Prevalence of Nasal Shedding of Equid Gammaherpesviruses in Healthy Swiss Horses

Equid Gamma herpesvirus (eGHV) infections have been reported worldwide and may be correlated with clinical signs, e.g., affecting the respiratory tract in young horses. eGHV are shed by healthy horses as well as horses with respiratory tract disease. The prevalence in healthy Swiss horses is unknown to date but this data would provide valuable information for causal diagnosis in clinical cases and formulation of biosecurity recommendations. Nasal swabs from 68 healthy horses from 12 Swiss stables and 2 stables near the Swiss border region in Germany were analyzed by panherpes nested PCR. Positive samples were sequenced. A multivariable model was used to determine if sex, age, breed, canton, or stable had a significant effect on the shedding status of each detected eGHV. Overall, the eGHV prevalence was 59% (n = 68); the prevalence for equid herpesvirus-2 (EHV-2), equid herpesvirus-5 (EHV-5) and asinine herpesvirus-5 (AHV-5) was 38%, 12% and 9%, respectively. Co-infections with multiple eGHVs were observed in 25% of the positive samples. The odds of shedding EHV-2 decreased with age (p = 0.01) whereas the odds of shedding AHV-5 increased with age (p = 0.04). Breed, sex, canton, or stable had no significant association with eGHV shedding. As EHV-2 shedding was common in healthy horses a positive PCR result must be interpreted with caution regarding the formulation of biosecurity recommendations and causal diagnosis. As EHV-5 and AHV-5 shedding was less common than EHV-2, a positive test result is more likely to be of clinical relevance. Shedding of multiple eGHV complicates the interpretation of positive test results in a horse.

Molecular Detection and Genetic Characteristics of Equine Herpesvirus in Korea

Respiratory diseases cause significant economic losses (especially in the horse racing industry). The present study describes the detection and genetic characteristics of equine herpesvirus (EHV) from a total of 1497 samples from clinically healthy horses in Korea, including 926 blood samples, 187 lung tissues, and 384 nasal swabs. EHV-2 and EHV-5 were detected in 386 (41.7%; 95% CI: 38.5–44.9) and 201 (21.7%; 95% CI: 19.1–24.4) blood samples, respectively, and in 25 (13.4%; 95% CI: 8.5–18.2) and 35 (18.7%; 95% CI: 13.1–24.3) lung tissues, respectively. EHV-1 and EHV-4 were not detected in either blood or lung tissues. EHV-1, EHV-2, and EHV-5 were detected in 46 (12.0%; 95% CI: 8.7–15.2), 21 (5.5%; 95% CI: 3.2–7.7), and 43 (11.2%; 95% CI: 8.0–14.4) nasal swabs, respectively. EHV-4 was not detected in nasal swabs. Co-infection with EHV-2 and EHV-5 was detected in 11.6% (107/926) of the blood samples and 6.4% (12/187) of lung tissues. In nasal swabs, co-infection with EHV-1, EHV-2, and EHV-5 was detected in 0.8% (3/384) of samples. Phylogenetic analysis of the glycoprotein B gene showed that EHV-1, EHV-2, and EHV-5 strains demonstrated significant genetic diversity in Korea, with a nucleotide sequence identity among them that ranged from 95.7% to 100% for EHV-1, 96.2–100% for EHV-2, and 93.8–99.3% for EHV-5. These results are the first phylogenetic analyses of EHV-1 in Korea in nasal swabs from a nationwide population of clinically healthy horses. Both EHV-2 and EHV-5 from blood, lung tissues, and nasal swabs were also detected.

Detection of Equid gammaherpesvirus 2 and 5 DNA in the upper respiratory tract of asymptomatic horses from Southern Brazil

Equid gammaherpesvirus 2 (EHV-2) and 5 (EHV-5) are members of the Herpesviridae family and have been reported in horse populations worldwide. This study aimed to evaluate the presence of herpesvirus DNA in the upper respiratory tract of horses. Twenty-six nasal swabs were collected from asymptomatic adult horses of two different horse farms (A, n = 18; B, n = 8), both located in Southern Brazil. The EHV-1, EHV-2, EHV-4, and EHV-5 DNA analyses were performed using nested PCR assays targeting the glycoprotein B gene. Four (15.3%) and 12 (46.1%) of the 26 nasal swab samples were positive for the EHV-2 and EHV-5, respectively. Four (15.3%) horses were detected with both viruses simultaneously. DNA of EHV-2 and EHV-5 in both single and mixed infections was identified in horses from both herds. All swab samples were negative for EHV-1 and EHV-4. This study reports the first detection of EHV-2 and EHV-5 in the upper respiratory tracts of horses in Brazil. The high detection rate of EHV-2 and EHV-5 in asymptomatic adult horses demonstrates that these gammaherpesviruses are circulating in Brazil.

