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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.
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...
Equine herpesvirus 4 DNA in trigeminal ganglia of naturally infected horses detected by direct in situ PCR. Neuronal and lymphoid tissues of 15 randomly selected horses were analysed post mortem by liquid nested-PCR to study the tropism of equine herpesvirus 4 (EHV-4). In four animals the trigeminal ganglia and in one case the lung were positive. Using a direct in situ PCR the EHV-4 genome was localized in the nuclei of neurons and in the bronchiolar as well as alveolar epithelium of the lung. In none of these tissues could infectious virus or viral antigens be detected. Applying the more sensitive liquid RT-PCR, however, an acute infection was demonstrated in one of the trigeminal ganglia by amplif...
Detection and distribution of equine herpesvirus 2 DNA in the central and peripheral nervous systems of ponies. The distribution of equine herpesvirus 2 (EHV-2) DNA within neurological and lymphoid tissues from 12 EHV-2 seropositive Welsh mountain ponies was determined by PCR. The lymphoid sites sampled in this study were almost universally PCR positive, thus confirming the existing virus co-cultivation data which suggest that the lymph nodes draining the respiratory tract are the main reservoirs of EHV-2 DNA. In addition, EHV-2 DNA was also detected, albeit with lower frequency, within both the peripheral and central nervous systems (PNS and CNS) of these animals. Of the CNS sites sampled 11% were PCR-...
Herpesviral abortion in domestic animals. Abortion or neonatal disease may follow infection with several alpha, beta and gamma-herpesviruses. The alpha-herpesvirus, equid herpesvirus-1 (EHV-1), causes single or epizootic abortions or neonatal deaths in equids, and the closely related virus EHV-4 causes sporadic equine abortions. In cattle, the alpha-herpesviruses, bovine herpesvirus-1 (infectious bovine rhinotracheitis virus) and bovine herpesvirus-5 (bovine encephalitis virus), and a gamma-herpesvirus, bovine herpesvirus-4, have all been implicated as causes of abortion. In pigs, suid herpesvirus-1 (SHV-1: pseudorabies virus), an alp...
Melatonin protects mice infected with Venezuelan equine encephalomyelitis virus. We investigated whether the administration of melatonin (MLT) reduces the death rate and evolution of the disease in mice infected with Venezuelan equine encephalomyelitis (VEE) virus. Our results show that, MLT protects mice infected with the virus. The mortality rate was reduced from 100% to 16% merely by increasing the dose from 0 to 1000 micrograms/MLT per kg body weight MLT significantly postponed the onset of the disease and death by several days. In surviving mice very high titres of VEE virus IgM antibodies were found seven weeks after virus inoculation. MLT significantly reduced VEE v...
Cloning, expression, purification, and characterization of the major core protein (p26) from equine infectious anemia virus. The gene coding for the major core protein (p26) of the lentivirus equine infectious anemia virus (EIAV) was cloned from EIAV infected serum, expressed in E. coli, and the resultant protein purified to electrophoretic homogeneity. The protein was expressed in a soluble form and was purified by conventional protein separation methods. When analyzed by SDS-PAGE, under both reducing and non-reducing conditions, the purified protein migrated as a 26 kDa monomer. Recombinant p26 (rp26), therefore, does not contain any intermolecular disulfide bond. Gel filtration chromatography also indicated that ...
An outbreak of respiratory disease in horses associated with Mycoplasma felis infection. Lower respiratory tract disease developed in a group of racehorses in training between two and six years of age. Disease was observed in 22 of 25 horses for which full records were available. Seroconversion to Mycoplasma felis was demonstrated by indirect haemagglutination assay in 19 of 22 paired sera and high titres (> or = 64) were found in convalescent sera from the three remaining horses. Evidence of respiratory viral infection was confined to seroconversions to equine herpesvirus-4 in two of the horses. Tracheal wash samples, taken from four horses with visibly increased tracheal muco...
A novel family of viral death effector domain-containing molecules that inhibit both CD-95- and tumor necrosis factor receptor-1-induced apoptosis. Molluscum contagiosum virus proteins MC159 and MC160 and the equine herpesvirus 2 protein E8 share substantial homology to the death effector domain present in the adaptor molecule Fas-associated death domain protein (FADD) and the initiating death protease FADD-like interleukin-1beta-converting enzyme (FLICE) (caspase-8). FADD and FLICE participate in generating the death signal from both tumor necrosis factor receptor-1 (TNFR-1) and the CD-95 receptor. The flow of death signals from TNFR-1 occurs through the adaptor molecule tumor necrosis factor receptor-associated death domain protein (TRA...
Insertions, duplications and substitutions in restricted gp90 regions of equine infectious anaemia virus during febrile episodes in an experimentally infected horse. We have studied a horse which exhibited typical clinical signs of disease when experimentally infected with a non-adapted virulent strain of equine infectious anaemia virus (EIAV), designated V70. Five viruses (F1V, F2V, F3V, F4V and F5V) were recovered during periodic febrile episodes. Cross-neutralization tests revealed that all of these variants and the parental V70 were antigenically distinct. Sequencing of their full-length env gp90 genes and gp45 5' sequences revealed novel mutations at a limited number of nucleotide positions, consisting of insertions and duplications in the gp90 princi...
