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International Spread of Disease Reviewed for World Equine Vets

Kimberly S. Brown,

Increased worldwide movement of equids means increased potential for spread of horse diseases. The impact of a disease outbreak on the health of the animals in a country, as well as the health of the country’s economy, was evidenced with the equine influenza outbreak in Australia in 2007 and 2008.

“Clinicians (veterinarians) can no longer afford to delegate their responsibilities for infectious and exotic disease control to national and international regulators,” said Des Leadon, MA, MVB, MSc, FRCVS, Dip. ECEIM, European College & RCVS Registered Consultant/Specialist in Equine Medicine, head of Clinical Pathology at the Irish Equine Centre, during a WEVA presentation with Conny Herholz, DrMedVet, PhD, Dipl. ECEIM, of the Federal Veterinary Office in Bern, Switzerland. A co-author on the paper they authored for WEVA was Dr. med. vet. Heinzpeter Schwermer, MSCVEPH, also of the Federal Veterinary Office.

“All who practice clinical veterinary medicine–in the private sector, in referral hospitals, and in the institutions and universities–have a duty of care to update themselves on exotic disease recognition and current global incidence,” they concluded.

In reality, they stated, the clinician is often the first line of defense against a foreign animal disease or disease outbreak.

“Diseases well-known in some countries can cause havoc when they are imported into naïve horse populations elsewhere,” they noted. “Climate change may also result in alteration in the geographical distribution of vector-borne equine diseases and in their transmission. Vector-borne diseases can spread rapidly via infected hosts and within vector populations and are thus difficult to control.”

Based on numbers from the Food and Agriculture Organization of the United Nations, there are 59 million horses in the world, with China leading the list at 8.08 million horses, followed by Mexico with 6.26 million; Brazil at 5.9 million; and the United States with 5.3 million.

They also looked at the trend of number of horses per 1,000 people in a population, noting that investment in equine health care trends higher when there are lower numbers of horses per thousand people.

The trend is that in developing countries there are high numbers of low-value working horses and more incidence of equine slaughter, and in developed countries with recreation/pleasure riding, competition, breeding, and racing there are fewer horses, but those are high-value animals.

For example, the global Thoroughbred breeding has 172,000 active mares in breeding programs. There are nearly 160,000 races for Thoroughbreds each year around the world.

In the sport horse industry, according to Fédération Equestre Internationale (FEI) information, in 1996 there were 350 internationally recognized FEI events. In 2006 that number had increased to 1,530.

Because of these sporting events and their associated breeding and competition programs, the worldwide movement of horses has also increased.

“There are large numbers of horses moving from North and South America to Europe,” they said. “And it’s a two-way trade.

“There’s also two-way trade coming to and from Africa, into and out of Europe,” they continued. “Ireland, for example, is the largest importer of horses from the United States. There are a large number of South American horses imported to Italy.

“This means countries are exposed to disease risk from different sources,” they said. “Despite significant scientific expertise, there have been significant ourbreaks of disease.”

They said when an exotic disease is imported into a naive population, there is an explosion of disease. That was the exact result of equine influenza being introduced in Australia.

And it’s not just horses that carry disease to different locations, it can be the trade or movement of equine products, such as plasma, semen, or embryos.

For example, the 2006 outbreak of equine infectious anemia (EIA) in Ireland was the result of illegally imported equine plasma carrying EIA. That plasma was used on a farm and created a cluster of 21 cases.

There also has been equine disease outbreaks because of importation of vectors that carry a disease. “Once a disease is introduced into a country and (that country has the appropriate carrier) vector, you have rapid spread of disease that is difficult to control,” the authors stated.

Examples of this have been EIA in Ireland, West Nile virus in the United States, African horse sickness in various parts of the world, and Eastern, Venezuelan, and Western equine encephalitis. Vectors can include ticks, gnats, flies, and mosquitoes.

They noted that spread of disease has occurred through both legal and illegal trade of horses and their biological products (semen, embryos, plasma).

It was also said that migratory birds can play an important role in the introduction of foreign animal diseases. Birds were “highly suspected as a principal means of introduction of WNV in the United States.”

The take-home message was outlined below:

A Clinician’s Responsibilities *

  • Be aware risks associated with international trade and their importance.
  • Be aware of import requirements and legislation and the global situation of contagious, notifiable equine diseases.
  • Be aware of syndromes in the world.