Viral testing of 10 cases of Theiler's disease and 37 in-contact horses in the absence of equine biologic product administration: A prospective study (2014-2018)

Subclinical infection and potential shedding routes of equine parvovirus-hepatitis among hospitalized horses in Austria

BACKGROUND

Equine parvovirus hepatitis (EqPV-H) can cause Theiler's disease and subclinical hepatitis in horses.

OBJECTIVES

Assess the frequency of subclinical EqPV-H infection in hospitalized horses and to study viral transmission by investigating potential shedding routes.

ANIMALS

One hundred sixteen equids, that presented to the University Equine Hospital of the University of Veterinary Medicine Vienna between February 2021 and March 2022, for causes other than hepatopathy.

METHODS

In this cross-sectional study, samples (serum, feces, nasal, and buccal swabs) of hospitalized horses were collected. Sera were screened for the presence of anti-EqPV-H antibodies by a luciferase immunoprecipitation system assay. Quantitative PCR was used for the detection of EqPV-H DNA in the samples and a nested PCR was used for further validation.

RESULTS

Seroprevalence was 10.3% (12/116) and viremia occurred in 12.9% (15/116) of the serologically positive horses. The detected viral load in serum varied from non-quantifiable amount to 1.3 × 106 genome equivalents per milliliter of serum. A low viral load of EqPV-H DNA was detected in 2 nasal swabs and 1 fecal sample.

CONCLUSION AND CLINICAL IMPORTANCE

EqPV-H DNA was detected in nasal secretions and feces of viremic horses, which could pose a risk to naive hospitalized horses. It is advisable to screen hospitalized horses that are potential donors of blood or plasma to reduce the risk of iatrogenic EqPV-H transmission.

Detection of Equine Parvovirus-Hepatitis Virus and Equine Hepacivirus in Archived Sera from Horses in France and Australia

Reports of newly discovered equine hepatotropic flavi- and parvoviruses have emerged throughout the last decade in many countries, the discovery of which has stimulated a great deal of interest and clinical research. Although commonly detected in horses without signs of disease, equine parvovirus hepatitis (EqPV-H) and equine hepacivirus (EqHV) have been associated with liver disease, including following the administration of contaminated anti-toxin. Our aim was to determine whether EqPV-H and EqHV are present in Australian horses and whether EqPV-H was present in French horses and to examine sequence diversity between strains of both viruses amongst infected horses on either side of the globe. Sera from 188 Australian horses and 256 French horses from horses with and without clinical signs of disease were collected. Twelve out of 256 (4.7%) and 6 out of 188 (3.2%) French and Australian horses, respectively, were positive for the molecular detection of EqPV-H. Five out of 256 (1.9%) and 21 out of 188 (11.2%) French and Australian horses, respectively, were positive for the molecular detection of EqHV. Australian strains for both viruses were genomically clustered, in contrast to strains from French horses, which were more broadly distributed. The findings of this preliminary survey, with the molecular detection of EqHV and EqPV-H in Australia and the latter in France, adds to the growing body of awareness regarding these recently discovered hepatotropic viruses. It has provided valuable information not just in terms of geographic endemicity but will guide equine clinicians, carers, and authorities regarding infectious agents and potential impacts of allogenic tissue contamination. Although we have filled many gaps in the world map regarding equine hepatotropic viruses, further prospective studies in this emerging field may be useful in terms of elucidating risk factors and pathogenesis of these pathogens and management of cases in terms of prevention and diagnosis.

Naturally acquired equine parvovirus-hepatitis is associated with a wide range of hepatic lesions in horses

Equine parvovirus-hepatitis (EqPV-H) is the causative agent of Theiler's disease, or severe acute hepatic necrosis, in horses. However, it is poorly understood whether EqPV-H is associated with other histologic findings in horses with clinical liver disease. The objective of this study was to examine the prevalence and severity of EqPV-H infections in diagnostic liver samples. Archived formalin-fixed, paraffin-embedded (FFPE) liver samples (n = 98) from Cornell University and University of California, Davis, collected between 2007 and 2022 were evaluated for 15 individual histologic features and by EqPV-H in situ hybridization. EqPV-H was detected in 48% (n = 47) of samples. The most common histologic features of EqPV-H-positive samples included individual hepatocyte death (n = 40, 85%), lobular infiltrates (n = 38, 80%), portal infiltrates (n = 35, 74%), and ductular reaction (n = 33, 70%). Centrilobular necrosis, portal infiltrate, and individual hepatocyte death were positively associated with high viral load. Neutrophil infiltrates, bridging fibrosis, and portal edema were negatively associated with a high viral load. Only 4 of 49 tested samples were positive for equine hepacivirus by polymerase chain reaction (PCR), but the PCR assay was unreliable for FFPE tissues. In summary, this study demonstrates that EqPV-H is common in a variety of liver pathologies and should be considered as a differential diagnosis in cases of hepatitis other than Theiler's disease.

Prevalence of equine parvovirus-hepatitis in healthy broodmares in Ontario, Canada

Equine parvovirus-hepatitis (EqPV-H) was first reported from the serum and liver tissue of a horse diagnosed with Theiler's disease in the United States in 2018. Theiler's disease, also known as equine serum hepatitis, is a severe hepatitis with fulminant hepatic necrosis. The disease has most frequently been reported following the administration of equine-origin biological products; however, it has also been reported in in-contact horses with no prior biologic administration. EqPV-H has been detected in clinically healthy horses in North America (USA, Canada), Europe (Germany, Austria, Slovenia), Asia (China, South Korea), and South America (Brazil). Previous prevalence studies conducted worldwide have shown the presence of EqPV-H DNA in serum or plasma ranging from 3.2 to 19.8%. This study investigated the prevalence of EqPV-H DNA in 170 healthy broodmares of various breeds located on 37 farms in southern Ontario, Canada. The occurrence of EqPV-H infection was determined by quantitative PCR for EqPV-H DNA in serum samples. The effects of age, breed, season, pregnancy status, and equine herpesvirus-1 (EHV-1) vaccination history on EqPV-H status were also investigated. There was a prevalence of 15.9% (27/170) with viral loads of EqPV-H ranging from detectable to 2900 copies/mL. Statistical analysis showed that increasing age was a significant factor in the detection of EqPV-H DNA. Neither breed, season, pregnancy status, nor EHV-1 vaccination history was significant in predicting EqPV-H infection status.

A seasonal idiopathic hepatitis syndrome in horses presented to a Midwestern veterinary teaching hospital

OBJECTIVE

To report history, clinical examination findings, clinicopathologic findings, diagnostic test results, treatment, and outcome in horses with a novel idiopathic hepatitis syndrome.

