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Topic:Virology
Virology in horses encompasses the study of viruses that affect equine species, including their biology, transmission, and impact on horse health. This field investigates viral pathogens that can lead to a range of diseases, from respiratory infections to neurological disorders. Common viruses affecting horses include equine influenza virus, equine herpesvirus, and West Nile virus. Understanding these viruses involves examining their genetic makeup, modes of transmission, and interactions with the equine immune system. This page compiles peer-reviewed research studies and scholarly articles that explore the epidemiology, pathogenesis, and control measures of viral infections in horses.
A novel P/V/C gene in a new member of the Paramyxoviridae family, which causes lethal infection in humans, horses, and other animals. In 1994, a new member of the family Paramyxoviridae isolated from fatal cases of respiratory disease in horses and humans was shown to be distantly related to morbilliviruses and provisionally called equine morbillivirus (K. Murray et al., Science 268:94-97, 1995). To facilitate characterization and classification, the virus was purified, viral proteins were identified, and the P/V/C gene was cloned and sequenced. The coding strategy of the gene is similar to that of Sendai and measles viruses, members of the Paramyxovirus and Morbillivirus genera, respectively, in the subfamily Paramyxovirina...
Development and characterization of an in vivo pathogenic molecular clone of equine infectious anemia virus. An infectious nonpathogenic molecular clone (19-2-6A) of equine infectious anemia virus (EIAV) was modified by substitution of a 3.3-kbp fragment amplified by PCR techniques from a pathogenic variant (EIAV(PV)) of the cell culture-adapted strain of EIAV (EIAV(PR)). This substitution consisted of coding sequences for 77 amino acids at the carboxyl terminus of the integrase, the S1 (encoding the second exon of tat), S2, and S3 (encoding the second exon of rev) open reading frames, the complete env gene (including the first exon of rev), and the 3' long terminal repeat (LTR). Modified 19-2-6A mol...
Pathogenesis and clinical signs of equine herpesvirus-1 in experimentally infected ponies in vivo. Equine herpesvirus-1 (EHV-1) causes respiratory disease, neonatal death, abortion and neurologic disease. The main purpose of this study was to identify viral antigen in respiratory tract samples by immunoperoxidase staining. Six pony foals were selected on the basis of demonstrating seronegativity to EHV-1 by virus neutralization and housed in isolation. They were infected experimentally by administering EHV-1 nebulized ultrasonically through a face mask. Successful infection was clinically apparent as each of the foals had febrile responses, nasal discharge, and enlarged submandibular lymph ...
Comparison of nucleic and amino acid sequences and phylogenetic analysis of open reading frames 3 and 4 of various equine arteritis virus isolates. The genetic variation in equine arteritis virus (EAV) protein-encoding open reading frames (ORFs) 3 and 4 genes was investigated. Nucleic and deduced amino acid sequences from seven different EAV isolates (one European, one American and five Canadian isolates) and the Arvac vaccine strain were compared with those of Bucyrus reference strain. ORF 3 nucleotide and amino acid sequence identities between these isolates (including the Arvac vaccine strain) and the Bucyrus reference strain ranged from 85.6 to 98.8%, and 85.3 to 98.2%, respectively, whereas ORF 4 nucleotide and amino acid sequence id...
Expression cloning and humoral immune response to the nucleocapsid and membrane proteins of equine arteritis virus. To provide a convenient and sensitive method for the detection of equine arteritis virus (EAV)-specific serum antibodies, we developed an immunoblot assay employing the EAV nucleocapsid (N) and membrane (M) proteins expressed in a procaryotic expression vector (pMAL-c2) for the production of recombinant maltose-binding (MBP) fusion proteins (MBP-N and MBP-M). The antigenic reactivity of the recombinant fusion proteins and their Xa factor cleavage EAV products was confirmed by immunoblot using horse antisera to EAV. Some horse sera, however, showed immune reactivity to the MBP fusion partner pr...
Characterisation of gamma herpesviruses in the horse by PCR. A polymerase chain reaction (PCR) based on a combination of oligonucleotide primers selected using the octamer frequency disparity method with primers specific for EHV-5 (described by other authors) recognized all of a series of gamma herpesvirus field isolates. This PCR produced only three fragments: (1) one EHV-2-specific; (2) one EHV-5-specific; and (3) a fragment that occurred alone or in combination with the other two. Cloning and sequencing of four different isolates yielding only the last PCR product showed that this corresponds to a deletion/insertion mutant of EHV-2. The fact that thi...
