Prevalence of equine herpesvirus types 2 and 5 in horse populations by using type-specific PCR assays

Equineherpesvirustypes 2 and 5 (EHV-2andEHV-5)have a rather unclearpathogenicity and distribution within the equid population. In order to gain more information on the prevalence of these two viruses, type-specific PCR assays were developed to detect viral DNA in nasal specimens and in peripheral blood leukocytes (PBLs) of adult horses and foals from various regions of Europe, i.e. Sweden, Hungary and the United Kingdom. In adult horses, the prevalence of EHV-2 in PBLs was up to 68% in Sweden and 71% in the United Kingdom. EHV-2 DNA was detected in the PBLs from all the foals tested in all countries and most (93%) of the nasal specimens also yielded positive results. The prevalence of EHV-5 DNA in the PBLs of foals in Hungary was 15 and 24% in adult horses in the United Kingdom. This observation was among the very few reports of the presence of EHV-5 in horses. In summary, the specific PCR assays revealed important data on the occurrence and distribution of EHV-2 and EHV-5 in large horse populations. The findings indicated that infection with EHV-5 occurred later than EHV-2 in foals. This study may contribute to a better understanding of the etiological role of these gammaherpesviruses in equine diseases.     

Prevalence of equine herpesvirus-1 and equine herpesvirus-4 infections in equidae species in Turkey as determined by ELISA and multiplex nested PCR

In this report we examined the presence of specific antibodies against equine herpesvirus type 1 (EHV-1), and equine herpesvirus type 4 (EHV-4) in several equidae, including mules, donkeys, horses. The presence of EHV-1 and EHV-4 in respiratory diseases of equids, and ability of multiplex nested polymerase chain reaction (PCR) screening in simultaneous diagnosis of horses acutely infected by EHV-1 and EHV-4 were also investigated. Sera from 504 horses, mules and donkeys sampled were tested for the presence of EHV-1 and EHV-4 specific antibodies. Blood samples taken from 21 symptomatic horses and nasal swabs taken from 40 symptomatic horses were tested for the presence of EHV-1 and EHV-4 by a multiplex nested PCR. A total of 14.3% (3/21) of buffy coat samples and 32.5% (13/40) nasal swab samples were found to contain EHV-1 DNA, while 19% (4/21) buffy coat samples and 22.5% (9/40) nasal swab samples were found to be positive for EHV-4 DNA. By species, 14.5% of horses, 37.2% of mules and 24.2% of donkeys tested were EHV-1 seropositive. EHV-4 specific antibodies were detected in 237 (81.7%) of 290 horse sera tested. Results from this investigation demonstrate that EHV-1 and EHV-4 are prevalent throughout the equid population, and that donkeys and mules might also represent an important source of infection for other equids. We also showed that the multiplex nested PCR assay might be useful for diagnosis of mixed respiratory infections in horses due to EHV-1 and EHV-4.     

EHV-1 gene63 is not essential for in vivo replication in horses and mice, nor does it affect reactivation in the horse: short communication

The aim of this study was to investigate the role of immediate early gene (gene63) in the pathogenesis of equine herpesvirus 1 (EHV-1) acute and latent infections in equine and murine models. EHV-1 gene63 mutant virus (g63mut) along with EHV-1 (Ab4) was used for intracerebral and intranasal infection of 3 and 17-day-old mice. Both viruses were recovered at the same frequency from tissues after infection. Two Welsh ponies were infected via the intranasal route with each of the viruses. Acute infection was monitored by virus isolation from nasal swabs and peripheral blood leukocytes. Six weeks post infection, peripheral blood leukocytes were taken from ponies and in vitro reactivation was positive for both viruses. At autopsy, both viruses were isolated by co-cultivation from bronchial and submandibular lymph nodes. These findings indicate that the mutation of EHV-1 gene63 does not play a role in the establishment and reactivation from latency.     