The Molecular Detection of Equine Herpesviruses 2 and 5 in Genital Swabs From Clinically Normal Thoroughbred Mares in South Korea

Equine herpesvirus (EHV) 2 and equine herpesvirus 5 (EHV-5) have been getting attention as potential causative pathogens of reproductive disorders in horses. Equine herpesviruses 2 and 5 are widespread among horses and have been detected in various samples including nasal swabs, blood, and ocular swabs. However, the detection of these pathogens in genital swabs has not been determined. The aims of this study were to determine the positive rate of EHV-2 and EHV-5 DNA in genital swabs taken from clinically normal mares and to define the genetic diversity of these EHV-2 and EHV-5 DNA sequences by comparing them to previously reported EHV-2 and EHV-5 nucleotide sequences. Four hundred and thirty genital swabs from clinically normal mares were tested for EHV-2 and EHV-5 by glycoprotein B (gB)-specific polymerase chain reaction. From 430 genital swabs, 10 (2.3%) contained EHV-2 DNA, and 11 (2.6%) were positive for EHV-5. The sequences of the EHV-2 and EHV-5 gB gene were used in phylogenetic analyses and revealed that the Korean EHV-2 and EHV-5 strains have a marked genetic diversity, with a nucleotide sequence identity among the strains that ranged from 92.57% to 100% and from 98.07% to 100% for EHV-2 and EHV-5, respectively. The degree of similarity between Korean strains and those recovered from horses elsewhere ranged from 88.13% to 100% for EHV-2 and 95.96% to 100% for EHV-5. Further studies are now required to determine if the presence of EHV-2 and EHV-5 DNA is associated with reproductive disorders in clinically affected horses.

Prevalence and sequence analysis of equid herpesviruses from the respiratory tract of Polish horses

Background

Equid herpesviruses (EHVs) are widespread in equine populations worldwide. While the infection with equine α-herpesviruses (EHV-1 and EHV-4) has been linked to several clinical outcomes, the pathogenic potential for equine γ-herpesviruses (EHV-2 and EHV-5) is still unclear. The objective of the current study was to determine the prevalence of infection with EHVs among Polish horses, to investigate factors associated with EHV infections among horses sampled, and to determine genetic variability within Polish EHV-2 isolates.

Methods

Virus-specific real-time PCR assays were used for detection of EHV-1, EHV-2, EHV-4 and EHV-5 in nasal swabs collected from 540 horses from 13 national horse studs located throughout Poland. A proportion of EHV-2/5 positive samples were subjected to virus isolation followed by amplification and analysis of partial glycoprotein B sequence.

Results

Overall, 448/540 (83.0%) horses sampled were positive for at least one virus. The most prevalent was infection with EHV-2 (77.2%), followed by EHV-5 (47.0%), and EHV-4 (0.4%). None of the horses was positive for EHV-1. Approximately half of the virus-infected horses were positive for both EHV-2 and EHV-5. The proportion of EHV-2/5 positive horses varied by age, breed, and season. Only 8.0% of horses sampled, mostly Arabians, showed clinical signs of respiratory disease at the time of sampling. The viral load of both EHV-2 and EHV-5 DNA was highest in swabs from young horses, which was particularly evident for EHV-2 infected foals. Mean viral loads in nasal swabs collected from diseased horses were higher than in swabs from healthy horses. That was also true for EHV-2 when only diseased Arabian foals were considered, but the levels of EHV-5 DNA were lower in swabs from diseased than from healthy foals. In agreement with other studies, there was a considerable variability between Polish EHV-2 sequences, with no clustering of sequences from horses with different health status. The level of EHV-2 variability seemed to differ between different studs/breeds.

