isolated from cattle in Israel

Epizootic hemorrhagic disease virus (EHDV), a member of the genus Orbivirus not reported previously in Israel, was isolated from Israeli cattle during a 'bluetongue-like' disease outbreak in 2006. To ascertain the origin of this new virus, three isolates from the outbreak were fully sequenced and compared with available sequences. Whilst the L2 gene segment clustered with the Australian EHDV serotype 7 (EHDV-7) reference strain, most of the other segments were clustered with EHDV isolates of African/Middle East origin, specifically Bahrain, Nigeria and South Africa. The M6 gene had genetic relatedness to the Australian/Asian strains, but with the limited data available the significance of this relationship is unclear. Only one EHDV-7 L2 sequence was available, and as this gene encodes the serotype-specific epitope, the relationship of these EHDV-7 L2 genes to an Australian EHDV-7 reflects the serotype association, not necessarily the origin. The genetic data indicated that the strains affecting Israel in 2006 may have been related to similar outbreaks that occurred in North Africa in the same year. This finding also supports the hypothesis that EHDV entered Israel during 2006 and was not present there before this outbreak.

Development and performance evaluation of a streamlined method for nucleic acid purification, denaturation, and multiplex detection of Bluetongue virus and Epizootic hemorrhagic disease virus

Bluetongue virus (BTV) and Epizootic hemorrhagic disease virus (EHDV) possess similar structural and molecular features, are transmitted by biting midges (genus Culicoides), and cause similar diseases in some susceptible ruminants. Generally, BTV causes subclinical disease in cattle, characterized by a prolonged viremia. EHDV-associated disease in cattle is less prominent; however, it has emerged as a major economic threat to the white-tailed deer (Odocoileus virginianus) industry in many areas of the United States. The recent emergence of multiple BTV and EHDV serotypes previously undetected in the United States demonstrates the need for robust detection of all known serotypes and differential diagnosis. For this purpose, a streamlined workflow consisting of an automated nucleic acid purification and denaturation method and a multiplex one-step reverse transcription quantitative polymerase chain reaction for the simultaneous detection of BTV serotypes 1-24 and EHDV serotypes 1-7 was developed using previously published BTV and EHDV assays. The denaturation of double-stranded (ds) BTV and EHDV RNA was incorporated into the automated nucleic acid purification process thus eliminating the commonly used separate step of dsRNA denaturation. The performance of this workflow was compared with the World Organization of Animal Health BTV reference laboratory (National Veterinary Services Laboratory, Ames, Iowa) workflow for BTV and EHDV detection, and high agreement was observed. Implementation of the workflow in routine diagnostic testing enables the detection of, and differentiation between, BTV and EHDV, and coinfections in bovine blood and cervine tissues, offering significant benefits in terms of differential disease diagnosis, herd health monitoring, and regulated testing.

Epizootic hemorrhagic disease in yaks (Bos grunniens)

An epizootic of hemorrhagic disease associated with Epizootic hemorrhagic disease virus serotype 2 (EHDV-2) infections in yaks from 5 herds occurred in Colorado between August 21 and October 3, 2012. Affected yaks presented with fever, lethargy, anorexia, dyspnea, and swollen conjunctivae. Ulcerated dental pads, mucoid sanguineous nasal discharge, petechial hemorrhages in multiple organs, pulmonary edema, and serosanguinous fluid in the thorax, abdomen, and pericardial sac were observed at necropsy. Blood and tissue samples from 8 yaks with similar clinical signs and necropsy findings were positive for EHDV-2 by reverse transcription polymerase chain reaction and 5 yaks were seropositive for EHDV. Tests for malignant catarrhal fever ( Ovine herpesvirus 2), Bovine viral diarrhea virus, Bovine herpesvirus 1, Foot-and-mouth disease virus, and Vesicular stomatitis virus were negative. The findings indicate that yaks are susceptible to infection with EHDV-2 and exhibit the clinical signs, and gross and histologic lesions of hemorrhagic disease observed in other ruminant species.

