Report Released About the Economic Impact of West Nile Virus on Colorado and Nebraska Equine Industries

A study led by researchers at Colorado State University determined that the effects of West Nile virus cost equine owners in Colorado and Nebraska more than $1.25 million in 2002, and prevention costs for WNV vaccinations likely exceeded an addition $2.75 million for the equine industry last year. In 2002, Colorado reported 378 and Nebraska reported 1,100 confirmed cases of WNV in equids, a family of animals that includes horses, ponies, donkeys and mules.

The study estimated that the total cost attributed to death or euthanasia of equine WNV cases was $600,660, the estimated revenue lost by owners because of lost-use associated with WNV was $163,659 and the estimated cost attributed to the treatment of equine WNV cases in the two states was $490,844.

The entire report can be viewed and/or downloaded at

"To date, no other comprehensive national or regional estimates of WNV’s economic impact on the equine industry have been published," said Dr. Josie Traub-Dargatz, veterinarian and professor of clinical sciences at Colorado State and principal investigator of the project. "Determining the economic impact of the disease is important for prioritizing current and future research as well as management and control efforts."

The study, published by coauthors from the United States Department of Agriculture’s Animal and Plant Health Inspection Service, was a cooperative effort among researchers from Colorado State, the USDA, the Colorado and Nebraska State Veterinarians and the Veterinary schools at the University of

Pennsylvania and the University of Nebraska. The purpose of the report was to evaluate the economic impact of WNV on the Colorado and Nebraska equine industries in 2002.

"To fully understand the impact of West Nile virus infections in equids, it is important to also consider variables beyond the cost of treating the disease, such as the cost of not being able to use the animal during its illness and recovery and the cost of disease prevention," said Dr. Tricia Salazar, a Colorado State University veterinarian who participated in the study. "This collaborative study is the first to determine specifically what this disease is costing the equine industry."

Economic impact associated with death was calculated using the estimated number of equids that died or were euthanized because of WNV multiplied by the average sales value of the animals. The fatality rate for the 1,478 equine WNV cases was estimated to be 29 percent, suggesting approximately 423 equids died or were euthanized due to the virus. The average value of one equid for both states combined was estimated at $1,420 based on data from the National Agricultural Statistics Service.

The number of days of lost-use for equids that had fully recovered (80 percent of surviving equids) from WNV infection was estimated by using data collected from owners. The average number of days of lost-use for infected equids was 22 days. The cost of lost-use attributed to WNV for the 862 equids that recovered totaled $8.63 per day. The researchers added that, if it were possible to include an estimate of the lost-use for the 20 percent of equids that had not yet fully recovered, then the cost would increase.

To determine the cost of treating infected equids, the researchers placed each case in a category of mild, moderate and severe. Of the cases studied, 8 percent were mild, 58 percent were moderate and 34 percent were severe. Veterinarians then estimated the cost of treatment for each category and derived that it costs approximately $200 to treat mild cases, $400 for moderate cases and $250 for severe cases. Severe cases cost less, on average, because many severely infected equids were likely euthanized before significant treatment expenses occurred.

A two-part WNV vaccine for equids was developed in the summer of 2001 to aid in the prevention of infection. Since the percentage of vaccinated equids within Colorado and Nebraska is unknown, it is not possible to calculate the exact cost of prevention of WNV by vaccine, but can be estimated by determining the estimated number of equids vaccinated and the average cost of the vaccinations. Approximately 47 percent of equine WNV cases in Colorado and Nebraska received at least one WNV vaccination in 2002, according to the owner survey. From this information, researchers estimate that prevention costs of WVV vaccination likely exceeded $2.75 million in Colorado and Nebraska in 2002.

The costs of prevention other than vaccination are not included in the report, such as insecticide spraying, eliminating standing water and other measures.

Information used for the study regarding confirmed equine WNV infections was obtained from the Nebraska and Colorado State Veterinarians. From this information, the researchers collected data using a telephone survey of 493 randomly selected equine owners whose animals were treated for West Nile virus in 2002. The survey focused on the WNV vaccination status of affected animals, observed clinical signs, recovery, treatments and prevention measures. Data gathered were combined with equid population and sales value estimates from the USDA’s National Agricultural Statistics Service and the estimated cost of equid care from the American Horse Council.

A second survey collected information from 248 randomly selected veterinarians in both states that focused on the number of equine WNV cases seen, treatments administered and treatment costs.

Because only laboratory confirmed cases were considered in the study, the researchers stressed that estimated costs represent a conservative estimate of the actual cost of WNV to the equine industry.

West Nile virus primarily affects equids, birds and humans. The virus is spread by mosquitoes and results in encephalitis or inflammation of the brain. In horses, WNV has varying effects, leaving some animals experiencing short-lived neurological problems and other suffering from fatal encephalitis.

Since first recognized in the United States in New York in 1999, WNV has spread rapidly across the country, with seven states reporting 800 or more confirmed equine cases in 2002. The report’s researchers indicate that the actual numbers of WNV cases are likely higher than those reported since many suspected cases were not confirmed in a laboratory.

While vaccination reduces the chance that an animal will contract the virus, it does not completely protect all fully vaccinated horses under field conditions. Thus limiting animals’ exposure to mosquitoes is an effective way to avoid illness in horses. The USDA recommends eliminating pools of standing water, using mosquito repellant and keeping the animals indoors during the dusk and dawn hours.