Infection of bone marrow macrophages by equine infectious anemia virus. To characterize infection of bone marrow-derived macrophages (BMDM) with equine infectious anemia virus (EIAV) by determining virus production, effects on viability, and induction of cytokines. Methods: BMDM obtained from bone marrow of 6 clinically normal adult horses. Methods: BMDM were infected with EIAV at a multiplicity of infection of 8. Cell viability, percentage of cells with detectable viral protein, reverse transcriptase activity, and concentrations of infective virus (focus-forming units/ml), interleukin 6, and tumor necrosis factor-alpha were measured in culture supernatant samples...
Antibodies against equine herpesviruses in free-ranging mountain zebras from Namibia. Twenty-one blood samples of free-ranging mountain zebras (Equus zebra) from Namibia were tested for equine herpesvirus (EHV-1, -2, -3, -4) specific antibodies by immunofluorescence assay (IFA) and neutralization test (NT). Additionally, type-specific nested polymerase chain reactions (nested PCR) were employed for detection of EHV-1, -2 and -4 DNA. Equine herpesvirus-1 antibodies were detected by IFA in all zebras, while only seven serum samples contained EHV-4 IFA antibodies. Sera with high IFA antibodies also were found to neutralize EHV-1 and -4. Furthermore, 20 zebras were EHV-2 seropositi...
Novel and dynamic evolution of equine infectious anemia virus genomic quasispecies associated with sequential disease cycles in an experimentally infected pony. We have investigated the genetic evolution of three functionally distinct regions of the equine infectious anemia virus (EIAV) genome (env, rev, and long terminal repeat) during recurring febrile episodes in a pony experimentally infected with a well-characterized reference biological clone designated EIAV(PV). Viral populations present in the plasma of an EIAV(PV)-infected pony during sequential febrile episodes (18, 34, 80, 106, and 337 days postinfection) were amplified from viral RNA, analyzed, and compared to the inoculated strain. The comparison of the viral quasispecies showed that the ...
Hemagglutination with equine arteritis virus. Equine arteritis virus (EAV) grown on RK13 cell cultures was tested for hemagglutination (HA) with erythrocytes from a variety of species at 4 degrees C, room temperature and 37 degrees C. HA was observed at all temperatures with erythrocytes from mouse and chicken but not with those of cattle, horse, rabbit, guinea pig, mongolian gerbil, goose or chick embryo. Chickens showed an individual variation in agglutinability of their erythrocytes, requiring selection of birds to obtain erythrocytes for HA. The HA activity was enhanced by treatment of virus materials with Tween 80 followed by treatme...
The pathogenesis of ED71, a defined deletion mutant of equine herpesvirus-1, in a murine intranasal infection model for equine abortion. A series of mutants of equine herpesvirus-1 (EHV-1) which contain deletions in non-essential genes was previously characterized in a murine intranasal infection model. One mutant, ED71 which was shown to be attenuated in the model, was further characterized by inoculation into pregnant mice. Despite the attenuation previously reported, intranasal inoculation of pregnant mice resulted in premature parturition and the birth of dead or dying foetuses. Furthermore, mice inoculated before pregnancy with the same mutant, and subsequently challenged 14 days after conception with wild-type virus, were...
Repeated emergence of epidemic/epizootic Venezuelan equine encephalitis from a single genotype of enzootic subtype ID virus. Venezuelan equine encephalitis (VEE) epidemics and equine epizootics occurred periodically in the Americas from the 1920s until the early 1970s, when the causative viruses, subtypes IAB and IC, were postulated to have become extinct. Recent outbreaks in Columbia and Venezuela have renewed interest in the source of epidemic/epizootic viruses and their mechanism of interepizootic maintenance. We performed phylogenetic analyses of VEE virus isolates spanning the entire temporal and geographic range of strains available, using 857-nucleotide reverse transcription-PCR products including the E3 and ...
Equine infectious anemia virus utilizes a YXXL motif within the late assembly domain of the Gag p9 protein. We have previously demonstrated that the Gag p9 protein of equine infectious anemia virus (EIAV) is functionally homologous with Rous sarcoma virus (RSV) p2b and human immunodeficiency virus type 1 (HIV-1) p6 in providing a critical late assembly function in RSV Gag-mediated budding from transfected COS-1 cells (L. J. Parent et al., J. Virol. 69:5455-5460, 1995). In light of the absence of amino acid sequence homology between EIAV p9 and the functional homologs of RSV and HIV-1, we have now designed an EIAV Gag-mediated budding assay to define the late assembly (L) domain peptide sequences con...
Detection of equine arteritis virus in the semen of carrier stallions by using a sensitive nested PCR assay. A nested PCR, developed for the detection of equine arteritis virus (EAV) in semen, detected less than 2.5 PFU of EAV per ml of naturally infected seminal plasma. Based on results from testing 88 semen samples from 70 stallions, the sensitivity and specificity of the test were 100 and 97%, respectively.
