CRUNCHING THE NUMBERS:
CALIFORNIA’S EQUINE WNV MORTALITY RATE
By: John V. Wood

California horse owners have been keenly aware of the problem presented by the West Nile virus, but the problem is
taking a deadly turn.  The virus has been discovered in all but one of the Golden State’s 58 counties, leaving only Del
Norte County without any reported cases.
According to the California Department of Health Services, 42.2% of reported equine WNV cases in 2004 were fatal. Dr.
Gregory L. Ferraro, director of the Center for Equine Health at the University of California-Davis’ College of Veterinary
Medicine, says the equine mortality rate is probably exacerbated by several factors.
“There's an economic barrier here,” said Dr. Ferraro. “Many people simply can't afford to call out a veterinarian, have
their horses vaccinated, and then have the veterinarian come out again to give the second shot. As a result, when
those horses become infected with West Nile, the owners generally elect to have the animals put down rather than have
them treated.” One WNV vaccination does not completely protect a horse, so state officials recommend a second
vaccination.  Depending on where you live in California, one vaccine injection usually costs around $100.
Another disturbing factor connected with WNV in California is the problem of veterinarians underreporting fatal equine
cases to state officials. “As soon as [the veterinarians] saw the symptoms, they went ahead and put the horse down,
and didn’t even report the cases,” said Dr. Ferraro. “There is a great possibility we have many more cases of death by
West Nile than we already have documented.” Dr. Ferraro feels it is very important to compile the complete list of fatal
equine WNV cases as soon as humanly possible.
Dr. Ferraro said California is doing a great job bridging the language barrier as well, helping non-English speaking
horse owners and caretakers identify WNV. The state has developed a website (http://westnile.ca.gov/), featuring
announcements in English and Spanish.  Printed materials are provided in a number of languages, including English,
Portuguese, Spanish, Chinese and Russian. Pictures and videos are available to show horse owners what WNV
infection looks like, why they should vaccinate their horses, and how they can go about doing it.
However, Dr. Ferraro thinks addressing the cost of WNV vaccinations should be California’s focus right now. “A lot of
the veterinary associations and riding clubs in California have organized low cost vaccination clinics, to be able to
vaccinate horses for people who couldn’t afford the $200 vaccination fee. I know for us, if we want to cut down the
deaths and increase the vaccinations, this is something we’re going to have to address.”

Sources:
*Dr. Gregory L. Ferraro, director, Center for Equine Health, UC-Davis School of Veterinary Medicine. University of
California, Davis, CA 95616 Phone: 530-752-6433 Fax: 530-752-9379. E-mail: glferraro@ucdavis.edu

*California’s West Nile Virus Website (http://westnile.ca.gov/)

*Equine West Nile Virus handout from the California Department of Food and Agriculture (can be provided upon
request) – acquired from http://www.cdfa.ca.gov