Study of equid herpesviruses 2 and 5 in Iceland with a type-specific polymerase chain reaction

The horse population in Iceland is a special breed, isolated from other horses for at least 1000 years. This provides an exceptional opportunity to investigate old and new pathogens in an inbred herd with few infectious diseases. We have developed a high sensitivity semi-nested PCR to study equid gammaherpesviruses 2 and 5 (EHV-2 and 5) in Iceland. The first PCR is group specific, the second type-specific, targeting a 113bp sequence in the glyB gene. DNA isolated from white blood cells and 18 different organs was tested for the presence of EHV-2 and 5. This was done in adult horses and foals, healthy and with various enteric infections. Both virus types were easily detected in all types of organs tested or EHV-2 in 79% cases and EHV-5 in 63%. In DNA from PBMC or buffy-coat EHV-2 was found in 20% cases and EHV-5 in 10%, all except one positive were foals. Co-culture of PBMC on fetal horse kidney cells was efficient for detecting EHV-2 but not for EHV-5. We verify here for the first time infections with EHV-2 and 5 in horses in Iceland and show that both viruses are common.     

Study of equid herpesviruses 2 and 5 in Iceland with a type-specific polymerase chain reaction

The horse population in Iceland is a special breed, isolated from other horses for at least 1000 years. This provides an exceptional opportunity to investigate old and new pathogens in an inbred herd with few infectious diseases. We have developed a high sensitivity semi-nested PCR to study equid gammaherpesviruses 2 and 5 (EHV-2 and 5) in Iceland. The first PCR is group specific, the second type-specific, targeting a 113 bp sequence in the glyB gene. DNA isolated from white blood cells and 18 different organs was tested for the presence of EHV-2 and 5. This was done in adult horses and foals, healthy and with various enteric infections. Both virus types were easily detected in all types of organs tested or EHV-2 in 79% cases and EHV-5 in 63%. In DNA from PBMC or buffy-coat EHV-2 was found in 20% cases and EHV-5 in 10%, all except one positive were foals. Co-culture of PBMC on fetal horse kidney cells was efficient for detecting EHV-2 but not for EHV-5. We verify here for the first time infections with EHV-2 and 5 in horses in Iceland and show that both viruses are common.     

Multiplex real-time PCR for the detection and differentiation of equid herpesvirus 1 (EHV-1) and equid herpesvirus 4 (EHV-4)

A multiplex real-time PCR was designed to detect and differentiate equid herpesvirus 1 (EHV-1) and equid herpesvirus 4 (EHV-4). The PCR targets the glycoprotein B gene of EHV-1 and EHV-4. Primers and probes were specific to each equine herpesvirus type and can be used in monoplex or multiplex PCRs, allowing the differentiation of these two closely related members of the Alphaherpesvirinae. The two probes were minor-groove binding probes (MGB) labelled with 6-carboxy-fluorescein (FAM) and VIC for detection of EHV-1 and EHV-4, respectively. Ten EHV-1 isolates, six EHV-1 positive clinical samples, one EHV-1 reference strain (EHV-1.438/77), three EHV-4 positive clinical samples, two EHV-4 isolates and one EHV-4 reference strain (EHV-4 405/76) were included in this study. EHV-1 isolates, clinical samples and the reference strain reacted in the EHV-1 real-time PCR but not in the EHV-4 real-time PCR and similarly EHV-4 clinical samples, isolates and the reference strain were positive in the EHV-4 real-time PCR but not in the EHV-1 real-time PCR. Other herpesviruses, such as EHV-2, EHV-3 and EHV-5 were all negative when tested using the multiplex real-time PCR. When bacterial pathogens and opportunistic pathogens were tested in the multiplex real-time PCR they did not react with either system. The multiplex PCR was shown to be sensitive and specific and is a useful tool for detection and differentiation of EHV-1 and EHV-4 in a single reaction. A comprehensive equine herpesvirus disease investigation procedure used in our laboratory is also outlined. This procedure describes the combination of alphaherpesvirus multiplex real-time PCR along with existing gel-based PCRs described by other authors.     

