For Immediate Release
July 29, 2009
Public Information Officer
Montana Department ofLivestock
Season’s First Case of West Nile Virus in Horses Confirmed
State animal health officials have confirmed Montana's first case of West Nile virus (WNV) in horses, and are warning equine owners to be aware of the mosquito-borne disease and take preventative measures to reduce the risk of transmission.
On July 20, WNV was found in a 20-year-old Sanders County horse that had not been vaccinated for the disease since 2007. The disease was quickly identified, and the horse is now recovering under veterinary care – unlike some, as WNV is fatal in 30 percent of the unvaccinated horses that contract the disease.
Dr. Jeanne Rankin, assistant state veterinarian with the Montana Department of Livestock, said the appearance of the disease comes as no surprise.
"This is typically the time of year when we see the first cases of WNV in horses," Rankin said. "Horses owners who have had horses vaccinated and are actively managing mosquitoes are, by and large, not going to have any problems."
MDOL recommends that horses be vaccinated against WNV, Rankin said, including annual boosters after the initial vaccination. With WNV season typically running through September, vaccination might not be a viable option this year, although horse owners should discuss current and future vaccination options with their veterinarian.
Effective mosquito control also decreases the potential for spreading the disease. Watering troughs should be cleaned regularly, and standing water where mosquitoes breed should be managed if possible. A variety of water treatment solutions that kill fly and mosquito larvae but are nontoxic to animals are commercially available. For information on controlling mosquitoes to protect livestock, contact Greg Johnson, veterinary entomologist for the Department of Animal and Range Sciences at Montana State University (406/994-3875; firstname.lastname@example.org ).
Clinical signs of the disease in horses include loss of appetite and depression, weakness or paralysis of hind limbs, muzzle twitching, impaired vision, loss of coordination, head pressing, aimless wandering, convulsions, inability to swallow, hyper-excitability and coma. WNV mimics other neurological diseases like sleeping sickness (equine encephalitis) and rabies, and should be immediately reported so that a licensed veterinarian can make a diagnosis.
There is no specific treatment for WNV in horses, although supportive care consistent with standard veterinary practice for animals with a viral infection is recommended. Full recovery from the disease is likely for horses that were vaccinated prior to infection.
WNV was first found in the U.S. on the east coast in 1999. Since then, the disease has spread steadily westward, arriving in Montana in 2002. The disease has broad distribution in Montana, having been found in 34 counties. WNV-positive mosquitoes were recently found in Cascade County, and testing is also underway in other parts of the state.
Nationally, there have been 26 cases of WNV in humans and three cases in horses this year.
Seven cases of WNV in horses were reported in the state last year. Those numbers are down from the previous two years, when Montana had 36 (second most in the nation) and 24 cases, respectively. Nationally, the number of reported cases fell 84 percent in just two years, from 1,086 reported cases in 2006 to 178 in 2008.
West Nile Virus is a reportable disease. Any confirmed or suspected case should be immediately reported to the Montana state veterinarian at 406/444-2043 and/or USDA-APHIS Veterinary Services 406/449-2220.
For additional information about WNV, please see:
- USDA-APHIS: http://www.aphis.usda.gov/vs/nahss/equine/wnv/index.htm
- U.S Geological Survey: http://diseasemaps.usgs.gov/wnv_us_human.html
- Centers for Disease Control: http://www.cdc.gov/ncidod/dvbid/westnile/wnv_factsheet.htm