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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.
Antemortem detection of latent infection with neuropathogenic strains of equine herpesvirus-1 in horses. To evaluate a technique for identifying horses latently infected with neuropathogenic strains of equine herpesvirus-1 (EHV-1). Methods: 36 adult mares, 24 of which were experimentally infected as weanlings with neuropathogenic or nonneuropathogenic EHV-1. Methods: Mandibular lymph node (MLN) tissue was obtained from each horse via biopsy during general anesthesia. Purified DNA from MLNs was tested for EHV-1 DNA by use of a magnetic bead, sequencecapture, nested PCR assay. For MLNs that contained EHV-1 DNA, the 256-bp DNA fragments amplified via sequence-capture nested PCR were sequenced to det...
Equine herpesvirus 2-associated granulomatous dermatitis in a horse. Granulomatous dermatitis in horses has been linked to many etiologies, including various parasites, fungi, and bacteria. Idiopathic forms of granulomatous inflammation-producing diseases, some of which are localized to the skin, also have been reported in horses. Herein we describe a case of recurrent equine granulomatous skin disease characterized by intranuclear viral inclusions within macrophages and giant cells. The histologic changes were primarily noted in the deep dermis and included multifocal to coalescing areas of necrosis marked by histiocytic cell infiltration and presence of giant...
Application of polymerase chain reaction and virus isolation techniques for the detection of viruses in aborted and newborn foals. The occurrence of two important pathogens, equine herpesvirus 1 (EHV1) and equine arteritis virus (EAV) causing abortions, perinatal foal mortality and respiratory disease, was investigated by polymerase chain reaction (PCR) and virus isolation to demonstrate the presence of abortigenic viruses in samples from 248 horse fetuses in Hungary. We found 26 EHV1- and 4 EAV-positive aborted or prematurely born foals from 16 and 4 outbreaks, respectively, proving that despite the widely applied vaccination, EHV1 is a far more important cause of abortions in the studs than EAV. We compared the virus co...
Highly diverse type of equine arteritis virus (EAV) from the semen of a South African donkey: short communication. Equine arteritis virus (EAV) was detected by RT-nested PCR in semen samples from a naturally infected South African donkey. Sequence analysis of the amplified ORF5 fragment revealed only 60 to 70% nucleotide identity to a panel of EAV reference sequences. The unique donkey EAV sequence was also found to be stable during passage in horses. The sequence data reported in this study indicate that the South African donkey variant might represent a new genotype of EAV. The distinct genetic properties of the South African asinine strain of EAV suggest a divergent evolution of this arterivirus in vari...
Inability of kaolin treatment to remove nonspecific inhibitors from equine serum for the hemagglutination inhibition test against equine H7N7 influenza virus. The hemagglutination inhibition test is used by many diagnostic and surveillance laboratories for detection of antibodies to influenza viruses. It is well known that the hemagglutination inhibition test is affected by nonspecific inhibitors present in equine serum. Several serum treatments are in use to remove these inhibitors, including treatment with kaolin. Discrepant results were observed in the authors' laboratories when using kaolin treatment before testing equine sera for antibodies against equine influenza virus (EIV) subtype-1 (H7N7). It is demonstrated here that kaolin treatment lead...
EIAV vector-mediated delivery of endostatin or angiostatin inhibits angiogenesis and vascular hyperpermeability in experimental CNV. We evaluated the efficacy of equine infectious anaemia virus (EIAV)-based lentiviral vectors encoding endostatin (EIAV.endostatin) or angiostatin (EIAV.angiostatin) in inhibiting angiogenesis and vascular hyperpermeability in the laser-induced model of choroidal neovascularisation (CNV). Equine infectious anaemia virus.endostatin, EIAV.angiostatin or control (EIAV.null) vectors were administered into the subretinal space of C57Bl/6J mice. Two weeks after laser injury CNV areas and the degree of vascular hyperpermeability were measured by image analysis of in vivo fluorescein angiograms. Compar...
Temporal detection of equine herpesvirus infections of a cohort of mares and their foals. The objectives of this study were to estimate the prevalence of equine herpesviruses (EHV) 1-5 in the nasal secretions (NS) of a cohort of 12 mares and their foals from birth to 6 months of age, estimate the prevalence of EHV-1-5 infection of peripheral blood mononuclear cells (PBMC) of selected foals, and investigate phylogenetic relationships amongst the various strains of EHV-2 and 5. Virus-specific PCR assays were used to detect EHV-1-5 in NS and PBMC. A homologous portion of the glycoprotein B (gB) gene of the various strains of EHV-2 and 5 was sequenced and compared. EHV-2, 4, and 5 were...