Conclusions

The presence of foals and yearlings on a property is likely to increase the risk of active EHV-2/5 infection among in-contact horses. The existence of breed-specific differences in susceptibility to EHV-2/5 infections should be further investigated, as it may provide one variable that needs to be considered in attempts to associate EHV-2/5 infections with disease. Overall, the data presented add to the existing knowledge of the epidemiology and biology of equine γ-herpesviruses, with the long-term goal of better understanding of the pathogenesis and the impact of infections with these viruses on the well-being of the horse.

Antiherpetic Drugs in Equine Medicine

Since vaccination may not prevent disease, antiherpetic drugs have been investigated for the therapy of several equine herpesviruses. Drug efficacy has been assessed in horses with disease, but most evidence is in vitro, in other species, or empirical. Oral valacyclovir is most often administered in the therapy of equine herpesvirus type-1 (EHV-1) to protect adult horses from equine herpesvirus myeloencephalopathy, while oral acyclovir is frequently administered for EHV-5 infection in the therapy of equine multinodular pulmonary fibrosis. Other antiherpetic drugs are promising but require further investigation. Several topical drugs are also empirically used in the therapy of equine viral keratitis.

Development and application of a quantitative PCR assay to study equine herpesvirus 5 invasion and replication in equine tissues in vitro and in vivo

Equine herpesvirus 5 (EHV-5) infection is associated with pulmonary fibrosis in horses, but further studies on EHV-5 persistence in equine cells are needed to fully understand viral and host contributions to disease pathogenesis. Our aim was to develop a quantitative PCR (qPCR) assay to measure EHV-5 viral copy number in equine cell cultures, blood lymphocytes, and nasal swabs of horses. Furthermore, we used a recently developed equine primary respiratory cell culture system to study EHV-5 pathogenesis at the respiratory tract. PCR primers and a probe were designed to target gene E11 of the EHV-5 genome. Sensitivity and repeatability were established, and specificity was verified by testing multiple isolates of EHV-5, as well as DNA from other equine herpesviruses. Four-week old fully differentiated (mature), newly seeded (immature) primary equine respiratory epithelial cell (ERECs), and equine dermal cell cultures were inoculated with EHV-5 and the cells and supernatants collected daily for 14days. Blood lymphocytes and nasal swabs were collected from horses experimentally infected with equine herpesvirus 1 (EHV-1). The qPCR assay detected EHV-5 at stable concentrations throughout 14days in inoculated mature EREC and equine dermal cell cultures (peaking at 202 and 5861 viral genomes per 10⁶ cellular β actin, respectively). EHV-5 copies detected in the immature EREC cultures increased over 14days and reached levels greater than 10,000 viral genomes per 10⁶ cellular β actin. Moreover, EHV-5 was detected in the lymphocytes of 76% of horses and in the nasal swabs of 84% of horses experimentally infected with EHV-1 pre-inoculation with EHV-1. Post-inoculation with EHV-1, EHV-5 was detected in lymphocytes of 52% of horses while EHV-5 levels in nasal swabs were not significantly different from pre-inoculation levels. In conclusion, qPCR was a reliable technique to investigate viral load in in vivo and in vitro samples, and EHV-5 replication in equine epithelial cells may be influenced by cellular stages of differentiation.

Keratoconjunctivitis in a group of Icelandic horses with suspected γ-herpesvirus involvement

REASONS FOR PERFORMING STUDY

The role of equid γ-herpesviruses on ocular surface diseases has been disputed, because the diagnosis is usually based on clinical symptoms and detection of viral DNA from samples obtained from live animals.

OBJECTIVES

To describe the clinical course, results of polymerase chain reaction (PCR) analysis, in situ hybridisation, cell culture and pathohistological findings of select cases in a presumed outbreak of herpesvirus infection in a group of 15 Icelandic horses.

STUDY DESIGN

Case series.

METHODS

Pooled ocular and nasal swabs and peripheral blood mononuclear cells of horses diagnosed clinically with herpesvirus-associated keratoconjunctivitis were analysed for presence of equine herpesviruses (EHV)-2 and EHV-5 nucleic acid using real-time PCR. Necropsy specimens from one horse, subjected to euthanasia due to deterioration of clinical symptoms were examined histopathologically, and analysed for presence of EHV-2 and EHV-5 nucleic acid using real-time PCR. In situ hybridisation and cell culture of select samples were performed.

