PULLMAN, Wash. — Washington State University veterinarians and disease investigators are closely watching the advance of West Nile virus toward the West and are strongly encouraging horse owners to have their animals vaccinated.

West Nile virus is spread by the bite of an infected mosquito. Mosquitoes become infected after feeding on infected birds and can then transmit the virus to people, horses, many birds, and some other animals. Dogs and cats very rarely develop the disease. The majority of people and horses exposed do not develop the clinical disease either.

There is no evidence to suggest that West Nile virus can be spread from person to person or from animals to people.

“There is a vaccine available for horses,” said Melissa Hines, equine medicine specialist for the WSU veterinary teaching hospital. “Right now it is available on a conditional use permit meaning that although it is safe, not all of the testing has been completed to determine how well it prevents disease. Currently, the vaccine can only be administered by a veterinarian.”

Hines said WSU has laid in supplies of the vaccine as have veterinarians throughout the state.

“Prevention of the disease is vital and owners can do a lot to protect their animals in addition to a vaccine,” said Hines. “People should eliminate standing water; decrease overnight lighting in stall areas; consider housing horses inside from dawn to dusk, the peak mosquito activity time; and realize the use of fans, insect repellents, and sheets may also be of help.”

One area of interest is in Indiana where veterinary officials have documented at least eight horses killed by West Nile virus and perhaps hundreds more sickened. The disease outbreak occurred in two heavily Amish regions where vaccinated horses are rare.

The USDA’s National Veterinary Services Laboratories has confirmed 645 cases of West Nile virus infection in horses nationwide. Horses ranged in age from 4 months to 38 years, with an average age of 14 years. Approximately 30 percent of the infected horses die from the disease or are humanely euthanized. For additional information on the 2002 cases, WSU officials suggest visiting http://www.aphis.usda.gov/oa/wnv/wnvstats.html.

Hines and veterinary pathologists of the Washington Animal Disease Diagnostic Laboratory (WADDL) at WSU urge the public to take the West Nile virus advance in perspective and to not panic.

“This is just a new disease to this continent that we expect remain relatively rare as diseases go,” said Professor Tom Besser, director of WADDL. “Remember that human flu viruses spread across this country every year and are responsible for an average of 20,000 deaths per year. West Nile certainly deserves our concern and careful monitoring, but it is not a reason for the public to become overly concerned or panic.”

Nationwide, the Centers for Disease Control has reported 14 U.S. deaths this year from the West Nile virus in 296 confirmed cases.

Besser said WADDL has all testing procedures in place for animals suspected of having West Nile virus, especially birds and horses. The efforts at WSU are the latest in continuing efforts to provide up-to-date disease diagnostic services that are paralleled at a network of other laboratories across the U.S. So far, WSU has tested a small number of horses and one brain tissue sample for West Nile virus and all tests have been negative.

The virus first surfaced in New York in 1999 and was identified by a veterinary pathologist at the Bronx Zoo. The virus has been found in every state east of the Rocky Mountains; most recently it has been identified in Wyoming and Montana.

On rare occasions, West Nile virus infection can result in a severe and sometimes fatal illness in humans characterized by an inflammation of the brain. The risk of severe disease is higher for people 50 years of age and older.