Isolation of equine herpesvirus type 5 in New Zealand

AIM: To report the first isolation of equine herpesvirus 5 (EHV-5) in New Zealand as part of a study of equine respiratory viruses in New Zealand. METHODS: Nasal swabs and peripheral blood leukocytes were collected from 114 foals and adult horses, inoculated on to equine fetal kidney, rabbit kidney and Vero cell lines and observed for cytopathic effect. EHV-5 isolates were identified using an EHV-5 specific polymerase chain reaction. All samples positive for EHV-5 were also checked for the presence of EHV-2, EHV-1 or EHV-4 DNA using published type-specific primers. The polymerase chain reaction results were further confirmed by dot blot and Southern hybridisation with specific DIG-labelled probes. RESULTS: EHV-5 was isolated from nasal swabs or peripheral blood leukocytes of 38 out of 114 horses sampled. From horses sampled more than once, EHV-5 was often isolated on more than one occasion. Most of the horses were infected with both EHV-2 and EHV-5 viruses. It was not possible to make an association between EHV-5 isolation and the presence of respiratory disease. CONCLUSION: EHV-5 is present in the New Zealand horse population. The exact role it plays in causing, or predisposing to, respiratory disease remains to be elucidated.     

A survey of respiratory viruses in New Zealand horses

AIMS: To determine which viruses circulate among selected populations of New Zealand horses and whether or not viral infections were associated with development of respiratory disease.

METHODS: Nasal swabs were collected from 33 healthy horses and 52 horses with respiratory disease and tested by virus isolation and/or PCR for the presence of equine herpesviruses (EHV) and equine rhinitis viruses.

RESULTS: Herpesviruses were the only viruses detected in nasal swab samples. When both the results of nasal swab PCR and virus isolation were considered together, a total of 41/52 (79%) horses with respiratory disease and 2/32 (6%) healthy horses were positive for at least one virus. As such, rates of virus detection were significantly higher (p<0.001) in samples from horses with respiratory disease than from healthy horses. More than half of the virus-positive horses were infected with multiple viruses. Infection with EHV-5 was most common (28 horses), followed by EHV-2 (27 horses), EHV-4 (21 horses) and EHV-1 (3 horses).

CONCLUSIONS: Herpesviruses were more commonly detected in nasal swabs from horses with respiratory disease than from healthy horses suggesting their aetiological involvement in the development of clinical signs among sampled horses. Further investigation to elucidate the exact relationships between these viruses and respiratory disease in horses is warranted.

CLINICAL RELEVANCE: Equine respiratory disease has been recognised as an important cause of wastage for the equine industry worldwide. It is likely multifactorial, involving complex interactions between different microorganisms, the environment and the host. Ability to control, or minimise, the adverse effects of equine respiratory disease is critically dependent on our understanding of microbial agents involved in these interactions. The results of the present study update our knowledge on the equine respiratory viruses currently circulating among selected populations of horses in New Zealand.     

Isolation of a gammaherpesvirus similar to asinine herpesvirus-2 (AHV-2) from a mule and a survey of mules and donkeys for AHV-2 infection by real-time PCR

Equids are commonly infected by herpesviruses, but isolation of herpesviruses from mules has apparently not been previously reported. Furthermore, the genomic relationships among the various equid herpesviruses are poorly characterized. We describe the isolation and preliminary characterization of a mule gammaherpesvirus tentatively identified as asinine herpesvirus-2 (AHV-2; also designated equid herpesvirus-7 (EHV-7)) from the nasal secretions (NS) of a healthy mule in northern California. The virus was initially identified by transmission electron microscopic examination of lysates of cell culture inoculated with NS collected from the mule. A 913 nucleotide sequence of the DNA polymerase gene was amplified using degenerate primers, and comparison of this sequence with those of various other herpesviruses showed that the mule herpesvirus was most closely related to EHV-2 (AHV-2 sequences were not available for comparison). The sequence of a shorter portion (166 nucleotides) of the mule herpesvirus DNA polymerase gene was identical to that of the published sequence of an asinine gammaherpesvirus, previously designated as AHV-4-3 (AY054992). AHV-2 was detected by real-time polymerase chain reaction assay in the NS of approximately 8% of a cohort of 114 healthy mules and 13 donkeys.     