ANIMALS

13 client-owned horses.

PROCEDURES

Medical records of horses that were presented with fever and increased blood liver enzyme activity over a 16-month period were reviewed (December 1, 2020, to April 1, 2022). Collected data included signalment, history, clinical and clinicopathologic findings, diagnostic test results, treatment, clinical progression, and short-term outcome.

RESULTS

Affected horses were presented between December and April of each of the 2 seasons investigated. The majority of horses developed cyclic fevers over the course of 3 weeks, during which time histologic evidence of hepatitis was observed. Histologic lesions included hepatic necrosis, neutrophilic to lymphohistiocytic inflammation, biliary epithelial injury, and portal fibrosis. Systemic inflammation was evidenced by increased serum amyloid A concentration and leukon changes. No horse developed signs of hepatic insufficiency, and all horses clinically recovered. Return of serum activity of GGT to within the reference range occurred within 16 weeks in most horses. Histologic lesions remained evident up to 27 weeks after initial presentation in 1 horse.

CLINICAL RELEVANCE

Although an etiologic agent has not been identified, an apparently seasonal equine hepatitis syndrome was characterized by fever, systemic inflammation, increased liver enzyme activity, and histologic evidence of hepatitis. An infectious cause is suspected on the basis of histology and outcome.

Prevalence and pathology of equine parvovirus-hepatitis in racehorses from New York racetracks

BACKGROUND

Theiler's disease, a.k.a. equine serum hepatitis, is a devastating, highly fatal disease of horses. Equine parvovirus-hepatitis (EqPV-H) has been identified as the likely cause of this disease. While the incidence of Theiler's disease is low, the prevalence of EqPV-H DNA in horses is high, with up to 37% in some regions, suggesting that subclinical or persistent infection is common.

METHODS

To determine the prevalence and pathogenicity of EqPV-H infection at New York racetracks, DNA was extracted from archived formalin-fixed, paraffin-embedded liver tissues from racehorses submitted for necropsy to the Animal Health Diagnostic Center as part of the New York State Gaming Commission-Cornell University postmortem examination program. A total of 191 liver samples from horses between 2 and 13 years old were evaluated. Extracted DNA was tested for EqPV-H using PCR and gel electrophoresis. PCR-positive samples were further assessed for tissue morphology using histology and detection of viral nucleic acid using in situ hybridization.

RESULTS

Forty-two samples were PCR positive (22%). Of those, 31 samples had positive viral nucleic acid hybridization in hepatocytes with 11 samples showing positive hybridization in necrotic hepatocytes associated with inflammatory cells, indicating active hepatitis. Both individual hepatocyte necrosis and hepatitis were positively associated with EqPV-H detection (p < 0.0001 and p = 0.0005, respectively).

CONCLUSION

These findings indicate that presence of EqPV-H in the liver and parvoviral-associated hepatitis are prevalent in racehorses from New York racetracks, thus warranting additional studies examining potential associations between EqPV-H infection and racehorse performance.

Nasal transmission of equine parvovirus hepatitis

BACKGROUND

Equine parvovirus hepatitis (EqPV-H) is highly prevalent and causes subclinical to fatal hepatitis, which can occur in outbreaks. Whereas iatrogenic transmission is well documented, the mode of horizontal transmission is not known. The virus is shed in nasal, oral and fecal secretions, and PO transmission has been reported in a single horse.

HYPOTHESIS/OBJECTIVE

Investigate the efficiency of PO and nasal transmission of EqPV-H in a larger cohort.

METHODS

Prospective experimental transmission study. Eleven EqPV-H-negative horses were inoculated with 5 × 10⁶ genome equivalents EqPV-H. Serum PCR and serology for EqPV-H were performed weekly and monthly, respectively. Horses first were inoculated PO, and then intranasally 8 weeks later.

RESULTS

No horse became viremic or seroconverted within 8 weeks after PO inoculation. After intranasal inoculation, 5 horses became viremic within 6 to 12 weeks and seroconverted within 10 to 19 weeks. After a period without monitoring from 12 to 19 weeks postinoculation, another 5 horses were found to be viremic at 19 to 22 weeks. The second set of 5 horses could have been infected by horizontal transmission from the first 5 because of cohousing.

CONCLUSIONS AND CLINICAL IMPORTANCE

We demonstrated that EqPV-H can be transmitted nasally. The prolonged eclipse phase before detectable viremia indicates biosecurity measures to control spread could be impractical.

Infection of young foals with Equine Parvovirus-Hepatitis following a fatal non-biologic case of Theiler's disease

Theiler's disease (TD) is a (sub-)acute hepatitis in adult horses and one of the most common causes of acute hepatic failure. Recent findings indicate that equine parvovirus hepatitis (EqPV-H) likely causes TD and that its transmission occurs via iatrogenic and/or natural routes. Following the death of an EqPV-H positive mare with TD, close-contact mares and foals in the same paddock were monitored to evaluate if there was any evidence of EqPV-H. For this purpose, the serum of close contact horses was examined 6 and 42 days after the mare's death for the presence of EqPV-H DNA and changes in liver-associated serum biochemical parameters. The foals had higher EqPV-H viral loads than the mares. Apart from the mare that was euthanized, none of the horses included in this study showed signs of severe disease and nor did they have particularly elevated liver enzymes. Nucleotide sequence analysis revealed no major differences between the viral DNA detected in the serum of the dead mare and any of the in-contact horses. In conclusion, our data confirmed previous findings that horizontal transmission of EqPV-H may occur through close contact between horses.

Blood Transfusion in Equids—A Practical Approach and Review

Simple Summary

Transfusion medicine is an accessible, technically simple, and often lifesaving tool that can be used in both field and hospital settings, in cases of significant bleeding or anemia. A thorough understanding of the indications, methodology and complications of blood transfusion allows the practitioner to identify cases where administration of whole blood is necessary, and how to safely perform the transfusion. This review collects the current literature surrounding blood transfusion into one readily accessible document to allow clinicians a comprehensive understanding of all aspects of equine blood transfusion, while serving as a reference for performing these procedures.

Abstract

Transfusion medicine is a crucial part of equine intensive and critical care. Blood transfusions can save lives in both acute and chronic cases of anemia, hemorrhage, and hemolysis. It is vital to have a comprehensive theoretical and practical understanding of the techniques, implications, risks, and complications. This review covers the physiology and pathophysiology of conditions requiring transfusion, as well as step by step guidance for practitioners of all experience levels. This review is designed to serve as a practical reference for those who are treating horses in either the field or hospital setting. It aims to provide both theoretical background and easy to locate formulae with guidance that is easy to refer to in a critical situation. When risks and benefits are well understood, these techniques can be confidently employed in critical situations to improve outcomes and save lives.