[Tick-borne encephalitis (TBE) with special emphasis on infection in horses]. The tick-borne encephalitis (TBE), also known as early summer meningo-encephalitis, is a geographically limited virus infection transmitted mainly by ticks. The importance of TBE is largely underestimated. The causative agent TBE-Virus (TBEV) is grouped into the genus Flavivirus of the virus family Flaviviridae. Clinical disease including fatal outcomes has been described for men and dogs. With regard to horses only a limited number of case reports is available. In a study performed at the Institute of Virology, Justus-Liebig-University Giessen serum samples from the German endemic region of M...
Effective removal of equine arteritis virus from stallion semen. A method of removing equine arteritis virus (EAV) from equine semen used for artificial insemination is urgently needed. Recent medical studies suggest that a double semen processing technique of density gradient centrifugation followed by a 'swim-up' can provide virus-free sperm preparations for assisted reproduction. Objective: To investigate the use of the double semen processing technique to obtain virus-free sperm preparations from stallion semen containing EAV. Methods: Aliquots of an ejaculate from an uninfected stallion were spiked with virus and processed by the double processing tech...
Quantification by real-time PCR of the magnitude and duration of leucocyte-associated viraemia in horses infected with neuropathogenic vs. non-neuropathogenic strains of EHV-1. Neurological disease in horses caused by infection with certain 'paralytic' strains of equine herpesvirus-1 (EHV-1) is a potentially devastating condition the pathogenesis of which is poorly understood. Preliminary observations in both experimentally induced and naturally occurring cases of the central nervous system disease have revealed a more robust cell-associated viraemia in horses infected with paralytic isolates of EHV-1, relative to horses infected with abortigenic isolates. To investigate further this pathogenesis-relevant question, the present study was performed using a greater numb...
RT-PCR for detection of all seven genotypes of Lyssavirus genus. The Lyssavirus genus includes seven species or genotypes named 1-7. Rabies genotypes correlate with geographical distribution and specific hosts. Co-circulation of different lyssaviruses, imported cases, and the presence of unknown viruses, such as Aravan, Khujand, Irkut and West Caucasian Bat Virus, make it necessary to use generic methods able to detect all lyssaviruses. Primer sequences were chosen from conserved regions in all genotypes in order to optimise a generic RT-PCR. Serial dilutions of 12 RNA extracts from all seven Lyssavirus genotypes were examined to compare the sensitivity of ...
Five-year surveillance of West Nile and eastern equine encephalitis viruses in Southeastern Virginia. To investigate the occurrence of West Nile virus (WNV) and Eastern equine encephalitis virus (EEE) in southeastern Virginia, the Bureau of Laboratories at the Norfolk Department of Public Health (NDPH) analyzed mosquito pools and the sera of sentinel chickens from the southeastern Virginia area each year from 2000 to 2004. Mosquito pool supernatants were screened for the presence of viral RNA by conventional reverse transcription polymerase chain reaction (RT-PCR) and Taqman RT-PCR with the i-Cycler. Mosquito pools were also tested for virus activity by Vero cell culture. The primary enzootic ...
Antibodies to West Nile virus in asymptomatic mammals, birds, and reptiles in the Yucatan Peninsula of Mexico. Surveillance for evidence of West Nile virus (WNV) infection in taxonomically diverse vertebrates was conducted in the Yucatan Peninsula of Mexico in 2003 and 2004. Sera from 144 horses on Cozumel Island, Quintana Roo State, 415 vertebrates (257 birds, 52 mammals, and 106 reptiles) belonging to 61 species from the Merida Zoo, Yucatan State, and 7 farmed crocodiles in Ciudad del Carmen, Campeche State were assayed for antibodies to flaviviruses. Ninety (62%) horses on Cozumel Island had epitope-blocking enzyme-linked immunosorbent assay (ELISA) antibodies to flaviviruses, of which 75 (52%) were...
In vitro efficacies of oseltamivir carboxylate and zanamivir against equine influenza A viruses. To investigate the possibilities of two NA inhibitors [oseltamivir carboxylate (OC) and zanamivir (ZA)] as the clinical agents for equine influenza A virus (EIV) infection, we examined the efficacies of these inhibitors against twelve EIVs in vitro. OC and ZA inhibited NA activities of all EIVs with 50% inhibitory concentrations with ranging from 0.017 to 0.130 and from 0.010 to 0.074 microM, respectively. OC and ZA inhibited plaque-forming of all EIVs in MDCK cells with 50% effective concentrations with ranging from 0.015 to 0.097 and from 0.016 to 0.089 microM, respectively, except for one s...