Epizootic heamorragic disease

Epizootic haemorrhagic disease (EHD) is an infectious non-contagious viral disease transmitted by insects of the genus Culicoides which affects wild and domestic ruminants. The causative agent, the epizootic haemorrhagic disease virus (EHDV), belongs to the family Reoviridae, genus Orbivirus and shares many morphological and structural characteristics with the other members of the genus such as bluetongue, African horse sickness and equine encephalosis viruses. In recent years EHD outbreaks have been reported in countries bordering the European Union. They caused disease in cattle and severe repercussion on the livestock industry of the affected countries. In the light of recent European bluetongue epizootic these events pose an increasing threat to the European Union. This review includes the most recent information regarding the virus and the disease as well as tools for its diagnosis and control. It is our conviction that more attention should be drawn to both EHDV and the disease itself in order to fulfil all these gaps and not to be unprepared in case future possible incursions.

RT-PCR assays for seven serotypes of epizootic haemorrhagic disease virus & their use to type strains from the Mediterranean region and North America

Epizootic haemorrhagic disease virus (EHDV) infects wild ruminants, causing a frequently fatal haemorrhagic disease. However, it can also cause bluetongue-like disease in cattle, involving significant levels of morbidity and mortality, highlighting a need for more rapid and reliable diagnostic assays. EHDV outer-capsid protein VP2 (encoded by genome-segment 2 [Seg-2]) is highly variable and represents the primary target for neutralising antibodies generated by the mammalian host. Consequently VP2 is also the primary determinant of virus "serotype", as identified in virus neutralisation tests (VNT). Although previous reports have indicated eight to ten EHDV serotypes, recent serological comparisons and molecular analyses of Seg-2 indicate only seven EHDV "types". Oligonucleotide primers were developed targeting Seg-2, for use in conventional RT-PCR assays to detect and identify these seven types. These assays, which are more rapid and sensitive, still show complete agreement with VNT and were used to identify recent EHDV isolates from the Mediterranean region and North America.

An improved real-time polymerase chain reaction for the simultaneous detection of all serotypes of Epizootic hemorrhagic disease virus

Epizootic hemorrhagic disease virus (EHDV) is a significant pathogen of wild and sometimes domestic ungulates worldwide. Rapid and reliable methods for virus detection and identification play an essential part in the control of epizootic hemorrhagic disease (EHD). In the present study, a 1-step real-time polymerase chain reaction (PCR) group-specific assay was developed. The assay detects genome segment 5 (NS1) from all of the 8 serotypes of EHDV. Assay sensitivity was evaluated relative to a conventional gel-based nested PCR using cell culture-derived virus and diagnostic samples from clinically affected white-tailed deer (Odocoileus virginianus). The assay reliably amplified the NS1 gene from any of the EHDV strains tested, including isolates from each of the 8 EHDV serotypes. No cross-reactions were detected when all 24 serotypes of Bluetongue virus, a closely related member of the genus Orbivirus, were tested. A panel of 76 known EHDV-positive clinical samples was used to compare the performance of the assay relative to a previously reported real-time PCR assay. Results indicated that there was no statistically significant difference between the threshold cycle values obtained with both assays. A collection of 178 diagnostic samples submitted for EHD diagnosis was also used for test evaluation. The assay could be applied for rapid detection of EHDV in clinical samples from susceptible ruminants during an outbreak of the disease. In addition, this PCR assay has the benefits of being reliable and simple and could provide a valuable tool for studying the epidemiology of EHDV infection in susceptible ruminants by facilitating the detection of EHDV, regardless of the serotype.