The history of Theiler's disease and the search for its aetiology

Theiler's disease (serum hepatitis) may occur in outbreaks or as single cases of acute hepatitis and is often associated with prior administration of equine-origin biologics approximately 4-10 weeks before the onset of clinical signs. Cases have also been described without any prior administration of blood products. The clinical disease has a low morbidity but high mortality and only adult horses are affected. The course of the disease is short, with horses either dying or completely recovering in a few days. Pathology in affected horses is predominantly centrilobular hepatocyte necrosis with mononuclear cell infiltration of the lesser affected periportal regions of the liver. Subclinical cases of the disease also occur. Based on the epidemiology and pathology of the disease, a viral cause, similar to hepatitis B in humans, has long been suspected. This paper reviews both historical and recent findings on Theiler's disease. Reported epidemics of Theiler's disease in the early 1900s are reviewed, along with their similarities to outbreaks of serum hepatitis in humans following yellow fever virus vaccinations in the 1930s and 1940s. Recent metagenomics-based studies to determine the aetiology of Theiler's disease are discussed, along with both clinical and experimental findings supporting equine parvovirus-hepatitis (EqPV-H) as the likely cause of this 100-year-old disease.

Human Pegivirus Type 1: A Common Human Virus That Is Beneficial in Immune-Mediated Disease?

Two groups identified a novel human flavivirus in the mid-1990s. One group named the virus hepatitis G virus (HGV) and the other named it GB Virus type C (GBV-C). Sequence analyses found these two isolates to be the same virus, and subsequent studies found that the virus does not cause hepatitis despite sharing genome organization with hepatitis C virus. Although HGV/GBV-C infection is common and may cause persistent infection in humans, the virus does not appear to directly cause any other known disease state. Thus, the virus was renamed “human pegivirus 1” (HPgV-1) for “persistent G” virus. HPgV-1 is found primarily in lymphocytes and not hepatocytes, and several studies found HPgV-1 infection associated with prolonged survival in people living with HIV. Co-infection of human lymphocytes with HPgV-1 and HIV inhibits HIV replication. Although three viral proteins directly inhibit HIV replication in vitro, the major effects of HPgV-1 leading to reduced HIV-related mortality appear to result from a global reduction in immune activation. HPgV-1 specifically interferes with T cell receptor signaling (TCR) by reducing proximal activation of the lymphocyte specific Src kinase LCK. Although TCR signaling is reduced, T cell activation is not abolished and with sufficient stimulus, T cell functions are enabled. Consequently, HPgV-1 is not associated with immune suppression. The HPgV-1 immunomodulatory effects are associated with beneficial outcomes in other diseases including Ebola virus infection and possibly graft-versus-host-disease following stem cell transplantation. Better understanding of HPgV-1 immune escape and mechanisms of inflammation may identify novel therapies for immune-based diseases.

Hepatic Enzyme Profile in Horses

For diagnostic purposes, liver enzymes are usually classified into hepatocellular and cholestatic. These two groups of equine liver-specific enzymes include sorbitol dehydrogenase (SDH), glutamate dehydrogenase (GLDH), γ-glutamyl transferase (GGT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and alkaline phosphatase (ALP). SDH and GLDH mostly reflect hepatocellular injury and cholestasis, while GGT expresses high values in biliary necrosis or hyperplasia. Likewise, AST, LDH, and ALP also reflect hepatocellular and biliary disease, but these enzymes are not liver specific. From the clinical point of view of the course of liver or biliary disease, AST and ALP are indicative of chronic disease, whereas SDH, GGT, and GLDH indicate an acute course. The patterns of enzymatic changes at the blood level are associated with different types of liver pathologies (infectious, inflammatory, metabolic, toxic, etc.). Increases in hepatocellular versus biliary enzyme activities are indicative of a particular process. There are different ways to diagnose alterations at the hepatic level. These include the evaluation of abnormalities in the predominant pattern of hepatocellular versus cholestatic enzyme abnormalities, the mild, moderate, or marked (5−10-fold or >10-fold) increase in enzyme abnormality concerning the upper limit of the reference range, the evolution over time (increase or decrease) and the course of the abnormality (acute or chronic).

Molecular Prevalence of Equine Parvovirus-Hepatitis in the Sera of Clinically Healthy Horses in South Korea

Equine parvovirus-hepatitis (EqPV-H) causes equine hepatitis. The prevalence of EqPV-H in healthy horses has been reported in the United States, China, Germany, and Austria. The present study determined the prevalence of EqPV-H in the sera of clinically healthy horses in South Korea to identify the potential factors for infection and examine the genetic diversity of EqPV-H DNA sequences through comparison with foreign strains. Serum samples collected from 321 horses were tested for EqPV-H using non-structural protein 1 (NS1)-specific polymerase chain reaction. The associations of EqPV-H infection with sex, age, aspartate aminotransferase and γ-glutamyl transferase levels, and race performance were analyzed. Fourteen samples tested positive for EqPV-H (4.4%, 14/321), and EqPV-H infection was associated with sex (p = 0.006) and performance (p = 0.049). In both EqPV-H-positive and control horses, liver-specific biochemical analytes were within the normal ranges. Phylogenetic analyses based on the partial sequences of EqPV-H NS1 revealed that the Korean EqPV-H isolates shared approximately 98.7-100% similarity. Of these, 11 Korean isolates shared high similarity with strains from the United States, Germany, and China, and the remaining three strains were distinct in phylogenetic analyses. The present study describes the current molecular prevalence, potential risk factors, and genetic diversity of Korean EqPV-H.

First Detection and Genetic Characterization of New Equine Parvovirus Species Circulating among Horses in Korea

Equine parvovirus-cerebrospinal fluid (EqPV-CSF) and eqcopivirus (EqCoPV) are new parvovirus species (EqPVs) identified from various tissues (CSF, blood, and respiratory swabs) in horses with neurologic and respiratory diseases. In this study, we described the prevalence rate of EqPV-CSF and EqCoPV in 133 and 77 serum and fecal samples, respectively, using polymerase chain reaction. Further, we analyzed the potential risk factors for infection. We calculated the nucleotide and amino acid similarity and constructed phylogenetic trees. There was a moderate-to-high prevalence rate (EqPV-CSF: 3.8%; EqCoPV 9.8%) of each virus in serum; moreover, age, country of foaling, and clinical colic signs were significantly associated with the EqPVs infection. The newly identified EqPV-CSF/EqCoPV genomes had high nucleotide and amino acid identities with previously isolated strains in the USA. In phylogenetic analysis, they clustered and formed a new subgroup in the genus Copiparvovirus. To our knowledge, this is the first field epidemiologic study on EqPV-CSF and EqCoPV using both serum and fecal samples. Our findings demonstrate the risk factors for infection and could facilitate the development of disease prevention strategies.