Isolation of equine herpesvirus type 5 in New Zealand

Aim. To report the first isolation of equine herpesvirus 5 (EHV-5) in New Zealand as part of a study of equine respiratory viruses in New Zealand.

Methods. Nasal swabs and peripheral blood leukocytes were collected from 114 foals and adult horses, inoculated on to equine fetal kidney, rabbit kidney and Vero cell lines and observed for cytopathic effect. EHV-5 isolates were identified using an EHV-5 specific polymerase chain reaction. All samples positive for EHV-5 were also checked for the presence of EHV-2, EHV-1 or EHV-4 DNA using published type-specific primers. The polymerase chain reaction results were further confirmed by dot blot and Southern hybridisation with specific DIG-labelled probes.

Results. EHV-5 was isolated from nasal swabs or peripheral blood leukocytes of 38 out of 114 horses sampled. From horses sampled more than once, EHV-5 was often isolated on more than one occasion. Most of the horses were infected with both EHV-2 and EHV-5 viruses. It was not possible to make an association between EHV-5 isolation and the presence of respiratory disease.

Conclusion. EHV-5 is present in the New Zealand horse population. The exact role it plays in causing, or predisposing to, respiratory disease remains to be elucidated.     

Occurrence of Equine Coital Exanthema in Mares from an Embryo Transfer Center

Equine coital exanthema (ECE) is an acute, venereal disease caused by equid herpesvirus 3 (EHV-3), characterized by the formation of papules, vesicles, pustules, and ulcers on the vaginal and vestibular mucosa as well as on the skin of the penis, prepuce, and perineal region of mares and stallions. The present work describes an outbreak of ECE characterized by typical lesions around the anus and on the perineal skin, discomfort, and anorectal lymphadenopathy, which occurred in a large number of donor and recipient mares at an embryo transfer center in Argentina. We found that the horses' movement pattern, the environmental conditions, and the management procedures could have favored the introduction and/or reactivation from latency and spread of EHV-3. Although this is the first report of an outbreak of ECE in an embryo transfer facility, it reinforces the need to introduce additional hygienic and preventive measures to avoid EHV-3 spread and future ECE outbreaks.     

First Report on Molecular Detection of Equine Upper Respiratory Infectious Viruses in Republic of Korea

The prevalence of equine respiratory virus infections among a suspected population of race horses was examined using polymerase chain reaction (PCR). One or more of five equine respiratory viruses were detected in the nasal swabs of 45 of 89 horses (50.6%), and the detection rate of equine herpesvirus type 1 (EHV-1), equine herpesvirus type 4 (EHV-4), equine herpesvirus type 5 (EHV-5), equine rhinitis A virus (ERAV) and equine rhinitis B virus (ERBV) were 5.6%, 7.9%, 39.0%, 2.2%, and 6.7%, respectively. Among the 45 infected horses, 7 were co-infected with EHV and/or equine rhinitisvirus (ERV). Equine influenzavirus and equine arteritisvirus were not detected in any samples. Specific antibodies to EHV-1 and/or EHV-4 were detected in 59 of 73 tested sera (80.8%), using a virus neutralization test. This investigation suggests that equine respiratory viruses are endemic at Seoul Race Park and that the impact of viral infections on race horses’ health in Republic of Korea should be evaluated.     

