By Keith Coffman
DENVER (Reuters) - An equine herpes outbreak has widened to include eight Western U.S. states, with 33 horses confirmed to have the highly contagious disease, the U.S. Department of Agriculture said on Thursday.
The outbreak comes just as the prime season for riding shows, sales and rodeos is starting, resulting in the forced cancellation of scores of horse events.
All but one of the 33 confirmed cases involve horses that attended a National Cutting Horse championship competition held in Ogden, Utah, from April 29 to May 8, an event that health officials have identified as the source of the outbreak.
A total of 308 horses were present at the Utah event, and another 689 have been exposed by secondary contact or proximity, according to the Department of Agriculture (USDA).
Seven of the infected horses have died or were euthanized, according to the USDA statement.
Equine herpes virus (EHV-1) is a highly contagious disease spread by horse-to-horse contact or through contaminated equipment, clothing and hands, officials said.
Horses cannot infect humans but for the animals the symptoms of the virus include respiratory problems and hind-leg weakness, decreased coordination, nasal discharge and fever.
Earlier this week, it appeared the outbreak had reached at least six states, but it was unclear how many horses were infected. In recent days some states increased their count of how many horses were sick with the virus.
A cutting horse competition, such as the one where the outbreak originated, is an event where horse and rider must separate an animal -- such as a steer or heifer -- from a cattle herd and keep it away for a period of time.
California has the most confirmed cases of equine herpes from this outbreak. Thirteen horses from the state have been confirmed as infected, up from a count of 10 earlier, said Steve Lyle of the state's Department of Food and Agriculture.
"We're continuing to investigate at this point. It's probably too soon to say where we are in terms of case load. We hope that we're near the end," Lyle said.
In Colorado, laboratory testing has confirmed eight cases, the state agriculture board reported.
Two of the infected animals in Colorado and one in California were euthanized, officials said.
The other states with confirmed cases are Utah, Idaho, Oregon, New Mexico, Texas and Washington, the USDA said.
The American Horse Council and the American Association of Equine Practitioners said on Thursday they asked the USDA to collect and disseminate data on the total number of cases, so horse owners can get a better handle on the outbreak.
Already, cutting-horse competitions scheduled for this weekend in nine states have been canceled, and two equestrian reining and jumping clinics in Colorado have been called off.
(Editing by Alex Dobuzinskis and Peter Bohan)