Small but mighty: old and new parvoviruses of veterinary significance

In line with the Latin expression "sed parva forti" meaning "small but mighty," the family Parvoviridae contains many of the smallest known viruses, some of which result in fatal or debilitating infections. In recent years, advances in metagenomic viral discovery techniques have dramatically increased the identification of novel parvoviruses in both diseased and healthy individuals. While some of these discoveries have solved etiologic mysteries of well-described diseases in animals, many of the newly discovered parvoviruses appear to cause mild or no disease, or disease associations remain to be established. With the increased use of animal parvoviruses as vectors for gene therapy and oncolytic treatments in humans, it becomes all the more important to understand the diversity, pathogenic potential, and evolution of this diverse family of viruses. In this review, we discuss parvoviruses infecting vertebrate animals, with a special focus on pathogens of veterinary significance and viruses discovered within the last four years.

Investigation of Three Newly Identified Equine Parvoviruses in Blood and Nasal Fluid Samples of Clinically Healthy Horses and Horses with Acute Onset of Respiratory Disease

Simple Summary

The objective of the present study was to determine the molecular frequency of three recently identified parvoviruses (equine parvovirus hepatitis, equine parvovirus CSF and equine copivirus) in blood and respiratory secretions of 667 equids with acute onset of fever and respiratory signs and 87 clinically healthy horses. One hundred and seventeen sick horses tested qPCR-positive for at least one of the three parvoviruses. Ten clinically healthy horses tested qPCR-positive for one of the equine parvoviruses. The frequency of detection of the three equine parvoviruses was similar between sick and clinically healthy horses, suggesting that these newly characterized viruses do not appear to contribute to the clinical picture of equids with respiratory disease. In order to prove the clinical relevance of any of these newly identified equine parvoviruses, experimental challenge studies using pure, clonal inocula will be required.

Abstract

Three newly identified equine parvoviruses (equine parvovirus hepatitis (EqPV-H), equine parvovirus CSF (EqPV-CSF) and equine copivirus (Eqcopivirus)) have recently been discovered in horses with respiratory signs. However, the clinical impact of these three equine parvoviruses has yet to be determined. Nasal fluid samples and blood from 667 equids with acute onset of fever and respiratory signs submitted to a diagnostic laboratory were analyzed for the presence of common equine respiratory pathogens (equine influenza virus, equine herpesvirus-1/-4, equine rhinitis A and B virus, S. equi subspecies equi) as well as EqPV-H, EqPV-CSF and Eqcopivirus by qPCR. An additional 87 clinically healthy horses served as controls. One hundred and seventeen sick horses tested qPCR-positive for at least one of the three parvoviruses. Co-infections with common respiratory pathogens and parvoviruses were seen in 39 sick equids. All 87 clinically healthy horses tested qPCR-negative for all tested common respiratory pathogens and 10 healthy horses tested qPCR-positive for one of the equine parvoviruses. When the frequency of detection for EqPV-H, EqPV-CSF and Eqcopivirus of equids with respiratory signs was compared to that of clinically healthy horses, the difference was not statistically significant (p > 0.05), suggesting that the three recently identified equine parvoviruses do not contribute to the clinical picture of equids with respiratory disease.

First Clinical Case of Equine Parvovirus-Hepatitis-Related Theiler's Disease in Asia

Equine parvovirus-hepatitis (EqPV-H) is a newly identified etiologic agent of Theiler’s disease (TD). We present a case of EqPV-H-related fulminant hepatitis in a 14-year-old thoroughbred mare in Korea. The mare had acute hepatopathy and gastrointestinal symptoms, with abnormal liver-related blood parameters. The horse was born in the USA and imported to Korea in 2017, with no history of administration of equine biological products after entry into Korea. The horse was diagnosed with EqPV-H-associated hepatitis after abdominal ultrasonography, laparotomy, and nested polymerase chain reaction (PCR) and in situ hybridization (ISH) assays. The serum, nasal swab, oral swab, and liver biopsy were positive for EqPV-H according to the PCR assay. Genetic analysis of the partial NS1 gene of EqPV-H showed a unique nucleotide substitution, distinct from that in previously deposited strains. EqPV-H DNA was found not only in hepatocytes but also in bile duct epithelium and Kupffer cells, particularly via ISH. To the best of our knowledge, this is the first case of EqPV-H-associated TD in Asia, providing the first clinical evidence for viral shedding from the mouth and nose, and identification of EqPV-H in the liver. This study contributes to a better understanding of the pathological features of EqPV-H-associated TD.

Equine Parvovirus-Hepatitis Screening in Horses and Donkeys with Histopathologic Liver Abnormalities

There is strong evidence that equine parvovirus-hepatitis (EqPV-H) is associated with the onset of Theiler's disease, an acute hepatic necrosis, in horses. However, the impact of this virus on other hepatopathies remains unknown. The objective of this retrospective study was to evaluate the prevalence and quantify the viral loads of EqPV-H in formalin-fixed, paraffin-embedded equine and donkey livers with various histopathologic abnormalities. The pathologies included cirrhosis, circulatory disorders of the liver, toxic and metabolic hepatic diseases as well as neoplastic and inflammatory diseases (n = 84). Eight normal liver samples were included for comparison as controls. EqPV-H DNA was qualitatively and quantitatively measured by real-time PCR and digital PCR, respectively. The virus was detected in two livers originating from horses diagnosed with abdominal neoplasia and liver metastasis (loads of 5 × 10³ and 9.5 × 10³ genome equivalents per million cells). The amount of viral nucleic acids measured indicates chronic infection or persistence of EqPV-H, which might have been facilitated by the neoplastic disease. In summary, this study did not provide evidence for EqPV-H being involved in hepatopathies other than Theiler's disease.