Nasal Shedding of Equid Herpesvirus Type 1 and Type 4 in Hospitalized,Febrile Horses

The objective of this study was to determine the prevalence of shedding of equid herpesvirus 1 (EHV-1) or EHV-4 in nasal swab samples from any febrile, hospitalized horses during a 1-year period. It was hypothesized that some fevers in horses are associated with viral replication following recrudescence of latent virus or following a horizontal viral infection prior to or during admission to a referral hospital. During the observational period, nasal swab samples were collected from 64 febrile and 10 nonfebrile hospitalized horses. Routine DNA extraction was performed, and a validated quantitative polymerase chain reaction (qPCR) assay was used to detect and quantify genomic EHV-1 and -4 DNA. Genomic DNA of EHV-4 was detected in the nasal swab specimen of 1 of 64 febrile horses. EHV-1 DNA was not detected in any of the febrile horses. Samples from all nonfebrile horses were negative for both viruses. Considering the known association between fever and shedding of EHV-1 and EHV-4, we anticipated finding a higher percentage of PCR-positive samples from febrile patients. Fevers detected were likely a result of active disease processes for which the horses were hospitalized; concurrent other diseases appeared not to affect viral recrudescence. Further studies are warranted to examine frequency and factors of EHV latency and reactivation.     

Equine herpesviruses 1 (EHV-1) and 4 (EHV-4)--epidemiology, disease and immunoprophylaxis: a brief review

This review concentrates on the epidemiology, latency and pathogenesis of, and the approaches taken to control infection of horses by equine herpesvirus types 1 (EHV-1) and 4 (EHV-4). Although both viruses may cause febrile rhinopneumonitis, EHV-1 is the main cause of abortions, paresis and neonatal foal deaths. The lesion central to these three conditions is necrotising vasculitis and thrombosis resulting from lytic infection of endothelial cells lining blood capillaries. The initiation of infection in these lesions is likely to be by reactivated EHV-1 from latently infected leukocytes. However, host factors responsible for reactivation remain poorly understood. While vaccine development against these important viruses of equines involving classical and modern approaches has been ongoing for over five decades, progress, compared to other alpha herpesviruses of veterinary importance affecting cattle and pigs, has been slow. However recent data with a live temperature sensitive EHV-1 vaccine show promise.     

Viruses associated with outbreaks of equine respiratory disease in New Zealand

AIM: To identify viruses associated with respiratory disease in young horses in New Zealand. METHODS: Nasal swabs and blood samples were collected from 45 foals or horses from five separate outbreaks of respiratory disease that occurred in New Zealand in 1996, and from 37 yearlings at the time of the annual yearling sales in January that same year. Virus isolation from nasal swabs and peripheral blood leukocytes (PBL) was undertaken and serum samples were tested for antibodies against equine herpesviruses (EHV-1, EHV-2, EHV-4 and EHV-5), equine rhinitis-A virus (ERAV), equine rhinitis-B virus (ERBV), equine adenovirus 1 (EAdV-1), equine arteritis virus (EAV), reovirus 3 and parainfluenza virus type 3 (PIV3). RESULTS: Viruses were isolated from 24/94 (26%) nasal swab samples and from 77/80 (96%) PBL samples collected from both healthy horses and horses showing clinical signs of respiratory disease. All isolates were identified as EHV-2, EHV-4, EHV-5 or untyped EHV. Of the horses and foals tested, 59/82 (72%) were positive for EHV-1 and/or EHV-4 serum neutralising (SN) antibody on at least one sampling occasion, 52/82 (63%) for EHV-1-specific antibody tested by enzyme-linked immunosorbent assay (ELISA), 10/80 (13%) for ERAV SN antibody, 60/80 (75%) for ERBV SN antibody, and 42/80 (53%) for haemagglutination inhibition (HI) antibody to EAdV-1. None of the 64 serum samples tested were positive for antibodies to EAV, reovirus 3 or PIV3. Evidence of infection with all viruses tested was detected in both healthy horses and in horses showing clinical signs of respiratory disease. Recent EHV-2 infection was associated with the development of signs of respiratory disease among yearlings [relative risk (RR)=2.67, 95% CI=1.59-4.47, p=0.017]. CONCLUSIONS: Of the equine respiratory viruses detected in horses in New Zealand during this study, EHV-2 was most likely to be associated with respiratory disease. However, factors other than viral infection are probably important in the development of clinical signs of disease.     