A multiplex real-time reverse transcription polymerase chain reaction assay for detection and differentiation of Bluetongue virus and Epizootic hemorrhagic disease virus serogroups

Bluetongue virus (BTV) causes disease in domestic and wild ruminants and results in significant economic loss. The closely related Epizootic hemorrhagic disease virus (EHDV) has been associated with bluetongue-like disease in cattle. Although U.S. EHDV strains have not been experimentally proven to cause disease in cattle, there is serologic evidence of infection in cattle. Therefore, rapid diagnosis and differentiation of BTV and EHDV is required. The genetic sequence information and bioinformatic analysis necessary to design a real-time reverse transcription polymerase chain reaction (RT-PCR) assay for the early detection of indigenous and exotic BTV and EHDV is described. This sequence data foundation focused on 2 conserved target genes: one that is highly expressed in infected mammalian cells, and the other is highly expressed in infected insect cells. The analysis of all BTV and EHDV prototype strains indicated that a complex primer design was necessary for both a virus group-comprehensive and virus group-specific gene amplification diagnostic test. This information has been used as the basis for the development of a rapid multiplex BTV-EHDV real-time RT-PCR that detects all known serotypes of both viruses and distinguishes between BTV and EHDV serogroups. The sensitivity of this rapid, single-tube, real-time RT-PCR assay is sufficient for diagnostic application, without the contamination problems associated with standard gel-based RT-PCR, especially nested RT-PCR tests.

Bluetongue virus serotype 17 sequence variation associated with neutralization

Bluetongue virus (BTV) is an insect-transmitted orbivirus of importance to the cattle and sheep industry. The VP2 protein, encoded by L2, contains neutralizing epitopes. Previously, a panel of neutralizing monoclonal antibodies (MAbs) to the BTV serotype 17 (BTV-17) prototype strain was generated and it was determined that the neutralization domain consists of three overlapping epitopes. Over 30 amino acid changes were found between a neutralized BTV-17 prototype strain and a non-neutralized BTV-17 198 strain. In this study, the L2 genes from eight additional strains, representing both the neutralized and non-neutralized groups of BTV-17, were sequenced to determine the degree of conservation of the previously characterized differences. Comparison of the deduced amino acid sequences showed that 91% (30/33) of the previously noted changes were conserved within each group. The sequence of the M5 gene that encodes VP5 was also examined, since this surface protein has also been shown to affect neutralization. No consistent changes were noted between the neutralized and non-neutralized groups of BTV-17 by analysis of the VP5 protein. Finally, the L2 sequences of five MAb neutralization escape mutants were determined to identify specific amino acids involved in neutralization and perhaps virulence. All five mutants contained 1-3 amino acid changes that were in close proximity to a previously described variable region. These amino acid changes likely define critical sites in the overlapping neutralization domains previously described. This is the first description of two BT virus populations that have distinct neutralization characteristics co-circulating in a defined geographical region.

Detection of All Eight Serotypes of Epizootic Hemorrhagic Disease Virus by Real-Time Reverse Transcription Polymerase Chain Reaction

Epizootic hemorrhagic disease virus (EHDV) has been associated with bluetongue-like disease in cattle. Although U.S. EHDV strains have not been experimentally proven to cause disease in cattle, there is serologic evidence of infection. Differentiation of Bluetongue virus (BTV) and EHDV is necessary because diagnosis of infection caused by these viruses is often confused. The previously developed nested reverse transcription polymerase chain reaction (nRT-PCR) test for indigenous EHDV disease is sensitive and specific, but it is prone to contamination problems. Additionally, the EHDV nRT-PCR only detects 7 of the 8 serotypes. To develop an improved diagnostic test, sequence analysis was performed on 2 conserved target genes; one is highly expressed in infected mammalian cells, whereas the other is highly expressed in infected insect cells. This information was used to develop a rapid EHDV real-time PCR that detects all 8 EHDV serotypes. The EHDV assay did not cross-react with BTV strains and performed similarly to the nRT-PCR tests with archived clinical samples. In addition, it is superior to the nRT-PCR, not only because it is a closed system with fewer cross-contamination problems, but also because it detects all 8 serotypes and is less labor and time intensive.

