Equine Science Update
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African Horse Sickness - why worry?
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“Nothing is more likely to disrupt racing and breeding in the UK in the next few years than infectious diseases” warned Peter Webbon, Chief Executive of the Animal Health Trust, Newmarket, speaking at the Thoroughbred Racing and Breeding Seminar at Cheltenham recently. “We have seen how flu has ravaged the horse industry in Australia.”

One exotic disease with the potential to devastate the horse industry in Europe and the UK is African Horse Sickness. Brigadier Paul Jepson, Veterinary Director of the Horse Trust, a major provider of funding for scientific research and education, spoke at the seminar of the need to raise awareness of the disease.

First the good news. “You can’t catch it. One horse can’t catch it directly from contact with another horse. There is no evidence that it currently exists in Europe.”

So, why should we worried? “Firstly it is a truly horrible disease. You are unlikely to have insurance cover and the government is unlikely to offer compensation if the horse has to be slaughtered.”

The species of Culicoides biting midge that can carry AHS used to be found only south of the Mediterranean. The recent outbreak of bluetongue in cattle and sheep in the UK and Europe shows that the midge vectors are present. Last year when the risk of bluetongue disease in UK was mentioned people laughed. So what is the relevance of bluetongue to horses? “Bluetongue and African Horse Sickness are like non-identical twins” explained Jepson. “What suits bluetongue virus also suits AHS.”

The midges feed on the horse. If the horse is infected with the AHS virus, the midge becomes infected as well. The virus needs a temperature consistently above 14 degrees centigrade to mature and pass to the salivary gland. Once there, it can infect the next horse the midge feeds on.

If AHS does come to this country what could we expect? “In a word - dead horses.” Every horse that gets bitten by a midge infected with AHS is almost certain to die. The mortality rate can be as high as 90%.

Affected animals typically show signs of fever, with swelling of the face, neck and brisket. This usually progresses to great difficulty breathing and death within a week. “Essentially the horses drown in their own fluids.”

“If we are going to stop the spread of the disease we must be able to spot the signs. We need people to start to realise this could happen so any cases are identified.”

Another serious problem with this disease is carrier animals. Some can be infected without serious signs but can act as a reservoir. "We do know that rhinos can carry the disease and that donkeys and zebra are potential carriers. But there may be other species that can act as carriers. Current studies are being carried out at Pirbright to identify possible carrier species.”

The currently available vaccines are not very good. A number of horses that are vaccinated die. There is a new safer vaccine under development in France. “But don’t think it will be routinely available” he warned. “It is likely to be held in reserve to control an outbreak.”

So what is being done? The Horse Trust has set up a working party to raise awareness of this disease. “We are working with the government to produce control measures. We want to avoid control measures that involve mass slaughter.”

The virus could easily reach Europe and the UK. Midges can be blown over 100km by the wind. It has been suggested that bluetongue-infected midges might have arrived in Europe by being carried in packed flowers from Africa. The same could happen with AHS.

“African Horse Sickness could come. The current risk is assessed to be low” Jepson concluded. “If it did come it would devastate the horse industry. The problem is being addressed. But you can help - the key word is vigilance. Keep your eyes open.”

For more details on AHS see:

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Written by Mark Andrews. Available online 26.11.07.
Last updated: 26.11.07.
© Copyright Equine Science Update  2007