Viruses associated with outbreaks of equine respiratory disease in New Zealand

AIM: To identify viruses associated with respiratory disease in young horses in New Zealand.

METHODS: Nasal swabs and blood samples were collected from 45 foals or horses from five separate outbreaks of respiratory disease that occurred in New Zealand in 1996, and from 37 yearlings at the time of the annual yearling sales in January that same year. Virus isolation from nasal swabs and peripheral blood leukocytes (PBL) was undertaken and serum samples were tested for antibodies against equine herpesviruses (EHV-1, EHV-2, EHV-4 and EHV-5), equine rhinitis-A virus (ERAV), equine rhinitis-B virus (ERBV), equine adenovirus 1 (EAdV-1), equine arteritis virus (EAV), reovirus 3 and parainfluenza virus type 3 (PIV3).

RESULTS: Viruses were isolated from 24/94 (26%) nasal swab samples and from 77/80 (96%) PBL samples collected from both healthy horses and horses showing clinical signs of respiratory disease. All isolates were identified as EHV-2, EHV-4, EHV-5 or untyped EHV. Of the horses and foals tested, 59/82 (72%) were positive for EHV-1 and/or EHV-4 serum neutralising (SN) antibody on at least one sampling occasion, 52/82 (63%) for EHV-1-specific antibody tested by enzyme-linked immunosorbent assay (ELISA), 10/80 (13%) for ERAV SN antibody, 60/80 (75%) for ERBV SN antibody, and 42/80 (53%) for haemagglutination inhibition (HI) antibody to EAdV-1. None of the 64 serum samples tested were positive for antibodies to EAV, reovirus 3 or PIV3. Evidence of infection with all viruses tested was detected in both healthy horses and in horses showing clinical signs of respiratory disease. Recent EHV-2 infection was associated with the development of signs of respiratory disease among yearlings [relative risk (RR)=2.67, 95% CI=1.59-4.47, p=0.017].

CONCLUSIONS: Of the equine respiratory viruses detected in horses in New Zealand during this study, EHV-2 was most likely to be associated with respiratory disease. However, factors other than viral infection are probably important in the development of clinical signs of disease.     

EHV-1 and EHV-4 infection in vaccinated mares and their foals

A silent cycle of equine herpesvirus 1 infection was described following epidemiological studies of unvaccinated mares and foals on a Hunter Valley stud farm. Following the introduction of routine vaccination with an inactivated whole virus equine herpesvirus 1 (EHV-1) and equine herpesvirus 4 (EHV-4) vaccine in 1997, a subsequent study identified excretion of EHV-1 and EHV-4 in nasal swab samples tested by PCR from vaccinated mares and their unweaned, unvaccinated foals. The current sero-epidemiological investigation of vaccinated mares and their young foals found serological evidence of EHV-1 and EHV-4 infection in mares and foals in the first 5 weeks of life. The results further support that EHV-1 and EHV-4 circulate in vaccinated populations of mares and their unweaned foals and confirms the continuation of the cycle of EHV-1 and EHV-4 infection.     