Extended phylogeny of equine arteritis virus: division into new subgroups. To determine a conclusive phylogeny, equine arteritis viruses from Italy, Austria, Hungary, Sweden, South Africa and other parts of the world were analysed by reverse-transcription polymerase chain reaction amplification and direct sequencing. The nucleotide sequences corresponding to the variable part of the large glycoprotein GP5, specified by open reading frame 5, were compared and added to a previously published phylogenetic tree in which a clear division between 'European' and 'American' type viruses had been established. Adding the sequences determined in this study and new sequences ret...
Antibody and IFN-gamma responses induced by a recombinant canarypox vaccine and challenge infection with equine influenza virus. In horses, equine influenza virus (EIV) is a leading cause of respiratory disease. Conventional inactivated vaccines induce a short-lived immune response. By comparison, natural infection confers a long-term immunity to re-infection. An aim of new equine influenza vaccines is to more closely mimic natural infection in order to achieve a better quality of immunity. A new live recombinant vaccine derived from the canarypox virus vector and expressing haemagglutinin genes of EIV (subtype H3N8) has been developed. Stimulation of the immune system was studied after immunisation with this canarypox-...
Isolation and genetic analysis of Japanese encephalitis virus from a diseased horse in Japan. Japanese encephalitis (JE) developed in an unvaccinated half-bred horse kept in Tottori Prefecture, Japan. The animal showed ataxia with pyrexia and low appetite, and ultimately died. A viral strain was isolated from the cerebrum of the horse and was identified as JE virus (JEV) by RT-PCR using JEV specific primers. The isolated JEV was classified into genotype I by nucleotide sequence analysis of the viral envelope gene. We believe that this is the first report of the genotype I strain being isolated from a horse.
Use of DNA and recombinant canarypox viral (ALVAC) vectors for equine herpes virus vaccination. In this study, experimental canarypox virus (ALVAC) and plasmid DNA recombinant vaccines expressing the gB, gC and gD glycoproteins of EHV-1 were assessed for their ability to protect conventional ponies against a respiratory challenge with EHV-1. In addition, potential means of enhancing serological responses in horses to ALVAC and DNA vaccination were explored. These included co-administration of the antigen with conventional adjuvants, complexation with DMRIE-DOPE and co-expression of the antigen along with equine GM-CSF. Groups of EHV primed ponies were vaccinated twice intra-muscularly wi...
Analysis of equid herpesvirus 1 strain variation reveals a point mutation of the DNA polymerase strongly associated with neuropathogenic versus nonneuropathogenic disease outbreaks. Equid herpesvirus 1 (EHV-1) can cause a wide spectrum of diseases ranging from inapparent respiratory infection to the induction of abortion and, in extreme cases, neurological disease resulting in paralysis and ultimately death. It has been suggested that distinct strains of EHV-1 that differ in pathogenic capacity circulate in the field. In order to investigate this hypothesis, it was necessary to identify genetic markers that allow subgroups of related strains to be identified. We have determined all of the genetic differences between a neuropathogenic strain (Ab4) and a nonneuropathogenic ...
Antibody and cellular immune responses following DNA vaccination and EHV-1 infection of ponies. Equine herpesvirus-1 (EHV-1) is the cause of serious disease with high economic impact on the horse industry, as outbreaks of EHV-1 disease occur every year despite the frequent use of vaccines. Cytotoxic T-lymphocytes (CTLs) are important for protection from primary and reactivating latent EHV-1 infection. DNA vaccination is a powerful technique for stimulating CTLs, and the aim of this study was to assess antibody and cellular immune responses and protection resulting from DNA vaccination of ponies with combinations of EHV-1 genes. Fifteen ponies were divided into three groups of five ponies...
Inoculation of mares and very young foals with EHV-1 glycoproteins D and B reduces virus shedding following respiratory challenge with EHV-1. We have previously demonstrated that intramuscular inoculation of EHV-1 glycoprotein D (gD) and glycoprotein B (gB) produced by a recombinant baculovirus and formulated with the adjuvant Iscomatrix elicited virus-neutralizing antibody and gD- and gB-specific ELISA antibody in adult horses. In this study, 14 mares and their very young foals were inoculated with a combination of baculovirus-expressed EHV-1 gD and EHV-1 gB (EHV-1 gDBr) and challenged with a respiratory strain of EHV-1. Following experimental challenge, inoculated mares and foals shed virus in nasal secretions on significantly few...
