Health knowledge and infection control by event horse owners

Infection control and quarantine measures are essential to minimise the impact of equine infectious diseases, but their uptake by equestrians involved with sport horses in the United Kingdom is undocumented. Using a questionnaire, this study aimed to: i) determine the knowledge and practices of eventing equestrians about their horses’ health and the clinical signs of endemic and exotic equine infectious diseases and ii) assess existing infection control and quarantine measures on event horse yards. A questionnaire was designed, piloted and distributed electronically over six weeks. The target respondents were equestrians involved in eventing, including jumping their horses over fences either 100cms. Data were described qualitatively and analysed statistically to identify any relationships between selected parameters. A total of 146 responses were analysed. The majority of respondents were female, involved as amateurs in eventing and their veterinary surgeon was the first choice for advice. To assess temperature,owners often used touch, but rectal temperature was taken rarely. The majority of horses were vaccinated against tetanus and influenza but a minority against EHV-1/-4. Most respondents identified the clinical signs of influenza and Streptococcus equi, but were less certain about EHV-1/-4. Only 30.1% of respondents had access to quarantine facilities, which were significantly more likely to be available in professional yards (p=0.043) and in riders competing above the 100cm level (p=0.0003). Professionals competing their horses above 100cm were significantly more likely to have quarantine facilities (p<0.05). A majority of yards with quarantine facilities isolated new horses for 2-4 weeks. Facilities included a separate stable (81.8%) or field (68.2%), but separate equipment (47.7%) and access to disinfectant (36.4%) were available less frequently. In conclusion, amateur equestrians involved in eventing require better education on the routine use of infection control and quarantine measures to minimise the impact of equine infectious diseases and thus strengthen infection control nationally

Health knowledge and infection control by event horse owners

Infection control and quarantine measures are essential to minimise the impact of equine infectious diseases, but their uptake by equestrians involved with sport horses in the United Kingdom is undocumented. Using a questionnaire, this study aimed to: i) determine the knowledge and practices of eventing equestrians about their horses’ health and the clinical signs of endemic and exotic equine infectious diseases and ii) assess existing infection control and quarantine measures on event horse yards. A questionnaire was designed, piloted and distributed electronically over six weeks. The target respondents were equestrians involved in eventing, including jumping their horses over fences either 100cms. Data were described qualitatively and analysed statistically to identify any relationships between selected parameters. A total of 146 responses were analysed. The majority of respondents were female, involved as amateurs in eventing and their veterinary surgeon was the first choice for advice. To assess temperature,owners often used touch, but rectal temperature was taken rarely. The majority of horses were vaccinated against tetanus and influenza but a minority against EHV-1/-4. Most respondents identified the clinical signs of influenza and Streptococcus equi, but were less certain about EHV-1/-4. Only 30.1% of respondents had access to quarantine facilities, which were significantly more likely to be available in professional yards (p=0.043) and in riders competing above the 100cm level (p=0.0003). Professionals competing their horses above 100cm were significantly more likely to have quarantine facilities (p<0.05). A majority of yards with quarantine facilities isolated new horses for 2-4 weeks. Facilities included a separate stable (81.8%) or field (68.2%), but separate equipment (47.7%) and access to disinfectant (36.4%) were available less frequently. In conclusion, amateur equestrians involved in eventing require better education on the routine use of infection control and quarantine measures to minimise the impact of equine infectious diseases and thus strengthen infection control nationally

Health knowledge and infection control by event horse owners

Infection control and quarantine measures are essential to minimise the impact of equine infectious diseases, but their uptake by equestrians involved with sport horses in the United Kingdom is undocumented. Using a questionnaire, this study aimed to: i) determine the knowledge and practices of eventing equestrians about their horses’ health and the clinical signs of endemic and exotic equine infectious diseases and ii) assess existing infection control and quarantine measures on event horse yards. A questionnaire was designed, piloted and distributed electronically over six weeks. The target respondents were equestrians involved in eventing, including jumping their horses over fences either 100cms. Data were described qualitatively and analysed statistically to identify any relationships between selected parameters. A total of 146 responses were analysed. The majority of respondents were female, involved as amateurs in eventing and their veterinary surgeon was the first choice for advice. To assess temperature,owners often used touch, but rectal temperature was taken rarely. The majority of horses were vaccinated against tetanus and influenza but a minority against EHV-1/-4. Most respondents identified the clinical signs of influenza and Streptococcus equi, but were less certain about EHV-1/-4. Only 30.1% of respondents had access to quarantine facilities, which were significantly more likely to be available in professional yards (p=0.043) and in riders competing above the 100cm level (p=0.0003). Professionals competing their horses above 100cm were significantly more likely to have quarantine facilities (

