Researchers Working to Address Risk of AHS Spread

Researchers Working to Address Risk of AHS Spread

Climate change and international horse movement could both contribute to the risk of AHS spreading outside its traditional area.

Photo: Manuel Rodriguez

As the climate changes and horses travel internationally more frequently, the deadly disease African horse sickness (AHS) might soon seem less exotic, researchers from around the world say.

Faced with the imminent threat of the “equine plague,” as it’s called in French, international scientists from across the globe convened at the World Animal Health Organization (OIE) headquarters in Paris earlier this year to address this potential threat and find solutions.

“We hope to encourage, develop, and enrich the collaboration among countries dealing with a disease that would have dramatic consequences on the equine industry if we are insufficiently prepared for its arrival,” said Jean-Yves Gauchot, DVM, president of the French surveillance center for equine pathologies (RESPE) in Caen. The RESPE organized this first international conference to address “AHS: A Danger at our Doorstep.”

African horse sickness affects primarily equids, but also camels and dogs. It’s caused by the AHS virus that biting midges transmit from host to host. While the disease is most deadly to horses (up to 90% mortality rate in unvaccinated animals) and somewhat less deadly for donkeys and mules, it has no clinical effect on zebras, said Alan Guthrie, BVSc, MedVet, PhD, director of the University of Pretoria’s Equine Research Centre, in South Africa. But because midges can still transmit the virus to these striped equids, “the zebra population is therefore a permanent reservoir for the AHS virus,” he said.

Equids, including zebras, traveling out of Africa could potentially carry the virus around the world if not tested and quarantined before being transported to their final destination. For example, affected zebras shipped to Europe were the source of an outbreak in Spain in 1987, which later extended to Portugal and Morocco and caused great losses in horses, said José-Manuel Sanchez-Vizcaino, DVM, PhD, professor at Complutense University, in Madrid, Spain. In that case, the zebras were transported during the disease’s active season (warm months), and they were not quarantined under vector protection (insect-proof housing).

Today, climate change is creating conducive conditions for this disease’s vectors, thereby increasing its risk of spreading further than it has in the past, said Guthrie. African midges can now travel farther north, bringing the disease with them. And European outbreaks can be more difficult to control if the winters aren’t cold enough to stop midge activity for a long enough period to “winter out” the disease. This is a phenomenon that Europe is already experiencing with bluetongue, the equivalent of AHS in sheep, spread by the same insect vectors.

But Europe isn’t the only continent at risk. Even South America—and, subsequently, North America, could become exposed to the disease, said Sanchez-Vizcaino. “The polo horse trade out of South Africa into Argentina is a significant source of risk,” he explained. “If the disease gets into Argentina, it can travel north all the way up into Mexico and the U.S. and even Canada.

“Due to the high number of horse movements in the equine industry, quarantine is the best tool we have to protect ourselves from AHS,” he continued. “Special attention must be made between movements from AHS-risk areas to AHS-free areas.”

There is no cure, or even effective treatment, for AHS, Guthrie said. The only real way to manage the disease is through prevention via vector-protected quarantines and vaccines.

Sanchez-Vizcaino said the currently available vaccines are based on live attenuated viruses, and horses can actually become infectious from the vaccine itself. Furthermore, midges can spread the virus contained in the vaccine to other unvaccinated horses.

“This fact could create great problems to the control of AHS in non-endemic areas,” he said.

“In this time of globalization, maintaining a high level of vigilance concerning exotic diseases that can cross borders and preparing for the ability to react to those diseases are critical for limiting the potential impact of any introduction or emergence,” added Monique Eloit, DVM, director general of the World Organization for Animal Health (OIE).

The OIE oversees transparency of AHS cases in its 180 member countries and grants “AHS-free” status to countries that can prove the absence of AHS for at least two years. It is also promoting the application of OIE standards by governments worldwide for safe horse trade while preventing and recognizing the disease and managing possible outbreaks.

The OIE is also contributing to advanced research into AHS diagnosis and into the development of new-generation vaccines against AHS, Eloit said.

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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