Nationwide West Nile Case Count Continues to Rise

Nationwide West Nile Case Count Continues to Rise

According to the USGS disease maps, 364 cases of equine WNV had been confirmed at last update (Sept. 25).


As fall begins and temperatures slowly drop, the number of confirmed equine West Nile virus (WNV) cases around the country continues to rise.

According to the U.S. Geological Survey disease maps, 364 cases of equine WNV had been confirmed at last update (Sept. 25). The current case total is the highest since 2007, when 468 horses were confirmed WNV-positive. The current total will likely rise, as mosquito season is not over in many parts of the country.

Iowa, Kentucky, Louisiana, and Virginia have all confirmed WNV cases recently.

Iowa--The Iowa Department of Agriculture and Land Stewardship issued a statement Sept. 28 indicating more than 20 horses in that state had tested positive for WNV thus far in 2012. The statement reported only one case was confirmed in Iowa in 2011.

"Horse owners are encouraged to make sure they get their animals vaccinated and keep the vaccination up-to-date," Bill Northey, Iowa secretary of agriculture, said in the statement. "The cases we are seeing are in horses that have not been vaccinated or are not current on their vaccinations, so we are encouraging owners to talk to their veterinarian and make sure their animals are protected."

Kentucky--Kentucky animal health officials confirmed an additional case of equine WNV, according to a Sept. 28 statement from Kentucky Equine Programs Manager E.S. "Rusty" Ford.

An unvaccinated 26-year-old Quarter Horse stallion from Madison County began showing clinical signs--including recumbency (unable to rise after lying down), hyperesthesia (hypersensitivity to touch and sound), and miotic (constricted) pupils--on Sept. 25 and was euthanized the same day. Ford said the horse had no vaccination history.

Kentucky has now confirmed 13 WNV cases on 12 premises in 11 counties (Bourbon, Franklin, Garrard, Henderson, Henry, Laurel, Madison, Metcalfe, Scott, Shelby, and Warren) in 2012. Six are recovering while seven have been euthanized. Ford reported that nine affected horses were unvaccinated, three were partially vaccinated, and one was reportedly vaccinated.

Louisiana--On Oct. 1, Laura Pursnell-Lindsay, public information director for the Louisiana Department of Agriculture and Forestry, told that 60 WNV cases had been confirmed in that state so far this year.

Virginia--On Sept. 28, the Virginia Department of Agriculture and Consumer Service (VDACS) confirmed the commonwealth's first equine WNV cause of 2012. According to a press release from the agency, the 9-year-old Morgan gelding from Loudon County had not been vaccinated against the disease for at least three years. He developed clinical signs on Sept. 11 and was subsequently euthanized.

In the release, Joe Garvin, DVM, head of VDACS' Office of Laboratory Services, urged horse owners to check with their veterinarians about vaccinating their animals for WNV.

"WNV is a mosquito-borne disease," he said. "We generally start seeing our first cases in August and September. The disease is preventable by vaccination, as is Eastern equine encephalitis, so many veterinarians recommend vaccination at least yearly and in mosquito-prone areas every six months."

Clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations (twitching); hyperesthesia; changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional somnolence (drowsiness); propulsive walking (driving or pushing forward, often without control); and "spinal" signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia (incoordination on one or both sides, respectively). Equine mortality rate can be as high as 30-40%.

The American Association of Equine Practitioners recommends all horses be vaccinated against WNV at least annually and possibly more frequently, depending upon geographic location. Many veterinarians are urging horse owners to ensure their animals' WNV vaccines are up to date, given the rise in case numbers this year.

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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