Vaccination of foals with a modified live, equid herpesvirus-1 gM deletion mutant (RacHΔgM) confers partial protection against infection

Equid herpesvirus-1 (EHV-1) causes respiratory and neurological disease and late gestation abortion in pregnant mares. Current vaccines contain either inactivated or live EHV-1, but fail to provide complete clinical or virological protection, namely prevention of nasopharyngeal shedding and cell-associated viraemia. Thus, the development of novel products, such as modified live virus (MLV) vaccines which stimulate virus-specific, humoral and cell mediated immune responses more effectively remains a priority. Two groups of weaned foals (n = 6 each group) were used in a longitudinal, prospective, experimental study to evaluate immune responses elicited by two vaccinations with a glycoprotein M (gM) deletion mutant of EHV-1 (RacHdeltagM). Following two concurrent intranasal and intramuscular inoculations six weeks apart, vaccinated (8.4 ± 0.2 months old) and control foals (6.2 ± 0.4 months) were challenge infected intranasally with EHV-1 Ab4/8 four weeks after the second vaccination and clinical signs and virological replication measured. Vaccination caused no adverse events, but did stimulate significantly higher complement fixing and virus neutralizing antibodies in serum compared with control foals at either equivalent or pre-vaccination time points. Virus-specific nasopharyngeal antibody levels and cytotoxic T lymphocyte responses were not significantly different between the groups. Following challenge infection, these immune responses were associated with a reduction in clinical signs and virological replication in the vaccinated foals, including a reduction in duration and magnitude of pyrexia, nasopharyngeal shedding and cell-associated viraemia. We conclude that the RacHΔgM MLV primed EHV-1-specific humoral immune responses in weaned foals. However, complete virological protection by vaccination against EHV-1 requires further research

Polarisation of equine pregnancy outcome is associated with a maternal MHC class I allele

Identification of risk factors which are associated with severe clinical signs can assist in the management of disease outbreaks and indicate future research areas. Pregnancy loss during late gestation in the mare compromises welfare, reduces fecundity and has financial implications for horse owners. This retrospective study focussed on the identification of risk factors associated with pregnancy loss among 46 Thoroughbred mares on a single British stud farm, with some but not all losses involving equid herpesvirus-1 (EHV-1) infection. In a sub-group of 30 mares, association between pregnancy loss and the presence of five common Thoroughbred horse haplotypes of the equine Major Histocompatibility Complex (MHC) was assessed. This involved development of sequence specific, reverse transcriptase polymerase chain reactions and in several mares, EHV-1 specific, cytotoxic T lymphocyte activity. Of the 46 mares, 10 suffered late gestation pregnancy loss or neonatal foal death, five of which were EHV-1 positive. Maternal factors including age, parity, number of EHV-1 specific vaccinations and the number of days between final vaccination and foaling or abortion were not significantly associated with pregnancy loss. In contrast, a statistically significant association between the presence of the MHC class I B2 allele and pregnancy loss was identified, regardless of the fetus / foal’s EHV-1 status (p=0.002). In conclusion, this study demonstrated a significantly positive association between pregnancy loss in Thoroughbred mares and a specific MHC class I allele in the mother. This association requires independent validation and further investigation of the mechanism by which the mare’s genetic background contributes to pregnancy outcome

Immediate early protein of equid herpesvirus type 1 as a target for cytotoxic T-lymphocytes in the thoroughbred horse

Cytotoxic T-lymphocytes (CTLs) are associated with protective immunity against disease caused by equid herpesvirus type 1 (EHV-1). However, the EHV-1 target proteins for CTLs are poorly defined. This limits the development of vaccine candidates designed to stimulate strong CTL immunity. Here, classical CTL assays using lymphocytes from horses of three defined MHC class I types that experienced natural infection with EHV-1 and a modified vaccinia virus construct containing an EHV-1 gene encoding the immediate-early (IE) protein are reported. Horses homozygous for the equine leukocyte antigen (ELA)-A2 haplotype, but not the ELA-A5 haplotype, produced MHC-restricted CTL responses against the IE protein. Previously, horses homozygous for the ELA-A3 haplotype also mounted CTL responses against the IE protein. Both haplotypes are common in major horse breeds, including the Thoroughbred. Thus, the IE protein is an attractive candidate molecule for future studies of T-cell immunity to EHV-1 in the horse