Clinical Course of Infection and Cross-Species Detection of Equine Parvovirus-Hepatitis

Since its first discovery by Arnold Theiler in 1918, serum hepatitis also known as Theiler’s disease has been reported worldwide, causing idiopathic acute hepatitis and liver failure in horses. Recent studies have suggested a novel parvovirus, named equine parvovirus hepatitis (EqPV-H), to be associated with Theiler’s disease. Despite the severity and potential fatality of EqPV-H infection, little is known about the possibility of developing chronic infections and putative cross-species infection of equine sister species. In the present longitudinal study, we employed qPCR analysis, serology, and biochemical testing as well as pathology examination of liver biopsies and sequence analysis to investigate potential chronic EqPV-H infection in an isolated study cohort of in total 124 horses from Germany over five years (2013–2018). Importantly, our data suggest that EqPV-H viremia can become chronic in infected horses that do not show biochemical and pathological signs of liver disease. Phylogenetic analysis by maximum likelihood model also confirms high sequence similarity and nucleotide conservation of the multidomain nuclear phosphoprotein NS1 sequences from equine serum samples collected between 2013–2018. Moreover, by examining human, zebra, and donkey sera for the presence of EqPV-H DNA and VP1 capsid protein antibodies, we found evidence for cross-species infection in donkey, but not to human and zebra. In conclusion, this study provides proof for the occurrence of persistent EqPV-H infection in asymptomatic horses and cross-species EqPV-H detection in donkeys.

Equine parvovirus-hepatitis is detected in South America, Brazil

The equine parvovirus-hepatitis (EqPV-H), recently identified in association with serum hepatitis in horses (also known as Theiler's disease), has been so far described in horses from North America, Asia and Europe. There is no information regarding its circulation in South America. Our retrospective study (2013-2016) screened by EqPV-H nested-PCR a total of 96 Brazilian horses grouped according to previous status of infection: Known to be positive for one or more horse "hepatitis viruses" (equine hepacivirus, equine pegivirus-EPgV and Theiler's disease-associated virus) and known to be negative. Serum biochemical parameters (aspartate aminotransferase, gamma-glutamyl transferase and glutamate dehydrogenase) were evaluated in EqPV-H positive horses. Molecular characteristics of the isolates were analyzed by DNA sequencing and phylogenetic analysis. EqPV-H DNA was detected in 12.5% (12/96) of horses from 46.6% (7/15) of the farms evaluated. Similar results were obtained between coinfected group (12.3%, 7/57) and non-coinfected group (12.8%, 5/39). Coinfection with EPgV was the most frequent (5/7). Altered serum biochemical parameters suggested a subclinical hepatopathy in some animals (3/12), but the majority presented no clinical or laboratory signs of infection. Nucleotide identity was higher than 94% in comparison with previous isolates. In conclusion, we demonstrated, for the first time in South America, the circulation of EqPV-H. The Brazilian isolates presented a low genetic variability, thus corroborating previous evidence.

Equine parvovirus hepatitis

Equine parvovirus hepatitis (EqPV‐H) was first described in 2018 in a fatal case of Theiler's disease which followed the administration of an equine‐origin biological product. The virus has since been frequently identified in serum and liver tissue of horses affected by Theiler's disease—an acute, severe hepatitis characterised by fulminant hepatic necrosis with a fatal outcome in most cases. EqPV‐H is hepatotropic, appears to be associated with subclinical to severe hepatitis in horses, and is a likely cause of Theiler's disease. Although this disease is most frequently reported following the administration of equine‐origin biological products, it can also occur among in‐contact horses. Horizontal transmission may be iatrogenic, via contaminated equine‐origin biological products such as equine serum, botulism or tetanus antitoxin, and mesenchymal stem cells or by means of the oral route of infection. Other horizontal transmission routes, for example, arthropod vectors, warrant further investigation. A worldwide prevalence of EqPV‐H antibodies and DNA has been reported in asymptomatic horses. EqPV‐H‐positive horses suffering from acute, severe hepatitis have reportedly developed clinical signs including icterus, lethargy, inappetence, and neurological abnormalities and have had increased liver‐associated biochemistry parameters recorded. The most common histopathological abnormalities of the liver have been hepatocellular necrosis, collapse of the lobular architecture, and lymphocytic infiltration. Most horses infected experimentally with EqPV‐H have developed subclinical hepatitis, and close temporal associations between peak viraemia, seroconversion, and the onset of hepatitis have been observed. Based on strong evidence indicating that EqPV‐H causes hepatitis in horses, veterinarians should consider this virus an important differential diagnosis in such cases. Potential risks associated with the administration of equine‐origin biological products must be emphasised.

Circovirus in Blood of a Febrile Horse with Hepatitis

Circoviruses infect vertebrates where they can result in a wide range of disease signs or in asymptomatic infections. Using viral metagenomics we analyzed a pool of five sera from four healthy and one sick horse. Sequences from parvovirus-H, equus anellovirus, and distantly related to mammalian circoviruses were recognized. PCR identified the circovirus reads as originating from a pregnant mare with fever and hepatitis. That horse's serum was also positive by real time PCR for equine parvovirus H and negative for the flavivirus equine hepacivirus. The complete circular genome of equine circovirus 1 strain Charaf (EqCV1-Charaf) was completed using PCR and Sanger sequencing. EqCV1 replicase showed 73-74% identity to those of their closest relatives, pig circoviruses 1/2, and elk circovirus. The closest capsid proteins were from the same ungulate circoviruses with 62-63% identity. The overall nucleotide identity of 72% to its closest relative indicates that EqCV1 is a new species in the Circovirus genus, the first reported in genus Equus. Whether EqCV1 alone or in co-infections can result in disease and its prevalence in different equine populations will require further studies now facilitated using EqCV1's genome sequence.

Active equine parvovirus-hepatitis infection is most frequently detected in Austrian horses of advanced age

BACKGROUND

Equine parvovirus-hepatitis (EqPV-H) research is in its infancy. Information regarding prevalence, geographical distribution, genetic diversity, pathogenesis and risk factors enhances understanding of this potentially fatal infection.

OBJECTIVES

Determining the prevalence of EqPV-H in Austrian equids. Investigating factors increasing probability of infection, liver-associated biochemistry parameters, concurrent equine hepacivirus (EqHV) infection and phylogenetic analysis of Austrian EqPV-H variants.

STUDY DESIGN

Cross-sectional study.

METHODS

Sera from 259 horses and 13 donkeys in Austria were analysed for anti-EqPV-H VP1-specific antibodies by luciferase immunoprecipitation system (LIPS) and EqPV-H DNA by nested polymerase chain reaction (PCR). Associations between infection status, sex and age were described. Glutamate dehydrogenase (GLDH), gamma-glutamyl transferase (GGT), bile acids and albumin concentrations were compared between horses with active infection and PCR-negative horses. PCR targeting partial EqPV-H NS1 was performed and phylogenetic analysis of Austrian EqPV-H variants was conducted. Complete coding sequences (CDS) of four Austrian variants were determined by next-generation sequencing (NGS) and compared with published sequences.

