Chronic infections with equine parvovirus-hepatitis (EqPV-H) lasting up to five years in horses without severe clinical signs of liver disease have been identified by researchers.
The study team also found evidence that the recently discovered virus can infect donkeys, but not humans or zebras.
Researchers, writing in the journal Viruses, set out to learn more about the clinical course of infection and investigate cross-species detection of EqPV-H.
Serum hepatitis, also known as Theiler’s disease, is the most common cause of acute and potentially life-threatening viral hepatitis in horses. It was first described by Arnold Theiler in 1918, who observed acute liver atrophy and widespread liver necrosis after the administration of a combination of live virus and convalescent equine antiserum in horses from South Africa.
Since then, outbreaks have been described worldwide in conjunction with a vast variety of equine-derived blood products including tetanus antitoxin, botulinum antitoxin, antiserum against Streptococcus equi, as well as pregnant mare’s serum, and equine plasma.
Incidence rates of severe or sudden hepatitis in horses receiving an equine-derived product have been reported to vary between 1.4% and 18%.
In the past, three flaviviruses, including equine hepacivirus, Pegivirus D, and Pegivirus E have been suggested to be associated with Theiler’s disease. However, only equine hepacivirus has displayed signs of exerting any specific effects on the liver in horses.
Researchers, in a paper published in 2018, described a novel parvovirus designated as equine parvovirus-hepatitis (EqPVH) in the serum and liver of a horse that died in Nebraska 65 days after treatment with equine-origin tetanus antitoxin. Subsequent experiments confirmed EqPV-H as a cause of acute hepatitis and liver failure – that is, Theiler’s disease.
Since then, a high prevalence of EqPV-H genomes has been identified in commercially available horse serum samples from the United States, Canada, New Zealand, Italy, and Germany, indicating a worldwide distribution of EqPV-H.
Incidences of EqPV-H infections in horses without exposure to biological equine serum products have also been described. In a study reported in 2019, EqPV-H DNA was present in 9 out of 10 cases of Theiler’s disease that did not receive biological equine serum products.
Birthe Reinecke and her fellow researchers noted that, despite the severity and potential fatality of EqPV-H infection, little is known about the possibility of developing chronic infections and possible cross-species infection of equine sister species.
The study team employed molecular-based techniques, serology, and biochemical testing, as well as microscopic examination of liver biopsies and sequence analysis, to investigate potential chronic EqPV-H infection in an isolated study group of 124 horses from Germany over five years.
They also tested serum samples from humans, zebras, and donkeys for the presence of anti-EqPVH antibodies and DNA.
The 318 human serum samples included 147 from humans without horse contact and 171 from individuals with occupational horse contact. A total of 494 donkey serum samples from Germany, Italy and Bulgaria were donated by volunteers and collected from across Europe.
Archived samples from 65 Burchell’s zebra and 231 Cape mountain zebra sera, collected between 2009 and 2017 across South Africa, were acquired from a biobank.
Overall, most of the horses used in the study were negative for EqPV-H DNA and antibodies. However, some horses identified with EqPV-H infection exhibited prolonged viremia – that is, the presence of the virus in the blood.
“We identified chronic EqPV-H infections lasting up to five years in horses without severe clinical signs of hepatic disease,” they said.
Horses that had no detectable EqPV-H-DNA in their serum in 2018 after being DNA positive for years hint at a possible clearance of infection, they said.
The findings indicate that EqPV-H viremia can become chronic in infected horses that do not show biochemical and pathological signs of liver disease.
They found evidence of the virus in the blood of about 1% of the donkeys tested (5 of the 494 animals), which is comparably low to serum prevalence found in horses.
“Additionally, we identified two different virus strains among four donkeys from Bulgaria. Further virological and serological surveys are needed to decipher the worldwide geographical distribution of EqPV-H infection in donkeys and possible transmission routes and mechanisms of cross-species transmission need further investigation.
“In addition, we have not examined levels of liver enzymes and the pathology of EqPV-H DNA positive donkeys in this study; hence, further research is needed to investigate putative signs of hepatitis in viremic donkeys.”
They found no evidence of cross-species infection in the samples taken from humans and zebras.
The study team said their work provides proof for the occurrence of persistent EqPV-H infection in symptom-free horses, and cross-species EqPV-H detection in donkeys.
The study team comprised Reinecke, Mara Klöhn, Yannick Brüggemann, Volker Kinast, Daniel Todt, Alexander Stang, Marcha Badenhorst, Katja Koeppel, Alan Guthrie, Ursula Groner, Christina Puff, Madeleine de le Roi, Wolfgang Baumgärtner, Jessika-M. V. Cavalleri and Eike Steinmann, affiliated with a range of German and South African institutions.
Reinecke, B.; Klöhn, M.; Brüggemann, Y.; Kinast, V.; Todt, D.; Stang, A.; Badenhorst, M.; Koeppel, K.; Guthrie, A.; Groner, U.; Puff, C.; de le Roi, M.; Baumgärtner, W.; Cavalleri, J.-M.V.; Steinmann, E. Clinical Course of Infection and Cross-Species Detection of Equine Parvovirus-Hepatitis. Viruses 2021, 13, 1454. https://doi.org/10.3390/v13081454