A Point Mutation in a Herpesvirus Polymerase Determines Neuropathogenicity

Infection with equid herpesvirus type 1 (EHV-1) leads to respiratory disease, abortion, and neurologic disorders in horses. Molecular epidemiology studies have demonstrated that a single nucleotide polymorphism resulting in an amino acid variation of the EHV-1 DNA polymerase (N752/D752) is significantly associated with the neuropathogenic potential of naturally occurring strains. To test the hypothesis that this single amino acid exchange by itself influences neuropathogenicity, we generated recombinant viruses with differing polymerase sequences. Here we show that the N752 mutant virus caused no neurologic signs in the natural host, while the D752 virus was able to cause inflammation of the central nervous system and ataxia. Neurologic disease induced by the D752 virus was concomitant with significantly increased levels of viremia (p = 0.01), but the magnitude of virus shedding from the nasal mucosa was similar between the N752 and D752 viruses. Both viruses replicated with similar kinetics in fibroblasts and epithelial cells, but exhibited differences in leukocyte tropism. Last, we observed a significant increase (p < 0.001) in sensitivity of the N752 mutant to aphidicolin, a drug targeting the viral polymerase. Our results demonstrate that a single amino acid variation in a herpesvirus enzyme can influence neuropathogenic potential without having a major effect on virus shedding from infected animals, which is important for horizontal spread in a population. This observation is very interesting from an evolutionary standpoint and is consistent with data indicating that the N752 DNA pol genotype is predominant in the EHV-1 population, suggesting that decreased viral pathogenicity in the natural host might not be at the expense of less efficient inter-individual transmission

Frequency and phenotype of EHV-1 specific, IFN-γ synthesising lymphocytes in ponies: The effects of age, pregnancy and infection

Equine herpesvirus-1 (EHV-1) infects horses, causing acute respiratory disease, neurological signs, and is also a leading cause of abortion. Protection from EHV-1 infection and disease depends on both humoral (virus neutralising antibody) and cellular (mainly cytotoxic T lymphocytes, CTL) immune responses. CTL activity after EHV-1 infection has been extensively investigated and is closely associated with an alternative measure of cell mediated immunity (CMI), interferon-gamma (IFN-γ) synthesis. This study investigates EHV-1-specific IFN-γ synthesising cells in potentially immunocompromised horses; foals, pregnant mares and aged animals, after field or experimental infection with EHV-1. In foals and pregnant mares, the kinetics after experimental infection were similar and the phenotype of IFN-γ+ synthesising cells after EHV-1 stimulation was mainly CD8α+. In contrast, in samples collected from primed healthy ponies exposed to EHV-1 several months previously or in old ponies (28 years old), the majority of EHV-1-specific IFN-γ+ lymphocytes expressed a CD5+, CD8α− phenotype. This study highlights the complexity of the relationship between EHV-1, a common pathogen in horses, and the virus-specific cellular immune response as measured using IFN-γ synthesis

Polarisation of equine pregnancy outcome is associated with a maternal MHC class I allele

Identification of risk factors which are associated with severe clinical signs can assist in the management of disease outbreaks and indicate future research areas. Pregnancy loss during late gestation in the mare compromises welfare, reduces fecundity and has financial implications for horse owners. This retrospective study focussed on the identification of risk factors associated with pregnancy loss among 46 Thoroughbred mares on a single British stud farm, with some but not all losses involving equid herpesvirus-1 (EHV-1) infection. In a sub-group of 30 mares, association between pregnancy loss and the presence of five common Thoroughbred horse haplotypes of the equine Major Histocompatibility Complex (MHC) was assessed. This involved development of sequence specific, reverse transcriptase polymerase chain reactions and in several mares, EHV-1 specific, cytotoxic T lymphocyte activity. Of the 46 mares, 10 suffered late gestation pregnancy loss or neonatal foal death, five of which were EHV-1 positive. Maternal factors including age, parity, number of EHV-1 specific vaccinations and the number of days between final vaccination and foaling or abortion were not significantly associated with pregnancy loss. In contrast, a statistically significant association between the presence of the MHC class I B2 allele and pregnancy loss was identified, regardless of the fetus / foal’s EHV-1 status (p=0.002). In conclusion, this study demonstrated a significantly positive association between pregnancy loss in Thoroughbred mares and a specific MHC class I allele in the mother. This association requires independent validation and further investigation of the mechanism by which the mare’s genetic background contributes to pregnancy outcome