Colorado State Equine Veterinarians Take Lead in West Nile Virus Studies, Compiling Information from Two Western States

Equine veterinarians at Colorado State University’s James L. Voss Veterinary Teaching Hospital are currently involved in three research projects to analyze the statistics from this year’s outbreak of West Nile virus in two Western states.

One study will assess the long-term status of horses that had the virus. With the help of several second year veterinary students and the cooperation of the state veterinarian’s offices of Colorado and Nebraska, the CSU veterinarians hope to follow up with 500 to 600 horse owners in both states to gather information about their individual horses.

"The state veterinarian’s offices had the client contact information on these cases but lacked the manpower and time to follow up with inquiries on long term outcomes and details about the cases such as vaccination status and treatment," said Dr. Tricia Salazar, one of the equine veterinarians working on the research. "We were able to enlist the help of about two dozen second year veterinary students to help us draft a survey, make the calls to horse owners and gather the details about their cases. We couldn’t have done it without their help. They supplied the "legwork" we needed to get this analysis done in a timely manner."

With the information from this research, Dr. Salazar expects to have a clearer picture of last summer’s outbreak, especially the numbers of horses affected who were unvaccinated or incompletely vaccinated and the survival rate.

"We want to know how many horses were affected, whether they were vaccinated, unvaccinated, or incompletely vaccinated; the age, breed, sex and health condition of the affected horses and, of course, the outcome," Salazar said. "This will be the first time all this information has been gathered, evaluated and statistics presented for horses in the western states. This should give us some vital information to use in planning our protection for next summer."

A second study will compare the antibody response in horses who contracted the West Nile virus and were unvaccinated with those who were vaccinated. Dr. Ann Davidson, who is heading up this project, has been working with Dr. Eileen Ostlund at the National Veterinary Services Laboratories to determine the tests that will be performed on the serum collected as part of this study. Dr. Davidson will follow up this spring to again gather samples from study horses and further gage the antibody level.

"West Nile virus in horses has proven to be a deleterious and potentially fatal disease," said Dr. Davidson. "Because it is relatively new in the United States, and especially in Colorado, there is much to be learned about the disease and how to prevent a horse from contracting it. We hope that by performing this study, we will better understand the efficacy and duration of protection that the vaccination confers. This information will be useful for planning proper vaccination schedules to help prevent disease occurrence."

A third study targets information from veterinarians about costs, cases, treatments and outcomes related to West Nile virus patients. About 850 surveys have been distributed to veterinarians in Colorado and Nebraska requesting information about the number of West Nile cases treated, what forms of treatment were administered and, importantly, the case fatality rate.

"The clinical signs exhibited by infected horses vary in their severity from one horse to the next," said Dr. Josie Traub-Dargatz, who is overseeing all three projects at Colorado State. "Some horses are affected very little, displaying only vague symptoms while other horses are found down and may not be able to rise, and others suffer acute death. Right now, we don’t know why some horses become so ill and others do not. We’re hoping to find some answers to these questions."

The CSU veterinarians say they hope to have numbers from these studies very soon.

"We felt it was very important for CSU researchers and students to lend what expertise and help we can provide to solving the mysteries surrounding the occurrence of the virus in horses in the western states," said Dr. Josie Traub-Dargatz. "With this information, we hope to be able to alert horse owners to the early signs of West Nile virus and to advise owners of how severe the disease can be. This will allow them to make more informed decisions about immunization and other health care-related issues for their horses."