Culicoides mohave (Diptera: Ceratopogonidae): new occurrence records and potential role in transmission of hemorrhagic disease

Biting midges of the genus Culicoides are important in the transmission of viral diseases affecting wild and domestic ungulates, including bluetongue (BLU) and epizootic hemorrhagic disease (EHD). The primary known vector for these viruses is C. sonorensis Wirth & Jones, however, it has been speculated that other species of Culicoides may also be involved. One potential candidate is C. mohave, a poorly studied species found in inland desert areas of the southwestern United States. In 2000 and 2001, we collected C. mohave and C. sonorensis at six sites in a previously unsurveyed area in the Sonoran Desert of southwestern Arizona and used PCR to detect nucleic acids associated with BLU and EHD viruses. C. mohave was abundant at two low-elevation sites on the study area, but uncommon or absent elsewhere. C. sonorensis commonly occurred along with C. mohave at one site, but was much less abundant. All C. mohave pools were negative for BLU viral RNA, however, 35% yielded positive results for EHD. All C. sonorensis were negative for both BLU and EHD. Our results suggest that C. mohave is a potential vector of EHD virus in this area, however additional studies are needed to determine its ability to transmit EHD.

Validation of a reverse transcriptase multiplex PCR test for the serotype determination of U.S. isolates of bluetongue virus

Bluetongue (BT) is an arthropod-borne viral disease affecting ruminants primarily in tropical and temperate regions of the world. Of the 24 serotypes of BT virus (BTV) identified worldwide, five have been found in the United States. Serotype identification of BTV isolates is important to the epidemiology of the virus, but current methods are cumbersome. A single-tube multiplex reverse transcriptase polymerase chain reaction (mRT-PCR) assay, previously developed for the serotype determination of U.S. BTV isolates, was evaluated. The determination of serotype was based on the size of the resultant amplified product. The procedure was evaluated using all 24 serotypes of BTV and nine serotypes of epizootic hemorrhagic disease virus (EHDV), a closely related orbivirus. Only the five U.S. serotypes of BTV were detected by the mRT-PCR. The assay was further tested using 132 BTV isolates originating from 24 western and southern states of the United States, from several different host species, spanning a period of 24 years. The serotypes of the isolates were determined by both a virus neutralization (VN) procedure and the mRT-PCR. Comparison of the mRT-PCR to the standard VN showed that the mRT-PCR successfully identified the serotypes of 130 of the isolates and was shown to be more reliable and specific than the VN assay.

Phylogenetic relationships of bluetongue viruses based on gene S7

Previous phylogenetic analyses based on bluetongue virus (BTV) gene segment L3, which encodes the inner core protein, VP3, indicated a geographical distribution of different genotypes. The inner core protein, VP7, of BTV has been identified as a viral attachment protein for insect cell infection. Because the inner core proteins are involved with infectivity of insect cells, we hypothesized that certain VP7 protein sequences are preferred by the insect vector species present in specific geographic locations. We compared the gene segment S7, which encodes VP7, from 39 strains of BTV isolated from Central America, the Caribbean Basin, the United States, South Africa and Australia. For comparison, the S7 sequences from strains of the related orbiviruses, epizootic hemorrhagic disease virus (EHDV) and African horse sickness virus (AHSV) were included. The S7 gene was highly conserved among BTV strains and fairly conserved among the other orbiviruses examined. VP7 sequence alignment suggests that the BTV receptor-binding site in the insect is also conserved. Phylogenetic analyses revealed that the BTV S7 nucleotide sequences do not unequivocally display geographic distribution. The BTV strains can be separated into five clades based on the deduced VP7 amino acid sequence alignment and phylogeny but evidence for preferential selection by available gnat species for a particular VP7 clade is inconclusive. Differences between clades indicate allowable variation of the VP7 binding protein.

