Schmallenberg Virus

A recently discovered virus known to infect ruminants in parts of Europe might infect horses, as well: Researchers have just identified antibodies to the Schmallenberg virus, transmitted by flying insects, in 10 Iranian horses.

They are the first horses worldwide to test positive for these antibodies, the scientists said.

In screening for antibodies in cattle, sheep, and goats, as well as in horses, the researchers discovered—unexpectedly—that members of the equine species tested positive along with the other species, said Mehdi Rasekh, DVM, DVSc, an assistant professor of large animal internal medicine in at the University of Zabol Faculty of Veterinary Medicine, in Iran.

“The results surprised us because the positive response was expected in ruminants, but detecting antibodies against Schmallenberg virus in horses was a new finding in the world,” Rasekh said.

Scientists discovered the Schmallenberg virus in 2011 in Germany and The Netherlands, where it infected cattle, sheep, and goats, he said. Those infections generally led to fever, fetal malformations, and abortion.

Like African horse sickness (AHS) and bluetongue virus, Schmallenberg virus is transmitted by biting midges. With climate change and greater human and animal movement, these tiny winged insects are crossing borders and bringing with them an increased disease risk.

Concerned about the spread of midge-borne diseases into neighboring Turkey, Rasekh and his fellow researchers conducted a serological survey of at-risk species in Iran. They conducted blood tests on a random population of three species of ruminants as well as on 200 randomly selected horses.

They weren’t surprised to find positive results in the cattle, sheep, and goats, given Turkey’s close proximity with its seropositive population, Rasekh said. However, as many as 5% of the tested horses also had positive results.

“Of course, this means new challenges for the equine industry,” he said.

None of the horses showed clinical signs, however. It’s possible that the disease had already run its course by the time the horses were tested, and the antibodies were still present in the system, Rasekh explained. It’s also possible that horses just don’t show clinical disease despite infection.

There’s also a possibility that the ELISA test is giving false positives, he added. “We cannot completely rely on serologic tests to confirm the disease in horses,” he said. “More reliable tests (like a PCR test) are needed to show the virus or its residues, like the virus genome, to confirm the disease in horses.”

The study, “Detection of Schmallenberg virus antibody in equine population of Northern and Northeast of Iran,” was published in Veterinary World