Comparative susceptibility of eastern cottontails and New Zealand white rabbits to classical rabbit haemorrhagic disease virus (RHDV) and RHDV2.

Rabbit haemorrhagic disease virus (RHDV) is associated with high morbidity and mortality in the European rabbit (Oryctolagus cuniculus). In 2010, a genetically distinct RHDV named RHDV2 emerged in Europe and spread to many other regions, including North America in 2016. Prior to this study it was unknown if eastern cottontails (ECT(s); Sylvilagus floridanus), one of the most common wild lagomorphs in the United States, were susceptible to RHDV2. In this study, 10 wild-caught ECTs and 10 New Zealand white rabbits (NZWR(s); O. cuniculus) were each inoculated orally with either RHDV (RHDVa/GI.1a; n = 5 per species) or RHDV2 (a recombinant GI.1bP-GI.2; n = 5 per species) and monitored for the development of disease. Three of the five ECTs that were infected with RHDV2 developed disease consistent with RHD and died at 4 and 6 days post-inoculation (DPI). The RHDV major capsid protein/antigen (VP60) was detected in the livers of three ECTs infected with RHDV2, but none was detected in the ECTs infected with RHDV. Additionally, RHD viral RNA was detected in the liver, spleen, intestine and blood of ECTs infected with RHDV2, but not in the ECTs infected with RHDV. RHD viral RNA was detected in urine, oral swabs and rectal swabs in at least two of five ECTs infected with RHDV2. One ECT inoculated with RHDV2 seroconverted and developed a high antibody titre by the end of the experimental period (21 DPI). ECTs inoculated with the classic RHDV did not seroconvert. In comparison, NZWRs inoculated with RHDV2 exhibited high mortality (five of five) at 2 DPI and four of five NZWRs inoculated with RHDV either died or were euthanized at 2 DPI indicating both of these viruses were highly pathogenic to this species. This experiment indicates that ECTs are susceptible to RHDV2 and can shed viral RNA, thereby suggesting this species could be involved in the epidemiology of this virus.

Increased Virulence of an Epidemic Strain of Vesicular Stomatitis Virus Is Associated With Interference of the Innate Response in Pigs.

Vesicular stomatitis virus (VSV) causes sporadic outbreaks of vesicular disease in the southwestern United States. The intrinsic characteristics of epidemic strains associated with these outbreaks are poorly understood. In this study, we report the distinctive genomic and biological characteristics of an epidemic (NJ0612NME6) strain of VSV compared with an endemic (NJ0806VCB) strain. Genomic comparisons between the two strains revealed a total of 111 nucleotide differences (23 non-synonymous) with potentially relevant replacements located in the P, G, and L proteins. When tested in experimentally infected pigs, a natural host of VSV, the epidemic strain caused higher fever and an increased number of vesicular lesions compared to pigs infected with the endemic strain. Pigs infected with the epidemic strain showed decreased systemic antiviral activity (type I - IFN), lower antibody levels, higher levels of interleukin 6, and lower levels of tumor necrosis factor during the acute phase of disease compared to pigs infected with the endemic strain. Furthermore, we document the existence of an RNAemia phase in pigs experimentally infected with VSV and explored the cause for the lack of recovery of infectious virus from blood. Finally, the epidemic strain was shown to be more efficient in down-regulating transcription of IRF-7 in primary porcine macrophages. Collectively, the data shows that the epidemic strain of VSV we tested has an enhanced ability to modulate the innate immune response of the vertebrate host. Further studies are needed to examine other epidemic strains and what contributions a phenotype of increased virulence might have on the transmission of VSV during epizootics.

Real-Time Reverse Transcription PCR Assay for Detection of Senecavirus A in Swine Vesicular Diagnostic Specimens.

Senecavirus A (SV-A), formerly, Seneca Valley virus (SVV), has been detected in swine with vesicular lesions and is thought to be associated with swine idiopathic vesicular disease (SIVD), a vesicular disease syndrome that lacks a defined causative agent. The clinical presentation of SIVD resembles that of other more contagious and economically devastating vesicular diseases, such as foot-and-mouth disease (FMD), swine vesicular disease (SVD), and vesicular stomatitis (VS), that typically require immediate rule out diagnostics to lift restrictions on animal quarantine, movement, and trade. This study presents the development of a sensitive, SYBR Green RT-qPCR assay suitable for detection of SV-A in diagnostic swine specimens. After testing 50 pigs with clinical signs consistent with vesicular disease, 44 (88%) were found to be positive for SV-A by RT-qPCR as compared to none from a negative cohort of 35 animals without vesicular disease, indicating that the assay is able to successfully detect the virus in an endemic population. SV-A RNA was also detectable at a low level in sera from a subset of pigs that presented with (18%) or without (6%) vesicular signs. In 2015, there has been an increase in the occurrence of SV-A in the US, and over 200 specimens submitted to our laboratory for vesicular investigation have tested positive for the virus using this method. SV-A RNA was detectable in all common types of vesicular specimens including swabs and tissue from hoof lesions, oral and snout epithelium, oral swabs, scabs, and internal organ tissues such as liver and lymph node. Genome sequencing analysis from recent virus isolates was performed to confirm target amplicon specificity and was aligned to previous isolates.

Isolation and characterization of a Cervidpoxvirus from a goitered gazelle (Gazella subgutturosa) from a zoologic park in Minnesota.

Deerpox virus (DPV) is the sole member of the newly ratified Cervidpoxvirus genus in the subfamily Chordopoxvirinae. Presented here is the first diagnostic report of isolation of DPV from a goitered gazelle (Gazella subgutturosa). A tissue homogenate was submitted by a zoologic park to the Minnesota Veterinary Diagnostic Laboratory at the University of Minnesota for poxvirus diagnostic investigation and then referred to Plum Island Foreign Animal Disease Diagnostic Laboratory for confirmation. Poxviral infection was confirmed using electron microscopy. The virus was cultured in vero cells and subjected to further diagnoses for characterization. Polymerase chain reaction targeting the major envelope (B2L) protein and RNA polymerase of parapoxviruses, and the poly-A polymerase gene of capripoxviruses, were all negative. Degenerative pan-poxvirus primers that target the DNA polymerase (DNApol) and DNA topoisomerase (DNAtopo) genes, however, successfully amplified poxviral DNA fragments. Amplification of the DNApol and DNAtopo genes yielded fragments of 543 and 344 base pairs, respectively. DNA sequence and phylogenetic analysis of each gene fragment from the gazelle isolate showed >97% identity in BLAST searches with two DPV virus strains (W848-83 and W-1170-84) isolated from North American mule deer (Odocoileus hemionus) in 1983-1984. Neighbor-joining trees indicate that the isolate is a member of the Cervidpoxvirus genus and shows a more-distant relationship to other ruminant poxviruses, namely the Capripoxvirus genus consisting of lumpy skin disease, sheeppox, and goatpox viruses. This report documents the premiere finding of DPV, a recently characterized virus, in gazelles and demonstrates the need for broadened investigation when diagnosing poxvirus infections in ruminants.

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.

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.