RESULTS

Horses' EqPV-H seroprevalence was 30.1% and DNA prevalence was 8.9%. One horse was co-infected with EqHV. Significantly, higher probability of active EqPV-H infection was identified in 16- to 31-year-old horses, compared with 1- to 8-year-old horses (P = 0.002; OR = 8.19; 95% CI = 1.79 to 37.50) and 9- to 15-year-old horses (P = 0.03; OR = 2.96; 95% CI = 1.08 to 8.17). Liver-associated plasma parameters were not significantly different between horses with active infection and controls. Austrian EqPV-H variants revealed high similarity to sequences worldwide. No evidence of EqPV-H was detected in donkeys.

MAIN LIMITATIONS

Equids' inclusion depended upon owner consent. There was only one sampling point per animal and the sample of donkeys was small.

CONCLUSIONS

EqPV-H antibodies and DNA are frequently detected in Austrian horses, without associated hepatitis in horses with active infection. The risk of active EqPV-H infection increases with increasing age. Phylogenetic evidence supports close relation of EqPV-H variants globally, including Austrian variants.

Discovery of a Novel Simian Pegivirus in Common Marmosets (Callithrix jacchus) with Lymphocytic Enterocolitis

From 2010 to 2015, 73 common marmosets (Callithrix jacchus) housed at the Wisconsin National Primate Research Center (WNPRC) were diagnosed postmortem with lymphocytic enterocolitis. We used unbiased deep-sequencing to screen the blood of deceased enterocolitis-positive marmosets for viruses. In five out of eight common marmosets with lymphocytic enterocolitis, we discovered a novel pegivirus not present in ten matched, clinically normal controls. The novel virus, which we named Southwest bike trail virus (SOBV), is most closely related (68% nucleotide identity) to a strain of simian pegivirus A isolated from a three-striped night monkey (Aotus trivirgatus). We screened 146 living WNPRC common marmosets for SOBV, finding an overall prevalence of 34% (50/146). Over four years, 85 of these 146 animals died or were euthanized. Histological examination revealed 27 SOBV-positive marmosets from this cohort had lymphocytic enterocolitis, compared to 42 SOBV-negative marmosets, indicating no association between SOBV and disease in this cohort (p = 0.0798). We also detected SOBV in two of 33 (6%) clinically normal marmosets screened during transfer from the New England Primate Research Center, suggesting SOBV could be exerting confounding influences on comparisons of common marmoset studies from multiple colonies.

Equine pegiviruses cause persistent infection of bone marrow and are not associated with hepatitis

Pegiviruses frequently cause persistent infection (as defined by >6 months), but unlike most other Flaviviridae members, no apparent clinical disease. Human pegivirus (HPgV, previously GBV-C) is detectable in 1–4% of healthy individuals and another 5–13% are seropositive. Some evidence for infection of bone marrow and spleen exists. Equine pegivirus 1 (EPgV-1) is not linked to disease, whereas another pegivirus, Theiler’s disease-associated virus (TDAV), was identified in an outbreak of acute serum hepatitis (Theiler’s disease) in horses. Although no subsequent reports link TDAV to disease, any association with hepatitis has not been formally examined. Here, we characterized EPgV-1 and TDAV tropism, sequence diversity, persistence and association with liver disease in horses. Among more than 20 tissue types, we consistently detected high viral loads only in serum, bone marrow and spleen, and viral RNA replication was consistently identified in bone marrow. PBMCs and lymph nodes, but not liver, were sporadically positive. To exclude potential effects of co-infecting agents in experimental infections, we constructed full-length consensus cDNA clones; this was enabled by determination of the complete viral genomes, including a novel TDAV 3’ terminus. Clone derived RNA transcripts were used for direct intrasplenic inoculation of healthy horses. This led to productive infection detectable from week 2–3 and persisting beyond the 28 weeks of study. We did not observe any clinical signs of illness or elevation of circulating liver enzymes. The polyprotein consensus sequences did not change, suggesting that both clones were fully functional. To our knowledge, this is the first successful extrahepatic viral RNA launch and the first robust reverse genetics system for a pegivirus. In conclusion, equine pegiviruses are bone marrow tropic, cause persistent infection in horses, and are not associated with hepatitis. Based on these findings, it may be appropriate to rename the group of TDAV and related viruses as EPgV-2.

Transmissible hepatitis in horses (Theiler’s disease) has been known for 100 years without knowledge of causative infectious agents. Recently, two novel equine pegiviruses (EPgV) were discovered. Whereas EPgV-1 was not associated to disease, the other was identified in an outbreak of acute serum hepatitis and therefore named Theiler’s disease-associated virus (TDAV). This finding was surprising since human and monkey pegiviruses typically cause long-term infection without associated clinical disease. Whereas no subsequent reports link TDAV to disease, the original association to hepatitis has not been formally examined. Here, we studied EPgV-1 and TDAV and found that their natural history of infection in horses were remarkably similar. Examination of various tissues identified the bone marrow as the primary site of replication for both viruses with no evidence of replication in the liver. To exclude potential effects of other infectious agents, we developed molecular full-length clones for EPgV-1 and TDAV and were able to initiate infection in horses using derived synthetic viral genetic material. This demonstrated long-term infection, but no association with hepatitis. These findings call into question the connection between TDAV, liver infection, and hepatitis in horses.

Identification of a novel bovine copiparvovirus in pooled fetal bovine serum

A novel parvovirus was identified as a cell culture contaminant by metagenomic analysis. Droplet digital PCR (ddPCR) was used to determine viral loads in the cell culture supernatant and further analysis, by ddPCR and DNA sequencing, demonstrated that fetal bovine serum (FBS) used during cell culture was the source of the parvovirus contamination. The FBS contained ~ 50,000 copies of the novel parvovirus DNA per ml of serum. The viral DNA was resistant to DNAse digestion. Near-full length sequence of the novel parvovirus was determined. Phylogenetic analysis demonstrated that virus belongs to the Copiparvovirus genus, being most closely related to bovine parvovirus 2 (BPV2) with 41% identity with the non-structural protein NS1 and 47% identity with the virus capsid protein of BPV2. A screen of individual and pooled bovine sera identified a closely related variant of the novel virus in a second serum pool. For classification purposes, the novel virus has been designated bovine copiparvovirus species 3 isolate JB9 (bocopivirus 3-JB9).

First report of equine parvovirus-hepatitis-associated Theiler's disease in Europe

BACKGROUND

Equine parvovirus-hepatitis (EqPV-H) has been proposed as the aetiological cause of Theiler's disease, also known as serum hepatitis. EqPV-H-associated Theiler's disease has not been previously reported in Europe.

