Britain's £4bn a year equestrian industry must be prepared for exotic diseases to hit the naïve population - but does not need to panic. This was the message delivered to 200 delegates at last week's Emerging Exotic Diseases seminar in Newmarket, hosted by The Thoroughbred Breeders Association and The Horse Trust.

The seminar focused on two particular diseases: African horse sickness (AHS) - described as "the most devastating horse disease on the planet" and West Nile virus (WNV) which has been found to be transmissible to humans.

African horse sickness is endemic in South Africa, where devastating but sporadic outbreaks - now becoming more frequent - have been linked to movement of zebra between the increasing numbers of game parks. Professor Alan Guthrie highlighted the clinical signs of the disease and the ways in which South Africa undertakes treatment and control.

But he warned: "There is no specific treatment for AHS. Affected animals should be provided with supportive therapy, nursed and rested as the slightest exertion may result in death. Animals that survive should be rested for at least four weeks following recovery before being returned to light work. They should also be carefully monitored for complications such as piroplasmosis."

West Nile Virus appeared in the USA in 1999, spread rapidly through equines in all 48 mainland states and peaked in 2002 with some 15,000 cases, said Dr Josie Traub Dargetz of Colorado State University USA.

"Since then, although endemic, the number of annually diagnosed cases has fallen, probably due to naturally acquired immunity, preventive management, and frequent use of WNV vaccination," she said.

"Management and control measures in the U.S.A. include the use of mosquito control through source reduction by larviciding and adulticiding, repellents (topical pyrethroids), and vector- resistant housing."

Tolerance of WNV is more obvious in South Africa. "Epidemics of neurological disease caused by WNV and which were characterized by ataxia, weakness, recumbency, muscle fasciculation and high case-fatality rates have recently been reported amongst horses in North America, North Africa, Asia and Europe. In contrast, WNV infection is endemic in South Africa but neurological disease has only very rarely been observed in horses infected with WNV in the country," Prof Guthrie added.

WNV is already controlled in the US by vaccination but, while a range of vaccines for AHS is available in South Africa, these have not been found suitable for use in Europe. Dr Jules Minke of Merial France explained: "Notwithstanding the evident success of the polyvalent modified live vaccines against AHS in endemic areas, there are concerns about their use in epidemic situations because of their inherent biological safety risks." Work is, however, under way to develop a vaccine which would be acceptable.

In the UK, Defra is charged with implementing control procedures should either disease be diagnosed. Matthew Hartley, Deputy Head of Exotic Notifiable Diseases, told the conference: "Defra is participating in an equine-industry-led working group to develop a UK African Horse Sickness Strategy. The strategy takes forward current European legislation and describes how it would be implemented in partnership should African Horse Sickness arrive in the UK. This is currently in the drafting phases and will be available for consultation later this year.

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