In vivo dynamics of equine infectious anemia viruses emerging during febrile episodes: insertions/duplications at the principal neutralizing domain. Equine infectious anemia virus (EIAV) is a good model for studying mechanisms generating escaped retrovirus variants. We previously sequenced the entire gp90-encoding region of 22 cDNA clones obtained from five antigenically distinct isolates (F1V to F5V) recovered during febrile episodes in horse 493 experimentally infected with the Japanese virulent EIAV strain V70. The results showed that the mutations occurred in the principal neutralizing domain (PND) by insertions/duplications. In this study, we further characterized the PND of virus isolates sequentially recovered during 22 febrile epis...
Sequence analysis of equine adenovirus 2 hexon and 23K proteinase genes indicates a phylogenetic origin distinct from equine adenovirus 1. We report the first nucleotide sequence data on equine adenovirus 2 (EAdV2) which corroborate on the molecular level that EAdV2 is distinct from equine adenovirus 1 (EAdV1). Based on sequence homology with Eadv1 the hexon gene of Eadv2 was identified. HindIII restriction fragments containing the hexon and eight other viral genes were cloned into the plasmid pUC19 and the nucleotide sequence of the hexon and the 23K proteinase genes completely determined. Amino acid (aa) comparison of sequence fragments with published adenovirus (AdV) proteins identified the genes for the E1B/19K, IVa2, DNA pol...
The ICP0 protein of equine herpesvirus 1 is an early protein that independently transactivates expression of all classes of viral promoters. To assess the role of the equine herpesvirus type 1 (EHV-1) ICP0 protein (EICP0) in gene regulation, a variety of molecular studies on the EICP0 gene and gene products of both the attenuated cell culture-adapted Kentucky A (KyA) strain and the Ab4p strain were conducted. These investigations revealed that (i) the ICP0 open reading frame (ORF) of the KyA virus strain is 1,257 bp in size and would encode a protein of 419 amino acids, and in comparison to the ICP0 gene (ORF63) of the Ab4p strain of 1,596 bp (E. A. Telford, M. S. Watson, K. McBride, and A. J. Davison, Virology 189:304-316, 1992), ...
Borna disease virus infection in animals and humans. The geographic distribution and host range of Borna disease (BD), a fatal neurologic disease of horses and sheep, are larger than previously thought. The etiologic agent, Borna disease virus (BDV), has been identified as an enveloped nonsegmented negative-strand RNA virus with unique properties of replication. Data indicate a high degree of genetic stability of BDV in its natural host, the horse. Studies in the Lewis rat have shown that BDV replication does not directly influence vital functions; rather, the disease is caused by a virus-induced T-cell mediated immune reaction. Because antibodi...
Demonstration of Borna disease virus (BDV) in specific regions of the brain from horses positive for serum antibodies to BDV but negative for BDV RNA in the blood and internal organs. Sero- and molecular-epidemiological studies on Borna disease virus (BDV) infection show that BDV RNA is not always detected in the peripheral blood mononuclear cells (PBMCs) from serum anti-BDV antibody-positive individuals such as horses, sheep, cattle, cats, and humans. In this study we demonstrated BDV RNA signals by polymerase chain reaction only in restricted regions of the brain from horses with locomotor disease. Four of six horses examined showed apparently positive reactions for anti-BDV antibodies. Specific regions of the brain of these four horses were positive for BDV RNA but the i...
Experimental exposure of pregnant mares to the asinine-94 strain of equine arteritis virus. Clinical, virological and serological responses were evaluated in 10 pregnant mares after different challenge exposures to the asinine-94 strain of equine arteritis virus (EAV). The outcome of maternal infection on the progeny was also investigated. Mares were inoculated intranasally (n = 4), intramuscularly (n = 2), intravenously (n = 1), or contract-exposed (n = 3). All inoculated mares developed pyrexia, 5 showed mild clinical signs related to EAV infection and 2 remained asymptomatic. Viraemia was detected in all the inoculated animals and shedding of virus from the respiratory tract occur...
Effect of the South African asinine-94 strain of equine arteritis virus (EAV) in pregnant donkey mares and duration of maternal immunity in foals. Clinical, virological and serological responses were investigated in five pregnant donkey mares after experimental exposure to the South African asinine-94 strain of equine arteritis virus (EAV), and the duration of maternal immunity to EAV was studied in their foals. In four intranasally inoculated mares, fever with maximum rectal temperatures of 39.1-40.7 degrees C was recorded 2-11 d after challenge. All the inoculated mares developed mild depression, and a serous ocular and nasal discharge; in three mares mild conjuctivitis was observed. The virus was recovered from the nasopharynx and fro...