PCR detection of North American and Central African isolates of epizootic hemorrhagic disease virus (EHDV) based on genome segment 10 of EHDV serotype 1

PCR amplification technology for the detection of epizootic hemorrhagic disease virus (EHDV) ribonucleic acid in cell culture and clinical specimens was developed. With oligoribonucleotide primers selected from genome segment 10 of EHDV serotype 1 (EHDV-1), which codes for two nonstructural proteins (NS3 and NS3a), the PCR-based assay resulted in a 535-bp PCR product. RNAs from North American EHDV-1 prototype, EHDV-2 prototype, and a number of EHDV field isolates, including the Central African isolates of EHDV-5 and EHDV-318 propagated in cell cultures, were detected by this PCR-based assay. The specific 535-bp PCR products were visualized onto agarose gels, and the identity of the PCR products was confirmed by chemiluminescent hybridization with a 352-bp internal probe. The sensitivity of the EHDV PCR assay was increased by chemiluminescent hybridization; by this EHDV-NS3 PCR, 10 fg of EHDV RNA was detected (equivalent to 600 viral particles). Amplification product was not detected when the PCR-based assay was applied to RNAs from North American bluetongue virus prototype serotypes 2, 10, 11, 13, and 17; total nucleic acid extracts from uninfected BHK-21 cells; or unfractionated blood from calves and deer that were EHDV seronegative and virus isolation negative. The described EHDV PCR-based assay with primers derived from segment 10 of EHDV-1 resulted in detection of EHDV RNA from blood and tissues collected from calves and deer with natural and experimental EHDV infections and provides a valuable tool to study the epidemiology of EHDV infection in susceptible ruminants.

Epizootic hemorrhagic disease: analysis of tissues by amplification and in situ hybridization reveals widespread orbivirus infection at low copy numbers

A recent outbreak of hemorrhagic fever in wild ruminants in the northwest United States was characterized by rapid onset of fever, followed shortly thereafter by hemorrhage and death. As a result, a confirmed 1,000 white-tailed deer and pronghorn antelope died over the course of 3 months. Lesions were multisystemic and included severe edema, congestion, acute vascular necrosis, and hemorrhage. Animals that died with clinical signs and/or lesions consistent with hemorrhagic fever had antibody to epizootic hemorrhagic disease virus serotype 2 (EHDV-2) by radioimmune precipitation but the antibody was limited exclusively to class immunoglobulin M. These findings, indicative of acute infection, were corroborated by the observation that numerous deer were found dead; however, clinically affected deer were rarely seen during the outbreak. Furthermore, only in animals with hemorrhagic lesions was EHDV-2 isolated and/or erythrocyte-associated EHDV-2 RNA detected by serotype-specific reverse transcription (RT)-PCR. By using a novel RT in situ PCR assay, viral nucleic acid was localized to the cytoplasm of large numbers of tissue leukocytes and vascular endothelium in tissues with hemorrhage and to vessels, demonstrating acute intimal and medial necrosis. Because PCR amplification prior to in situ hybridization was essential for detecting EHDV, the virus copy number within individual cells was low, <20 virus copies. These findings suggest that massive covert infection characterized by rapid dissemination of virus facilitates the severe and lethal nature of this disease.

Bluetongue virus detection: a safer reverse-transcriptase polymerase chain reaction for prediction of viremia in sheep

A reversible target capture viral RNA extraction procedure was combined with a reverse-transcriptase nested polymerase chain reaction (PCR) to develop a capture PCR assay providing a rapid and safe prediction method for circulating bluetongue virus in infected ruminants. This new assay was compared with virus isolation and a recently developed antigen-capture enzyme-linked immunosorbent assay (ELISA) for the detection of bluetongue virus. Eight Warhill crossbred sheep were inoculated subcutaneously with bluetongue virus serotype 10, and blood samples were taken sequentially over a period of 28 days. The capture PCR detected the peak of viremia, as determined by virus isolation and antigen-capture ELISA, from day 5 to day 14 after challenge. The results indicate that the rapid-capture bluetongue virus PCR provides a rapid indicator of samples in which virus can be isolated. In addition, this capture bluetongue virus PCR procedure does not require a lengthy phenol extraction or the use of the highly toxic methyl mercury hydroxide denaturant.