Study of the duration and distribution of equine influenza virus subtype 2 (H3N8) antigens in experimentally infected ponies in vivo. The purpose of this experiment was to study the duration and distribution of equine influenza virus in actively infected ponies over a 3 wk period. Pony foals (6-8 mo old) were infected experimentally by nebulizing equine influenza subtype-2 virus ultrasonically through a face mask. Successful infection was clinically apparent as each of the foals (n = 6) had a febrile response, a deep hacking cough and mucopurulent nasal discharge for 7 to 10 d. The virus was isolated from nasopharyngeal swabs of all the ponies 3 and 5 d after infection and all the ponies seroconverted to the virus. Samples w...
Restriction endonuclease analysis of equine herpesvirus-1 isolates recovered in Ontario, 1986-1992, from aborted, stillborn, and neonatal foals. Ninety-two equine herpesvirus type 1 isolates were recovered from aborted, stillborn, or neonatal foals from Ontario, Canada, from 1986 to 1992. From this total, 32 strains were randomly chosen for further study. Four or 5 isolates from each winter were selected, each from a different premises, and characterized by restriction enzyme analysis using BamHI, KpnI, BglII, HindIII, and EcoRI. Additional isolates from 2 premises and from a zebra foal were also assessed. For the strains isolated in 1986 and 1989-1992, the DNA pattern of 18 strains was similar to that of type 1P (Kentucky D) for BamHI...
An infectious arterivirus cDNA clone: identification of a replicase point mutation that abolishes discontinuous mRNA transcription. Equine arteritis virus (EAV) is a positive-strand RNA virus that uses a discontinuous transcription mechanism to generate a nested set of six subgenomic mRNAs from which its structural genes are expressed. A stable bacterial plasmid (pEAV030) containing a full-length cDNA copy of the 12.7-kb EAV genome was constructed. After removal of a single point mutation in the replicase gene, RNA transcripts generated in vitro from pEAV030 were shown to be infectious upon electroporation into BHK-21 cells. A genetic marker mutation was introduced at the cDNA level and recovered from the genome of the pro...
Serologic markers in early stages of African horse sickness virus infection. Fifteen horses were experimentally infected with African horse sickness virus (AHSV) serotype 4. To learn more about the time course of production and specificity of AHSV-specific antibodies, sera were analyzed by immunoblot analysis. Only animals that survived for more than 9 days were able to develop a humoral immune response detectable by immunoblotting. The earliest serological markers corresponded mainly to VP5, VP6, and NS2 and to a lesser extent to VP3, NS1, and NS3. Neutralizing antibodies to VP2 were not detected by immunoblotting, suggesting that they are mostly conformation dependen...
Gazelle herpesvirus 1: a new neurotropic herpesvirus immunologically related to equine herpesvirus 1. A herpesvirus was isolated from Thomson's gazelle (Gazella thomsoni) kept at a zoological garden in Japan during an outbreak of epizootic acute encephalitis. The virus, gazelle herpesvirus 1 (GHV-1), was serologically related to equine herpesvirus 1 (EHV-1). However, DNA fingerprints of GHV-1 were different from those of EHV-1 and other equine herpesviruses. Southern hybridization with probes of cloned BamHI fragments derived from UL and US segments of EHV-1 revealed differences in the DNA restriction profiles throughout the entire genome. Nucleotide sequences were determined for a conserved r...
[Re-emergence of Venezuelan equine encephalitis virus in French Guiana. Apropos of 1 confirmed case]. Venezuelan equine encephalitis (VEE) is a mosquito-borne viral disease that occurs in equine species and in man. The strains can be grouped epidemiologically into two major categories: enzootic and epizootic. Enzootic strains cause sporadic human disease and are not associated with disease among equines. These strains are found throughout Florida. Central America, northern South America and Brazil. Epizootic strains are associated with enormous morbidity and mortality in equine species. In man, VEE virus infections are largely asymptomatic and in children and young adults there is an increased...
Infectious agents in acute respiratory disease in horses in Ontario. A study of acute respiratory disease in horses in Ontario was undertaken to determine the identity of current causative infectious agents. A nasopharyngeal swab was designed and utilized to maximize isolation of viruses, mycoplasma, and pathogenic bacteria. Serum samples were collected for parallel determination of antibody titers to equine influenza virus type A subtype 1 (H7N7) and subtype 2 (H3N8), equine rhinovirus types 1 and 2, equine herpesvirus type 1, Mycoplasma equirhinius, and Mycoplasma felis. Equine rhinovirus type 2 was recovered from 28/92 horses tested, and equine influenza vir...