OBJECTIVES

To determine whether EqPV-H infection was associated with a 2018-2019 outbreak of Theiler's disease in four horses on a studfarm.

STUDY DESIGN

Descriptive case series.

METHODS

The medical records of four horses from the same farm diagnosed with fatal Theiler's disease were examined retrospectively. Information collected included a clinical history, physical examination findings, tetanus antitoxin exposure, serum biochemistry and necropsy reports. Liver tissue from all four horses was tested for EqPV-H using PCR and in situ hybridisation (ISH) assays.

RESULTS

Three of the horses had a history of recent (7-11 weeks) tetanus antitoxin administration. Liver tissue from all four horses tested positive for EqPV-H with PCR. In situ hybridisation revealed a widespread distribution of viral nucleic acid in hepatocytes in one case, and a more sporadic distribution in the remaining three cases.

MAIN LIMITATIONS

Case controls were not available from the farm in question given the retrospective nature of analysis.

CONCLUSIONS

This case series documents the first reported EqPV-H-associated Theiler's disease in Europe and the first use of ISH to visualise the viral nucleic acid in liver tissues of horses with Theiler's disease.

Tropism, pathology, and transmission of equine parvovirus-hepatitis

Equine parvovirus-hepatitis (EqPV-H) has recently been associated with cases of Theiler's disease, a form of fulminant hepatic necrosis in horses. To assess whether EqPV-H is the cause of Theiler's disease, we first demonstrated hepatotropism by PCR on tissues from acutely infected horses. We then experimentally inoculated horses with EqPV-H and 8 of 10 horses developed hepatitis. One horse showed clinical signs of liver failure. The onset of hepatitis was temporally associated with seroconversion and a decline in viremia. Liver histology and in situ hybridization showed lymphocytic infiltrates and necrotic EqPV-H-infected hepatocytes. We next investigated potential modes of transmission. Iatrogenic transmission via allogeneic stem cell therapy for orthopedic injuries was previously suggested in a case series of Theiler's disease, and was demonstrated here for the first time. Vertical transmission and mechanical vectoring by horse fly bites could not be demonstrated in this study, potentially due to limited sample size. We found EqPV-H shedding in oral and nasal secretions, and in feces. Importantly, we could demonstrate EqPV-H transmission via oral inoculation with viremic serum. Together, our findings provide additional information that EqPV-H is the likely cause of Theiler's disease and that transmission of EqPV-H occurs via both iatrogenic and natural routes.

Equine Parvovirus-Hepatitis in China: Characterization of Its Genetic Diversity and Evidence for Natural Recombination Events Between the Chinese and American Strains

Equine parvovirus-hepatitis (EqPV-H) was first reported in a horse that died of equine serum hepatitis in the USA in 2018, and was determined having a strong association with equine serum hepatitis in the following studies. As a newly discovered virus, the genomic sequences of only seven EqPV-H strains have been reported. Considering this, an epidemiological study was performed to investigate the prevalence of EqPV-H in equines in Guangdong Province in China, and obtain genomic sequences of the field prevalent EqPV-H strains. The detection rate of EqPV-H was finally determined to be 8.33% (95% CI: 2.8-18.4%), and EqPV-H's coinfection with equine hepacivirus and equine pegivirus was also determined. Then, the genomes of the Chinese field EqPV-H strains were obtained by PCR, sequencing, and assembly. Through bootscanning analysis, Simplot analysis, and phylogenetic analysis, strong evidence for natural recombination events were found in two Chinese field EqPV-H strains. The natural recombination events occurred between the Chinese and American strains, and were determined within VP protein. Finally, the genetic distance of EqPV-H strains was investigated. Nucleotide identities of 97.1-99.9% and 95.2-100% were found for NS and VP between EqPV-H strains, respectively. Together with other molecular evidence obtained in the present study, the genetic diversity of EqPV-H was determined. Taken together, the results of the present study expand our knowledge on the epidemiological characteristics, genetic variability, and evolution of EqPV-H.

The association of Equine Parvovirus-Hepatitis (EqPV-H) with cases of non-biologic-associated Theiler's disease on a farm in Ontario, Canada

Theiler's disease was confirmed within a group horses located on a farm in southwestern Ontario during the summer and autumn of 2005. Five sudden deaths occurred between 3 July and 21 August, 2005, none of which were necropsied, however two of the horses showed clinical signs compatible with hepatic encephalopathy prior to death. No horse on the farm had received a biologic product of equine blood origin in the preceding six months. The only biologics used on the property were the administration of killed vaccines for rabies, tetanus and West Nile Virus to all horses 30 days prior to the onset of the first sudden death. Between 22 August, 2005 and 21 October, 2005, a further four horses died suddenly or were euthanized with all having a confirmed histopathologic diagnosis of acute hepatic necrosis. Serum was collected from all horses on the farm on 30 September, 2005 and this was repeated on 29 October, 2005. Equine parvovirus-hepatitis (EqPV-H) DNA was detected by quantitative-PCR in the serum of 61.8% (34/55) of the horses on the farm on either one or both sampling dates with viral loads ranging from <3.75 × 10³ copies/mL to 3.64 × 10⁷ copies/mL. EqPV-H DNA was present in serum samples of three horses with a confirmed diagnosis of Theiler's disease, five horses with subclinical liver disease, and in clinically normal in-contact horses. Subsequent phylogenetic analysis based on partial NS1 of EqPV-H revealed not only high similarity on nucleotide level within the sequenced samples but also within other previously published sequences.

Characterization of Equine Parvovirus in Thoroughbred Breeding Horses from Germany

An equine parvovirus-hepatitis (EqPV-H) has been recently identified in association with equine serum hepatitis, also known as Theiler's disease. The disease was first described by Arnold Theiler in 1918 and is often observed with parenteral use of blood products in equines. However, natural ways of viral circulation and potential risk factors for transmission still remain unknown. In this study, we investigated the occurrence of EqPV-H infections in Thoroughbred horses in northern and western Germany and aimed to identify potential risk factors associated with viral infections. A total of 392 Thoroughbreds broodmares and stallions were evaluated cross-sectionally for the presence of anti-EqPV-H antibodies and EqPV-H DNA using a luciferase immunoprecipitation assay (LIPS) and a quantitative PCR, respectively. In addition, data regarding age, stud farm, breeding history, and international transportation history of each horse were collected and analysed. An occurrence of 7% EqPV-H DNA positive and 35% seropositive horses was observed in this study cohort. The systematic analysis of risk factors revealed that age, especially in the group of 11-15-year-old horses, and breeding history were potential risk factors that can influence the rate of EqPV-H infections. Subsequent phylogenetic analysis showed a high similarity on nucleotide level within the sequenced Thoroughbred samples. In conclusion, this study demonstrates circulating EqPV-H infections in Thoroughbred horses from central Europe and revealed age and breeding history as risk factors for EqPV-H infections.