RESULTS

All horses with symptoms of severe keratoconjunctivitis were positive for presence of either EHV-2 and/or EHV-5 nucleic acid using real-time PCR. Assessment of necropsy specimens of the most severely affected case, revealed presence of EHV-2 and/or EHV-5 nucleic acid in several ocular and extraocular anatomical locations. The remaining horses responded favourably to symptomatic treatment.

CONCLUSIONS

This case series illustrates a severe outbreak of keratoconjunctivitis in a group of Icelandic horses, with suspected γ-herpesvirus involvement. For the first time equid γ-herpesviruses were detected in intraocular anatomical locations.

Detection of Equid herpesvirus type 2 and 5 DNA in uterine flushings of mares with reproductive disorders

In recent years, there has been increasing evidence of the potential pathogenic significance of equine gammaherpesviruses in the horse. In humans, cattle and mice, gammaherpesviruses have already been associated with uterine infection. The aim of the present study was to investigate the presence of gammaherpesviruses in uterine flushings of mares with reproductive problems and to evaluate if there was a possible statistical association with clinical and laboratory findings in these cases. A total of 80 uterine flushings were collected from 61 mares with different reproductive problems and these were tested for equine herpesviruses (EHV) 1-5 by PCR. In the case of each mare in the study, the age, history of infertility, presence of anatomical defects in the reproductive tract, presence of systemic or local disease at time of sampling, phase in the oestrous cycle, post-partum interval, nature of uterine lavage performed (low versus large volume lavage), cytological and bacteriological examination results from the uterine flushing, and PCR herpesvirus results were recorded. Univariate analysis and multivariable logistic regression models were used to identify possible statistical associations and risk factors. Nine out of 61 mares (14.7%) had EHV-5 DNA in their uterine flushings. Co-infections with EHV-1 and EHV-2 were present in two cases. Of all the variables analyzed, only the cytological examination findings were associated with EHV-5 PCR positive results, both on univariate and multivariable analysis, especially in cases with an inflammation score of 3. It is postulated that presence of EHV-5 infection in the non-pregnant uterus may have a role to play in reproductive dysfunction and have a negative consequence on the pregnant uterus. Additional studies involving both healthy mares and mares with reproductive problems need to be performed, however, to elucidate whatever role equine gammaherpesviruses may play in the reproductive tract. This would be very worthwhile, since reproductive problems can have a significant impact on the equine breeding industry. Gaining a greater understanding of its causes could lead to new approaches for prevention and treatment.

Detection and quantitation of equid gammaherpesviruses (EHV-2, EHV-5) in nasal swabs using an accredited standardised quantitative PCR method

Equid gammaherpesviruses-2 and -5 are involved in respiratory problems, with potential clinical manifestations such as nasal discharge, pharyngitis and swollen lymph nodes. These viruses are sometimes associated with a poor-performance syndrome, which may result in a significant and negative economic impact for the horse industry. The aim of the present study was to develop and validate quantitative PCR methods for the detection and quantitation of EHV-2 and EHV-5 in equine respiratory fluids. Two distinct tests were characterised: (a) for the qPCR alone and (b) for the whole method (extraction and qPCR) according to the standard model AFNOR XP U47-600-2 (viz., specificity, quantifiable sensibility, linearity, accuracy, range of application, trueness, precision, repeatability and precision of reproducibility). EHV-2 and EHV-5 detection were performed on nasal swabs collected from 172 horses, all of which exhibited clinical signs of respiratory disease. The data revealed a high rate of EHV-2/EHV-5 co-detection that was correlated significantly with age. Viral load of EHV-2 was significantly higher in young horses whereas viral load of EHV-5 was not significantly different with age.

Equine gammaherpesviruses: perfect parasites?

The evolutionary success of the equine gammaherpesviruses (GHVs) is demonstrated by their consistent and widespread presence in horse populations worldwide. Equine GHVs establish infection in young foals and can be continually detected over the lifetime of the host either by recrudescence of latent infections or by re-infection. A definitive diagnosis of clinical disease in horses due to GHV infection remains challenging given the ubiquitous nature of the GHVs in horses without clinical signs, as well as in horses with clinical signs ranging from mild respiratory disease to severe equine multinodular pulmonary fibrosis. This review aims to examine what is known about equine GHV and explore the balance of the relationship that has evolved over millions of years between these viruses and their host.