Application of equine infectious anemia virus core proteins produced in a baculovirus expression system to serological diagnosis. Equine infectious anemia virus (EIAV) core proteins were obtained from a baculovirus expression system. Recombinant baculoviruses (rBVs) highly expressed the Gag precursor and p26 antigens in an rBV-infected Sf21 cell culture supernatant. Enzyme-linked immunosorbent assay (ELISA) and agar gel immunodiffusion (AGID) were conducted using the expressed proteins to detect antibodies from experimentally infected horses. The expressed antigens showed low background levels, high specificity and sensitivity in ELISA and AGID. The results of the serological tests using the expressed antigens were ident...
A survey for antibodies to equine arteritis virus in donkeys, mules and zebra using virus neutralisation (VN) and enzyme linked immunosorbent assay (ELISA). A seroepidemiological survey of donkeys in South Africa (n = 4300) indicated a wide distribution and increasing prevalence of antibodies to equine arteritis virus (EAV). Donkey sera inhibited equine arteritis virus infection in virus neutralisation (VN) tests and in ELISA specifically bound to a recombinant antigen derived from the Bucyrus isolate of EAV. These results suggest that donkeys have been exposed to the same serotype of this virus as circulates among horses. A good correlation existed between EAV neutralising antibody titres and ELISA absorbance values (0.8631); the ELISA was sensit...
Identification, cloning and sequence analysis of the equine adenovirus 1 hexon gene. Based on sequence homology with human adenovirus 2 (HAdV2), the hexon gene of equine adenovirus 1 (EAdV1) was identified. HindIII restriction fragments containing the hexon and other viral genes were cloned into the plasmids pUC19 and pBlueScript SK(-) and sequenced. The nucleotide sequence of the hexon gene was completely determined and partial sequence data were obtained for seven other EAdV1 genes. Amino acid (aa) sequence comparison with published adenovirus (AdV) proteins identified the genes for the IIIa, penton, pVII, PVI, 23K proteinase, DNA binding and 100K proteins. The eight EAdV1 g...
Mutational changes in the hemagglutinin of equine H3 influenza viruses result in the introduction of a glycosylation site which enhances the infectivity of the viruses. The complete amino acid sequences of the hemagglutinin (HA) glycoprotein of three equine-2 influenza viruses from tropical Africa are presented in comparison with that of a well characterized European equine-2 virus (Suffolk/89) and a consensus sequence from the database. The sequences of the tropical African viruses were deduced from the complete nucleotide sequences of their HA genes reported earlier. Mutational changes in the nucleotide sequences resulted in amino acid changes in the HA which led to the introduction of a new asparagine-linked (N-linked) glycosylation site in two viruses. Th...
Expression of equine morbillivirus (EMV) matrix and fusion proteins and their evaluation as diagnostic reagents. Full-length cDNA clones coding for the matrix (M) and fusion (F) proteins of equine morbillivirus (EMV) were isolated by RT-PCR, and expressed in Escherichia coli using two different expression systems. Western blot analysis indicated that the M and F proteins, expressed either by itself or as fusion proteins with glutathione S-transferase (GST), were insoluble and degraded after expression. Analysis of the degradation pattern of recombinant M protein suggested that the N-terminus of the matrix protein might be more stable and antigenic than the C-terminal region. Therefore a third system was ...
Direct detection of equine herpesvirus DNA in tissues of aborted equine fetuses. Restriction endonuclease analysis of equine herpesviruses 1 (EHV-1) and 4 has been investigated using cultured cells infected with these viruses. The DNA cleavage patterns of these viruses were observed in the intracellular DNA after digestion with Eco RI and electrophoresis. This procedure was applied to the diagnosis of equine herpesvirus infection in aborted equine fetuses. The characteristic Eco RI restriction pattern of EHV-1 DNA was directly detectable in the emulsion of lungs collected from aborted equine fetuses.
[Immunopathology of Borna disease in the horse: clinical, virological and neuropathologic findings]. Tissues from nine horses and one donkey suffering from natural Borna disease were investigated. Clinically, all animals demonstrated progressive reduced mentation and aggravating gait disturbances. During the clinical course anorexia and progressive loss of proprioception were observed. Cranial nerve failure was accompanied by signs of pharyngeal paralysis, sialorrhea, bruxism, and by blindness. Virologically, infectious virus was detected in the brain of all animals investigated but was not found regularly in all areas of the brain. However, in all cases, infectivity was found in the thalamus...
Analysis of the long terminal repeat from a cytopathic strain of equine infectious anemia virus. Sequential passage of the tissue culture-adapted prototype strain of EIAV in fetal donkey dermal (FDD) cell cultures generated a virus stock which exhibits cytopathic effects in FDD cell cultures. In this study, the effects of the long terminal repeat (LTR) region on virus replication and cytopathogenicity were examined. The FDD-adapted virus LTR was found to contain a number of base pair mutations and a large insertion within the U3 region in comparison with the previously characterized LTR, lambda12. Transient gene expression studies showed that basal promoter activity, in FDD cell cultures,...