Multidecade Mortality and a Homolog of Hepatitis C Virus in Bald Eagles (Haliaeetus leucocephalus), the National Bird of the USA

The bald eagle (Haliaeetus leucocephalus) once experienced near-extinction but has since rebounded. For decades, bald eagles near the Wisconsin River, USA, have experienced a lethal syndrome with characteristic clinical and pathological features but unknown etiology. Here, we describe a novel hepacivirus-like virus (Flaviviridae: Hepacivirus) identified during an investigation of Wisconsin River eagle syndrome (WRES). Bald eagle hepacivirus (BeHV) belongs to a divergent clade of avian viruses that share features with members of the genera Hepacivirus and Pegivirus. BeHV infected 31.9% of eagles spanning 4,254 km of the coterminous USA, with negative strand viral RNA demonstrating active replication in liver tissues. Eagles from Wisconsin were approximately 10-fold more likely to be infected than eagles from elsewhere. Eagle mitochondrial DNA sequences were homogeneous and geographically unstructured, likely reflecting a recent population bottleneck, whereas BeHV envelope gene sequences showed strong population genetic substructure and isolation by distance, suggesting localized transmission. Cophylogenetic analyses showed no congruity between eagles and their viruses, supporting horizontal rather than vertical transmission. These results expand our knowledge of the Flaviviridae, reveal a striking pattern of decoupled host/virus coevolution on a continental scale, and highlight knowledge gaps about health and conservation in even the most iconic of wildlife species.

Viruses in Horses with Neurologic and Respiratory Diseases

Metagenomics was used to identify viral sequences in the plasma and CSF (cerobrospinal fluid) of 13 horses with unexplained neurological signs and in the plasma and respiratory swabs of 14 horses with unexplained respiratory signs. Equine hepacivirus and two copiparvoviruses (horse parvovirus-CSF and a novel parvovirus) were detected in plasma from neurological cases. Plasma from horses with respiratory signs contained the same two copiparvoviruses plus equine pegivirus D and respiratory swabs contained equine herpes virus 2 and 5. Based on genetic distances the novel copiparvovirus qualified as a member of a new parvovirus species we named Eqcopivirus. These samples plus another 41 plasma samples from healthy horses were tested by real-time PCRs for multiple equine parvoviruses and hepacivirus. Over half the samples tested were positive for one to three viruses with eqcopivirus DNA detected in 20.5%, equine hepacivirus RNA and equine parvovirus-H DNA in 16% each, and horse parvovirus-CSF DNA in 12% of horses. Comparing viral prevalence in plasma none of the now three genetically characterized equine parvoviruses (all in the copiparvovirus genus) was significantly associated with neurological and respiratory signs in this limited sampling.

Equine Parvovirus-Hepatitis Frequently Detectable in Commercial Equine Serum Pools

An equine parvovirus-hepatitis (EqPV-H) has been recently identified in association with equine serum hepatitis, also known as Theiler’s disease. This disease was first described by Arnold Theiler in 1918 and is often observed after applications with blood products in equines. So far, the virus has only been described in the USA and China. In this study, we evaluated the presence of EqPV-H in several commercial serum samples to assess the potential risk of virus transmission by equine serum-based products for medical and research applications. In 11 out of 18 commercial serum samples, EqPV-H DNA was detectable with a viral load up to 10⁵ copies/mL. The same serum batches as well as three additional samples were also positive for antibodies against the EqPV-H VP1 protein. The countries of origin with detectable viral genomes included the USA, Canada, New Zealand, Italy, and Germany, suggesting a worldwide distribution of EqPV-H. Phylogenetic analysis of the EqPV-H NS1 sequence in commercial serum samples revealed high similarities in viral sequences from different geographical areas. As horse sera are commonly used for the production of anti-sera, which are included in human and veterinary medical products, these results implicate the requirement for diagnostic tests to prevent EqPV-H transmission.

What Do We Know About Hepatitis Viruses in Horses?

Theiler disease (serum hepatitis or idiopathic acute hepatic necrosis) has long been suspected to have a viral etiology. Four viruses have been described in association with hepatitis in horses. Further investigation suggests equine pegivirus and Theiler disease-associated virus (a second pegivirus) are neither hepatotropic nor pathogenic. Nonprimate hepacivirus (NPHV) causes subclinical disease in experimental models and has been associated with hepatitis in some clinical cases. Equine parvovirus-hepatitis (EqPV-H) experimentally causes subclinical-to-clinical liver disease and is found in the vast majority of Theiler disease cases. EqPV-H is likely of clinical significance, whereas the significance of NPHV is unknown.

Viral testing of 10 cases of Theiler's disease and 37 in-contact horses in the absence of equine biologic product administration: A prospective study (2014-2018)

Background

A novel equine parvovirus (EqPV‐H) was recently discovered in the equine liver with Theiler's disease.

Objectives

To determine the prevalence of EqPV‐H infection in naturally occurring Theiler's disease cases and in‐contact horses in the absence of historical equine biologic product administration.

Animals

Ten cases of Theiler's disease from 6 separate properties were included in the study, based on the criteria of acute onset of clinical signs of liver failure with laboratory or histopathologic findings characteristic of Theiler's disease and no history of receiving an equine biologic product within the preceding 4 months. In addition, 37 in‐contact horses from 4 of the 6 properties were screened for EqPV‐H infection and hepatitis.

Methods

In prospective case series, cases were diagnosed with Theiler's disease by the attending veterinarian and were tested for EqPV‐H by PCR of liver or serum. In‐contact horses were assessed via serum chemistry and PCR at the attending veterinarian's discretion. Hepatitis was defined as serum gamma‐glutamyltransferase activity above reference interval. The association of EqPV‐H with hepatitis was determined by Fisher's exact test.

Results

Nine of 10 (90%) Theiler's disease cases and 54% of tested in‐contact horses were EqPV‐H positive. Hepatitis was significantly associated with EqPV‐H infection (P = .036).

Conclusions and Clinical Importance

Although further study is required to identify EqPV‐H as the causative agent of Theiler's disease, EqPV‐H appears strongly associated with cases of fatal Theiler's disease and subclinical hepatitis in horses in contact with those cases. The prevalence of EqPV‐H infection on affected properties can be high.