African Horse Sickness Plague

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South Africa is experiencing an outbreak of African horse sickness, a viral disease that attacks the heart, lungs or both and is fatal to 75 to 90% of horses infected, 50% of mules and about 10% of donkeys. As of the end of March, nearly 270 equine cases had been recorded and 155 deaths.

African horse sickness or ”horse plague,” has been recognized in horses in southern Africa since at least the 1700s. Periodic spread has been documented as far north as Portugal.

It’s transmitted from horse to horse by the bites of the Culicoides species of biting midges, aka ”no-see-ums,” the same tiny fly responsible for sweet-itch allergy and summer-midline dermatitis in susceptible horses in this country and Europe. The virus can also be spread by other biting flies and ticks.

The most consistent symptom of AHS is the development of swelling in the supraorbital fossa, the normally hollow area above the eyes. Fever with edema of the head, neck and chest may occur in some forms. Extreme difficulty breathing and death within a few days develop in the fatal cases.

Bottom Line: There is no evidence that the current outbreak of AHS poses a threat to horses in North America. Current USDA import requirements call for a 60-day quarantine for horses coming from areas where AHS is known to be present. This should be more than adequate to pick up horses infected with the virus that could spread it via insect bites.

Import restrictions don’t apply to hitchhiking insects, of course. In the case of AHS, animals that may harbor this virus without harm, and therefore keep it in circulation, are currently unknown. As the world shrinks, the possibility for diseases previously limited to one area of the world to spreading to others grows.

You can help guard against the establishment of foreign equine diseases here by making sure that any horse with unusual symptoms or serious illness of unclear cause associated with fever is reported by your vet to the state veterinarian.