insect-borne horse diseases

Central Spain, 1987. Dozens of horses fall ill and die. Then it’s hundreds. Before it’s over, an exotic disease will have wiped out 1,400 Spanish equids. The cause? African horse sickness (AHS), which hitched a ride with a herd of zebras imported into a zoo. Investigators determined a key element in the disease’s spread was a simple one: lack of awareness. Owners and veterinarians just didn’t know what to look for or recognize when they saw it.

Nearly 30 years later, researchers in the U.K. want to make sure their country won’t repeat that mistake. And, with the changing climate and the increase in global movement (of horses, animals, people, and goods), the transmission of “exotic” insect-borne horse diseases such as AHS, West Nile virus (WNV), and various encephalitic diseases, is more likely than ever. The time to prepare for foreign arboviruses—viruses spread through biting bugs—is now, said Debra Archer, BVMS, PhD, CertES (soft tissue), Dipl. ECVS, FHEA, FRCVS, of the University of Liverpool’s School of Veterinary Science, in the U.K.

“We had an uncharacteristically long and warm summer (last) year, and that’s a reminder that the climate could change in such a way as to favor the spread of diseases that our horse population has never experienced before,” she said. “It’s critical that owners—and especially veterinarians—be able to recognize signs and risks and act accordingly.”

But can owners recognize signs of foreign disease or the bugs that carry them? Archer and colleagues surveyed British horse owners to find out.

In an online survey, they asked owners to identify flying, biting insect species and indicate if they know whether any are present at their farms, Archer said. They also evaluated owners’ knowledge of the kinds of diseases those bugs could transmit to horses and their clinical signs. Finally, the researchers asked respondents about their horses’ vaccination statuses and the methods they use to repel insects.

The nearly 500 participants had “poor awareness” of arboviruses affecting horses, Archer said. While 70% could recognize a midge from a photo, only 31% of those people knew midges could transmit diseases (including AHS) to horses. Meanwhile, 65% of respondents recognized a photo of a mosquito, but only 36% of them understood that mosquitoes could transmit equine diseases. And only 7% and 16% of respondents could name a disease transmitted by midges or mosquitoes, respectively, to horses.

Just 13% could identify a clinical sign of AHS, and only 3% of the respondents completing this part of the survey believed “death or collapse” could occur with AHS. In reality, AHS can kill 70-95% of infected horses.

“We found that the awareness level was particularly low among U.K. horse owners,” Archer said. “While this might seem concerning, it’s not really a surprise. British horse owners just don’t have to deal with as many exotic diseases, at least not at the moment.”

That could certainly change with climate shifts, however. “Most of our summers wouldn’t necessarily have climactic issues that would support the transmission of an arbovirus,” she said. “But this is something that will become a concern with climate change, and our climate is changing, and we are going to have warmer summers. As far as horses go, we need to be aware that there might be potential for a disease to appear.”

The goal isn’t to put U.K. owners “on the alert” or cause them to worry, Archer added. Rather, it’s important to recognize the starting point for education programs. By working through veterinarians, instructors, pony clubs, equestrian media sources, and websites, scientists can begin to prepare owners for the possible arrival of exotic arboviruses, she said.

They also hope to educate veterinarians, Archer added. “Many of the U.K. veterinarians aren’t able to recognize signs of the disease or adequately mitigate risks, such as through insect control,” she said. “But veterinarians are key because they see a lot of horses across a geographic region and can recognize trends in disease patterns. Their ability to pick up early signs can be critical in disease management.”

The study, “Survey of UK horse owners’ knowledge of equine arboviruses and disease vectors,” was published in the Veterinary Record.