Evaluation of nucleic acid amplification methods for the detection of hog cholera virus

A blind panel was tested in a diagnostic evaluation of a reverse transcription (RT) polymerase chain reaction (PCR) method for detecting hog cholera virus (HCV) from pig tissues. The capability of the RT-PCR test to discriminate between HCV and related pestiviruses, bovine viral diarrhea virus (BVDV), and those viruses causing similar diseases in swine, including African swine fever virus (ASFV) and pseudorabies virus (PRV), was also considered. Nucleic acid extraction involved either kit-based or conventional phenol:chloroform:isoamyl alcohol methods. A single-round PCR assay, using primers that hybridize to the conserved p120 nonstructural gene region, was 82.5% sensitive (n = 17) and 100% specific (n = 18) in the detection of the presence of HCV RNA. However, the sensitivity was increased to 100% following a second PCR test. In all, 4 HCV, 7 BVDV, 2 ASFV, and 1 PRV isolates were studied. Novel nucleic acid sequences were generated for 9 HCV strains. Analysis of a portion of the p120 region using these methods was suitable for HCV isolate characterization.

Geographical genetic variation in the gene encoding VP3 from the Alberta isolate of epizootic hemorrhagic disease virus

The complete nucleic acid and deduced amino acid sequences of gene segment 3 and the encoded VP3 from the North American, Alberta isolate of epizootic hemorrhagic disease virus serotype 2 (EHDV-2) are reported. Complementary DNA corresponding to segment 3 was 2768 nucleotides in length with an open reading frame of 2697 base pairs which encoded a VP3 polypeptide of 899 amino acid residues. Sequence comparison with genome segment 3 and VP3 from the Australian strain of EHDV-2 indicated genotypic and phenotypic homologies of 79% and 94%, respectively. Two North American field isolates of EHDV-2, as well as EHDV-1 (New Jersey isolate), had virtually identical homology to the Alberta isolate. Sequence analysis delineated North American EHDV strains as members of a genetically homologous and geographically distinct group of orbiviruses (topotype). The data support the hypothesis that geographic isolation between North American and Australian orbiviruses has permitted the viral topotypes to maintain their genetic distinctness.

A model for the membrane topology of the NS3 protein as predicted from the sequence of segment 10 of epizootic haemorrhagic disease virus serotype 1

Segment 10, encoding nonstructural proteins 3 (NS3) and 3a (NS3a) of epizootic haemorrhagic disease virus serotype 1 (EHDV-1) was sequenced. Computer motif recognition programs were used for interpretation of the sequence data to predict a structure for NS3. Integral membrane protein theories were then applied to produce a general topological model for the EHDV-1 NS3 protein. Homology was observed between EHDV-1 NS3 integral membrane motifs and those similarly observed in the cognate proteins of other orbiviruses.

Applications of DNA amplification techniques in veterinary diagnostics

An overview of the principles of the polymerase chain reaction, ligase chain reaction, self-sustained sequence replication and Q beta replicase is given. The application of these methods for the diagnosis of veterinary infectious and hereditary diseases as well as for other diagnostic purposes is discussed and comprehensive tables of reported assays are provided. Specific areas where these DNA-based amplification methods provide substantial advantages over traditional approaches are also highlighted. With regard to PCR-based assays for the detection of viral pathogens, this article is an update of a previous review by Belák and Ballagi-Pordány (1993).

Sequence analysis of the non-structural protein 2 from epizootic hemorrhagic disease viruses

The non-structural protein 2 (NS2) of epizootic hemorrhagic disease virus serotype 1 (EHD-1) was cloned and sequenced. The NS2 gene was found to be 1185 bp containing a single open reading frame that encodes a 376 amino acid protein. A 97% nucleic acid identity was found between EHD-1 and a previously published NS2 sequence of EHD-2. Only a 60% nucleic acid identity was found between EHD and the bluetongue virus (BTV) serogroup. Comparison of the deduced amino acid sequences revealed 97% identity within the EHD serogroup, and less than or equal to 43% identity between serogroups.