April 28, 2008

The growing threat from African Horse Sickness (AHS) and West Nile Virus (WNV) will be discussed at a seminar in Britain in June.

The two diseases are considered a serious threat to Britain's horse population, with climate change increasing the risk of both diseases emerging in the UK.

The June 23 conference is being organised by the Thoroughbred Breeders' Association and The Horse Trust.

AHS is considered the most devastating horse disease on the planet. Up to 90% of infected horses die sometimes within 48 hours of infection. It has been known since horses were introduced to southern Africa in the 17th century and large sporadic outbreaks have occurred since then.

It is related to the bluetongue virus of sheep and cattle, which has already made inroads in Europe. AHS is carried and transmitted to horses by certain members of the Culicoides family of midges.

These common biting midges occur throughout Britain and are more usually known for causing sweet itch. They travel on the wind like aerial plankton and, in laboratory conditions, have been known to fly for 10 hours at a time.

AHS has yet to be seen in Britain, but because sheep and cattle have been infected with bluetongue it is now believed that, contrary to previous thinking, AHS could also spread if it arrived in the UK.

There is no vaccine available to control AHS at present. If a case occurred in the UK, current control regulations would mean a total shut-down of the £4 billion equestrian industry, affecting racing, eventing, show-jumping, pony club and leisure riders.

The other emerging threat is West Nile Virus, an encephalitis disease of horses spread by mosquitoes. This has already proved a scourge in North America and has the added risk that infection can cross the species barrier into humans, where it can prove fatal.

Nearly one in three horses (up to 62.5%) affected by the disease either die or have to be put down although those which survive the disease usually make a complete recovery.

Progression from first signs to severe disease requiring euthanasia has been reported to take as little as 24 hours in one case following experimental infection but in outbreaks several days of clinical illness have been reported.