Study: West Nile virus cost equine industries in Colorado, Nebraska millions in 2002

Last year, West Nile virus cost equid owners in Colorado and Nebraska more than $1.25 million, while preventive measures are estimated to have cost an additional $2.75 million, according to a study evaluating the economic impact of WNV on the Colorado and Nebraska equine industries in 2002.

Released in May, the study estimated that the total cost attributable to death or euthanasia of equids from WNV infection was $600,660, the estimated revenue lost by owners because of lost use associated with WNV was $163,659, and the estimated cost attributable to treatment in the two states was $490,844.

In 2002, 378 and 1,100 equine cases of West Nile infections were confirmed in Colorado and Nebraska, respectively.

Until now, no other comprehensive national or regional estimates of WNV's economic impact on the equine industry have been published. The study was a cooperative effort among researchers at the Department of Agriculture, Colorado State University, Nebraska State University, and the University of Pennsylvania.

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.

"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 research associate at CSU who participated in the study.

"This collaborative study is the first to determine specifically what this disease is costing the equine industry," she said.

To calculate the economic impact associated with death, the researchers multiplied using the estimated number of equids that died or were euthanatized 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 euthanatized as a result of the virus. The average value of one equid for both states combined was estimated at $1,420 on the basis of data from the National Agricultural Statistics Service.

Researchers estimated the number of days of lost use for equids that had fully recovered (80 percent of surviving equids) from WNV infection 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.

The value of lost use was estimated using the average sale value of an equid ($1,420) divided by the number of days of life expectancy adjusted to current dollars and the weighted average cost of maintaining an equid during the period of lost use.

To determine the cost of treating infected equids, the researchers placed each case in a category of mild, moderate, or 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 determined that it costs approximately $200 to treat animals with mild disease, $400 for those with moderate disease, and $250 for equids with severe disease. Severe cases cost less, on average, because many severely infected equids were likely euthanatized before incurring high treatment expenses.

A two-part WNV vaccine for equids was developed in the summer of 2001 to aid in the prevention of infection. Because 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 vaccination, but it can be estimated by determining the approximate number of equids vaccinated and the average cost of the vaccinations.

Approximately 47 percent of equids with WNV 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 WNV vaccination likely exceeded a combined $2.75 million in Colorado and Nebraska in 2002.

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

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 by using a telephone survey of 493 randomly selected equine owners whose animals were treated for West Nile virus infections in 2002.

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.

The entire report can be viewed and/or downloaded at http://www.aphis.usda.gov/animal_health/nahms/equine/downloads/wnv2002_CO_NB.pdf (PDF).