Antibodies against some viruses of domestic animals in southern African wild animals. Twenty-four species of South African wild animals were tested for the presence of antibodies against the viruses of 16 common diseases of domestic animals. Positive results were obtained for African horsesickness, equine encephalosis, equid herpes virus-1, infectious bovine rhinotracheitis, Allerton disease (Herpes mammillitis), lumpy skin disease, parainfluenza, encephalomyocarditis, bluetongue, Wesselsbron disease, bovine ephemeral fever, and Akabane disease complex. No antibodies could be demonstrated against the viruses of equine influenza, equine infectious anaemia, equine viral arteritis...
An outbreak of abortion in mares associated with Salmonella abortusequi infection. An abortion outbreak occurred in a herd of 38 horses, 26 of which were pregnant mares. Twenty-one mares aborted between 5-10 months of gestation. In no case were there indications of impending abortion. Pathoanatomical, histopathological, virological and bacteriological examinations were carried out on 4 aborted fetuses. Histopathology identified Gram-negative bacteria compatible with salmonella in all 4 placentae. By subsequent bacteriological examination Salmonella abortusequi was isolated as the single causative agent in each case. Nonmotile Salmonella abortusequi with antigenic formula 4,1...
Detection of latency-associated transcripts of equid herpesvirus 1 in equine leukocytes but not in trigeminal ganglia. Results from Southern hybridization and PCR amplification experiments using a randomly synthesized reverse transcription-PCR product showed that peripheral blood leukocytes from horses showing no clinical signs of disease expressed a putative latency-associated transcript antisense to and overlapping the 3' end of the equid herpesvirus 1 (EHV-1) immediate-early gene (gene 64). A PCR product derived from this transcript has > or =96% identity with the published EHV-1 sequence. In situ hybridization studies of equine bronchial lymph nodes corroborated these findings and are consistent with re...
Maturation of the cellular and humoral immune responses to persistent infection in horses by equine infectious anemia virus is a complex and lengthy process. Equine infectious anemia virus (EIAV) provides a natural model system by which immunological control of lentivirus infections may be studied. To date, no detailed study addressing in parallel both the humoral and cellular immune responses induced in horses upon infection by EIAV has been conducted. Therefore, we initiated the first comprehensive characterization of the cellular and humoral immune responses during clinical progression from chronic disease to inapparent stages of EIAV infection. Using new analyses of antibody avidity and antibody epitope conformation dependence that had not been...
Equine viral arteritis in newborn foals: clinical, pathological, serological, microbiological and immunohistochemical observations. Clinical, pathological, immunohistochemical, serological and microbiological findings are described for 2 geographically and temporally distinct equine arteritis virus (EAV) epidemics in newborn foals. Outbreak A occurred at a commercial Standardbred breeding facility; Outbreak B began in a group of research animals. Clinical signs were severe and primarily referable to the respiratory tract. Fever and leucopenia and/or thrombocytopenia were observed in foals surviving for more than 24 h. The most common gross pathological findings were limited to the respiratory tract. Common histopathologica...
Detection of African horse sickness virus in the blood of experimentally infected horses: comparison of virus isolation and a PCR assay. A reverse transcription-polymerase chain reaction (RT-PCR) assay followed by dot-blot hybridisation was used to detect African horse sickness virus (AHSV); the primers employed amplified the S7 gene that encodes the VP7 protein. The RT-PCR assay was compared with virus isolation for detecting AHSV in blood samples form horses experimentally infected with AHSV-4 and AHSV-9. The influence of sample storage and transportation and the effects of two anticoagulants (EDTA and heparin) were also studied. RT-PCR results were obtained within 48 hours as opposed to a minimum of 15 days for virus isolati...
Cardio-histopathological observations on aborted equine fetuses infected with equid herpesvirus 1 (EHV-1). Twenty-five aborted equine fetuses infected with equid herpesvirus 1 (EHV-1) were examined cardio-histopathologically. The main changes in the heart consisted of interstitial myocarditis and intramyocardial vascular lesions accompanied by degeneration and necrosis of the cardiac myocytes. Vascular pathology of intramyocardial small arteries and arterioles was characterized by endothelial cell necrosis and fibrinoid changes in the media. Eosinophilic intranuclear inclusion bodies characteristic of herpesvirus infection were detected in the myocardial cells and macrophages within and around the ...
Expression of the nonstructural protein NS1 of equine influenza A virus: detection of anti-NS1 antibody in post infection equine sera. The nucleotide sequence of the nonstructural protein NS1 of the influenza virus A/equine 2/Suffolk/89 was determined and found to be 97% identical to that of A/equine 2/Miami/63. A similar level of identity was shown for the deduced NS1 amino acid sequence. The NS1 gene was expressed, in its entirety and in part, as fusion proteins with glutathione S-transferase using the pGEX-3X expression vector. Antibodies to NS1 protein were detected in serum samples from ponies experimentally infected with influenza virus, but not in animals vaccinated with whole inactivated virus or in unprimed control a...
