With six more horses in Colorado showing symptoms of Equine Herpesvirus (EHV-1), the outbreak looks ever more threatening. Agricultural officials and veterinarians throughout the United States and Canada are warning horse owners and putting biosecurity measures in place.
Two Colorado horses were confirmed with the virus in the last week, both having attended the the National Cutting Horse Association's Western National Championships in Ogden, Utah.
One case has also been confirmed in Washington, in a horse admitted to the Washington State University veterinary teaching hospital. The horse was admitted for observation in relation to to other issues, but developed a fever and was later found to have attended the Utah event.
Other states are assessing and monitoring the situation, as horses who attended the championship returned to several states after competition.
The Colorado Department of Agriculture said it was working with the Utah State Veterinarian to investigate the location of the Ogden championships "as a point of interest for the infection".
Horse owners who took animals to Ogden are being urged to notify their veterinarian and isolate and monitor their horses for clinical signs of the disease.
The department says individual horse and barn biosecurity is important, as some horses may not show signs of the disease but may still be a carrier. Those owners are also encouraged to restrict movement of their horses.
"This disease can have tremendous affects on the horse community and I encourage horse owners to be vigilant about the disease prevention methods they use within their premises," said Colorado state veterinarian Dr Keith Roehr.
EVH-1 can transfer from nose-to-nose contact. It can also be spread by contaminated tack, equipment, and people's clothing. In addition, the virus can be spread on the air for a limited distance.
EHV-1 can cause respiratory and neurologic disease and death in horses.
Symptoms include fever, decreased co-ordination, nasal discharge, urine dribbling, loss of tail tone, hind limb weakness, leaning against a wall or fence to maintain balance, lethargy, and the inability to rise.
While there is no cure, the symptoms of the disease may be treatable.
Meanwhile, the Colorado State University Veterinary Teaching Hospital has moved to restrict equine and camelid client movement to the hospital for appointments.
Non-emergency cases are being rescheduled as a precaution. The hospital urged horse owners to avoid transporting their horses at this time.