The S2 accessory gene of equine infectious anemia virus is essential for expression of disease in ponies. Equine infectious anemia virus (EIAV) is a macrophage-tropic lentivirus that persistently infects horses and causes a disease that is characterized by periodic episodes of fever, thrombocytopenia, and viremia. EIAV encodes only four regulatory/accessory genes, (tat, rev, ttm, and S2) and is the least genetically complex of all known lentiviruses. We sought to determine the role of the EIAV S2 accessory gene of EIAV by introducing mutations that would prevent S2 expression on the p19/wenv17 infectious molecular clone. Virus derived from the p19/wenv17 molecular clone is highly virulent and rout...
Mucosal and systemic adjuvant activity of alphavirus replicon particles. Vaccination represents the most effective control measure in the fight against infectious diseases. Local mucosal immune responses are critical for protection from, and resolution of, infection by numerous mucosal pathogens. Antigen processing across mucosal surfaces is the natural route by which mucosal immunity is generated, as peripheral antigen delivery typically fails to induce mucosal immune responses. However, we demonstrate in this article that mucosal immune responses are evident at multiple mucosal surfaces after parenteral delivery of Venezuelan equine encephalitis virus replicon pa...
Combined amino acid mutations occurring in the envelope closely correlate with pathogenicity of EIAV. The Chinese equine infectious anemia virus (EIAV) donkey-leukocyte attenuated vaccine (DLV) provides a unique natural model system to study the attenuation mechanism and immunological control of lentivirus replication. Critical consensus mutations were identified between virulent Chinese EIAV strains and vaccine strains. Based on a full-length infectious clone of EIAV vaccine strain pLGFD3, two molecular clones, mFD5-4-7 and mFD7-2-11, were successfully constructed, in which 4 and 6 critical consensus mutations in the env gene of the vaccine strain were point-mutated to the wild-type sequence,...
Postepizootic persistence of Venezuelan equine encephalitis virus, Venezuela. Five years after the apparent end of the major 1995 Venezuelan equine encephalitis (VEE) epizootic/epidemic, focal outbreaks of equine encephalitis occurred in Carabobo and Barinas States of western Venezuela. Virus isolates from horses in each location were nearly identical in sequence to 1995 isolates, which suggests natural persistence of subtype IC VEE virus (VEEV) strains in a genetically stable mode. Serologic evidence indicated that additional outbreaks occurred in Barinas State in 2003. Field studies identified known Culex (Melanoconion) spp. vectors and reservoir hosts of enzootic VEE...
Equine herpesvirus 1 glycoprotein D expressed in E. coli provides partial protection against equine herpesvirus infection in mice and elicits virus-neutralizing antibodies in the horse. The envelope glycoprotein D of EHV-1 (EHV-1 gD) is essential for virus infectivity and entry of virus into cells and is a potent inducer of virus-neutralizing antibody. In this study, truncated EHV-1 gD (gDt) was expressed with a C-terminal hexahistidine tag in E. coli using a pET vector. Western blot analysis using an anti-gD monoclonal antibody demonstrated the presence of gDt bands at 37.5, 36, 29.5 and 28 kDa. The immunogenicity and protective efficacy of partially purified gDt was compared with gD expressed in insect cells by a recombinant baculovirus (Bac gD) using a BALB/c mouse model o...
Immune escape of equine herpesvirus 1 and other herpesviruses of veterinary importance. Equine herpesvirus (EHV)-1 is a pathogen of horses, well known for its ability to induce abortion and nervous system disorders. Clinical signs may occur despite the presence of a virus-specific immune response in the horse. The current review will summarize the research, on how, EHV-1-infected cells can hide from recognition by the immune system. Research findings on immune evasion of EHV-1 will be compared with those of other herpesviruses of veterinary importance.
[West Nile virus infection: serological investigation among horses in France and in Africa]. This study was carried out in 2003 to detected serological evidence of West Nile virus infection in 190 Army horses kept nearby French troops stationed in Southeast France and in Africa (Chad, Côte d'Ivoire and Senegal). Both IgG and IgM antibodies were searched for using an ELISA assay. Specifiity of IgG antibodies was determined by western blot and plaque reduction seroneutraization. Finding showed that 79% of the Army horses (n=96) tested in Africa presented specific IgG antibodies. All horses that were seropositive for IgG were seronegative for IgM. None of the Army horses (n=94) tested i...
Equine herpesvirus type 1 modified live virus vaccines: quo vaditis? Infections of horses with equine herpesvirus type 1 (EHV-1) have garnered new attention over the last few years. Devastating outbreaks occurring worldwide, primarily of the neurologic form of the disease, have resulted in a reassessment of the control strategies, and particularly the prophylactic measures, that are necessary to keep the infection and spread of disease in check. Most of the available EHV-1 vaccines are based on preparations of inactivated virus, which are applied monovalently for prevention of EHV-1-caused abortion in pregnant mares or as part of multivalent vaccines to prevent...