Equine respiratory viruses in foals in New Zealand

AIMS: To identify the respiratory viruses that are present among foals in New Zealand and to establish the age at which foals first become infected with these viruses. METHODS: Foals were recruited to the study in October/ November 1995 at the age of 1 month (Group A) or in March/ April 1996 at the age of 4-6 months (Groups B and C). Nasal swabs and blood samples were collected at monthly intervals. Nasal swabs and peripheral blood leucocytes (PBL) harvested from heparinised blood samples were used for virus isolation; serum harvested from whole-blood samples was used for serological testing for the presence of antibodies against equine herpesvirus (EHV)-1 or -4, equine rhinitis-A virus (ERAV), equine rhinitis-B virus (ERBV), equine adenovirus 1 (EAdV-1), equine arteritis virus (EAV), reovirus 3 and parainfluenza virus type 3 (PIV3). Twelve foals were sampled until December 1996; the remaining 19 foals were lost from the study at various times prior to this date. RESULTS: The only viruses isolated were EHV-2 and EHV-5. EHV-2 was isolated from 155/157 PBL samples collected during the period of study and from 40/172 nasal swabs collected from 18 foals. All isolations from nasal swabs, except one, were made over a period of 2-4 months from January to April (Group A), March to April (Group B) or May to July (Group C). EHV-5 was isolated from either PBL, nasal swabs, or both, from 15 foals on 32 occasions. All foals were positive for antibodies to EHV-1 or EHV-4, as tested by serum neutralisation (SN), on at least one sampling occasion and all but one were positive for EHV-1 antibodies measured by enzyme-linked immunosorbent assay (ELISA) on at least one sampling occasion. Recent EHV-1 infection was evident at least once during the period of study in 18/23 (78%) foals for which at least two samples were collected. SN antibodies to ERBV were evident in 19/23 (83%) foals on at least one sampling occasion and 15/23 foals showed evidence of seroconversion to ERBV. Antibodies to ERAV were only detected in serum samples collected from foals in Group A and probably represented maternally-derived antibodies. Haemagglutination inhibition (HI) antibody titres 1:10 to EAdV-1were evident in 21/23 (91%) foals on at least one sampling occasion and 16/23 foals showed serological evidence of recent EAdV-1 infection. None of the 67 serum samples tested were positive for antibodies to EAV, reovirus 3 or PIV3. There was no clear association between infection with any of the viruses isolated or tested for and the presence of overt clinical signs of respiratory disease. CONCLUSIONS: There was serological and/or virological evidence that EHV-1, EHV-2, EHV-5, EAdV-1 and ERBV infections were present among foals in New Zealand. EHV-2 infection was first detected in foals as young as 3 months of age. The isolation of EHV-2 from nasal swabs preceded serological evidence of infection with other respiratory viruses, suggesting that EHV-2 may predispose foals to other viral infections.     

Equine Viral Respiratory Pathogen Surveillance at Horse Shows and Sales

Equine respiratory viral infections cause significant worldwide disease and economic loss. Common causes include equine influenza virus (EIV) and equine herpesviruses-1 and -4 (EHV-1 and -4), and risk of exposure to these agents may be highest in young horses commingling at sales and competitive events. A surveillance study was conducted at two horse shows and two Thoroughbred sales to determine whether horses shed EHV-1, EHV-4, or EIV on arrival, or 2-4 days later, and whether shedding was associated with identifiable risk factors. Real-time polymerase chain reaction assays were used to detect EHV-1, EHV-4, and EIV nucleic acid in nasal swabs obtained from 369 horses at the four events. In response to evidence of clinical disease, 82 additional horses were sampled at two farms providing horses for one of the sales. On arrival at the events, shedding of EHV-1 was detected in 3.3%, EHV-4 in 1.1%, and EIV in 0.8% of horses. EHV-1 was detected at low levels, and EHV-1 and EHV-4 detection was not associated with clinical disease. EIV was detected only in horses at a Thoroughbred sale, in association with an outbreak of respiratory disease traced back to regional farms. On arrival at events, horses younger than 2 years had a significantly greater risk of shedding EHV-1 compared with older horses; no other significant risk factors associated with viral shedding were identified. Thus, there is a risk of exposure to EIV, EHV-1, and EHV-4 at equine events, and horses and events should be managed to mitigate this risk.