Are We Prepared for African Horse Sickness?

African horse sickness is a fatal viral disease spread by Culicoides midges—the same tiny, blood-sucking insects that cause sweet itch—that can affect horses, mules, and donkeys.

Photo: Courtesy Dr. Matthew Robin

Ebola virus made international headlines in 2014 as it spread throughout West Africa. People around the world became hungry for news and other resources to help educate themselves about this life-threatening infection.

But equestrians might want to learn about another African virus—one that's killed countless horses on that continent and has not yet entered the United States or the United Kingdom, but is knocking on the door and, theoretically, could arrive at any time: African horse sickness (AHS).

At the 2014 British Equine Veterinary Association Congress, held Sept. 10-13 in Birmingham, U.K., Matthew Robin, BVSc, BSc, CertAVP(EM), MRCVS, described the risk of an AHS outbreak in Britain and steps to take should an outbreak occur. Robin is the Horserace Betting Levy Board-sponsored resident in equine medicine and infectious diseases at the University of Liverpool's Philip Leverhulme Equine Hospital, in Wirral, U.K.

African horse sickness is a fatal viral disease spread by Culicoides midges— the same tiny, blood-sucking insects that cause sweet itch—that can affect horses, mules, and donkeys, as well as dogs and camels. The disease, endemic in sub-Saharan Africa, has mortality rates as high as 95% in naive populations. A vaccine is available in South Africa, but no effective treatment methods exist for infected horses. For survivors, recovery is slow.


"A U.K. outbreak would have devastating effects on animal welfare and major economic impacts on the equine industry," he said.

What's the Risk?

"There have long been concerns that climate change and globalization—particularly the transportation of animals and animal products—could lead to an increased occurrence of exotic or novel vector-borne diseases within northern Europe," Robin said.

And, while the U.K. has historically been considered at low-risk of seeing an AHS outbreak—mainly due to the fact that the causative species of Culicoides midges aren't prevalent there—a 2007 outbreak of bluetongue virus (which mainly affects sheep and cattle) in that country made some researchers rethink their previous conclusion, he said.

"Bluetongue virus is closely related to AHS virus and shares the same vector species of midges where both diseases are endemic," Robin explained. "Before 2006, bluetongue never occurred in northern Europe, where the traditional vector species of midge are not present; however, it is now known that during the outbreak in the U.K., indigenous midge species (particularly, Obsoletus and Pulicaris species group midges) were able to act as vectors."

Theoretically, the same thing could occur with AHS.

Another concern is climate change, he added: "Climate change may well affect both the distribution of different midge species and their inherent ability to transmit viruses. Our preparedness for an outbreak of AHS is therefore dependent on prevention of viral importation—currently extremely unlikely via legal equid movement—and knowledge of the Culiciodes epidemiology in the U.K., particularly with regard to equine properties."

In that vein, Robin said that study results have shown Obsoletus and Pulicaris group midges comprise 93.5-97% of the midges found on all farms in the U.K. and 99% of the midges found on horse properties.

"Some of these midges were also shown to contain equine DNA, proving a direct vector-host interaction," he said. "It therefore seems possible that an AHS outbreak could occur in the U.K., if the virus were imported."

Managing an Outbreak

So what would happen if there was an AHS outbreak in the U.K.?

Robin explained that the British Department for Environment, Food, and Rural Affairs (DEFRA) has issued a publication outlining the government's AHS control objectives. The regulations outline who must be notified if a horse in England is suspected of having AHS, steps to take once a horse is suspected or confirmed as having AHS, area AHS controls, and AHS vaccinations. The regulations also cover AHS guidelines for surveillance and management in equine slaughterhouses and in feral or wild horses.

He also noted several steps owners can take to reduce their horses' exposure to midges that could potentially carry AHS in the event of an outbreak:

  • "While moving horses to areas without midges would be effective for preventing AHS virus transmission, it is often highly impractical and potentially inappropriate during a disease outbreak," he said;
  • Experience from South Africa indicates that stabling horses overnight and applying mesh or screens over doors, window, and other openings is a useful and practical way to keep midges from contacting horses;
  • Similarly, fly sheets with neck covers provide a barrier between horses and midges; and
  • "The efficacy of topical fly control products is essentially unknown and, at this time, no products are licensed to act against Culicoides midges," Robin said. Nonetheless, DEFRA says owners could use the insecticide deltamethrin under veterinary supervision in some cases, "although there is no specific evidence to support its use in horses," he said.

Take-Home Message

While an AHS outbreak in the U.K. could be a long way off, it could also be closer than we think. Taking steps to prepare ahead of time could help reduce the impact of such an event and keep as many horses as possible healthy throughout an outbreak.

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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