“We found 35% of horses positive for antibodies, meaning that they had contact with the virus at some point in the past,” said Toni Luise Meister, PhD, of the Department of Molecular and Medical Virology in the Faculty of Medicine at Ruhr-University Bochum, in Germany.
“Furthermore, 7% of the horses had virus genetic material found in their serum,” she said. “This indicates that those horses were infected with the virus at the time of sampling.”
DNA testing revealed that these infections were no longer “acute,” meaning the horses were hosting a virus but already had antibodies against it.
EqPV-H passes from one horse to another through blood contact, which can happen if a needle is used on more than one horse, said Eike Steinmann, PhD, also of the Faculty of Medicine’s virology department at Ruhr-University Bochum.
It can also be transmitted through equine biological products—health care products based on equine serum from donor horses. These products include tetanus antitoxin, botulinum antitoxin, Streptococcus equi antiserum, and equine plasma, said Amit Kapoor, PhD, of Ohio State University and the Center for Vaccines and Immunity in Columbus, Ohio.
Natural spread also seems to occur, as some cases involve horses that haven’t been exposed to equine biological products, says Joy Tomlinson, DVM, Dipl. ACVIM, research associate at the Cornell University College of Veterinary Medicine, in Ithaca, New York. In general, viruses might spread through insect vectors, inhalation, or ingestion, for example. However, scientists have yet to determine which routes transmit EqPV-H.
European Rates Slightly Lower Than Those in U.S. and China
The latest study, involving analyses of samples from 392 Thoroughbred broodmares and stallions across northern and western Germany, was the first investigation of EqPV-H prevalence in Europe, says Meister. Since the virus’s discovery in early 2018, its prevalence has only been tested in two other regions worldwide. American scientists noted a 13% exposure rate in U.S. horses, and Chinese scientists found a 12% prevalence in their racehorses. These rates are somewhat higher than the 7% found in the German equine population, Meister said.
Meister, Steinmann, and their fellow researchers selected this group of horses because they are already in close study for other research projects, she said.
Their data reveal a “frequent occurrence” of EqPV-H DNA in their demographic population, which suggests that infections are circulating, that there are endemic herds, or that there is persistent shedding of viruses, said Meister.
Risks: Age and Breeding
Increased age and breeding experience made study horses more likely to test positive, said Steinmann. Surprisingly to the researchers, however, increased travel times and transport to other countries didn’t affect their exposure rates, contrary to that for other common equine viruses, such as equine herpesvirus.
“Many facts about the virus and infection are still unknown,” Steinmann said. “It is therefore likely that the infection is still underdiagnosed.”
Theiler’s disease was first identified in 1918 when horses fell ill with hepatitis in South Africa after receiving vaccines against African horse sickness. However, the agent responsible for the disease was not identified with certainty until a century later. Also known as equine serum hepatitis, Theiler’s disease can cause liver failure in horses. With few treatment options available, it is frequently fatal.
“Our results show that infection with the virus, which can result in fatal serum hepatitis (according to other reports), goes unnoticed in many cases, and that the virus is widely spread,” said Jessika M. V. Cavalleri, PhD, of the Department for Companion Animals and Horses at University of Veterinary Medicine Vienna, Austria. “Thus, it makes sense to test for EqPV-H in cases of liver disease.”
Testing is now available to owners within the Department of Molecular and Medical Virology at Ruhr-University Bochum, via tissue or blood samples.