Take Steps Now to Prevent West Nile Virus in Horses

Pennsylvania Agriculture Secretary George Greig has urged horse owners to consult their veterinarians about options for West Nile virus (WNV) prevention before mosquito season begins.

"From recreational trail riders and trained competitors to top-notch breeding and racing, Pennsylvania's equine industry represents an important segment of our state's leading economic driver - agriculture," said Greig. "Animal health is a top industry priority, and I encourage horse owners to speak to their veterinarians about protecting their animals against encephalitic diseases like West Nile Virus."

Equine encephalitic diseases are transmitted by mosquitoes and cause inflammation of the brain. Mosquitoes become more active with warm weather in early spring.

First confirmed in the United States' horse population in 1999, WNV infection is responsible for equine clinical signs including flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations (twitching); hyperesthesia, or hypersensitivity to touch and sound; 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 USDA Animal and Plant Health Inspection Service reported 83 cases of WNV in U.S. horses in 2011.

Vaccines are available to help prevent WNV and other equine encephalitic diseases such as Eastern and Western equine encephalomyelitis. Vaccines are usually administered in February or March prior to mosquito season. Horse owners should talk with their veterinarians to determine the best time to start the vaccination process.

Greig cautioned that vaccination of horses is not a guarantee of protection against infection. The best way to prevent infection of WNV is to reduce the risk of exposure to mosquitoes by eliminating mosquito breeding sites.

He suggested several steps horse owners can take to reduce horses' mosquito exposure:

  • Reduce the number of birds in and around the stable area. Eliminate roosting areas in the rafters of the stable. Certain species of wild birds are the main reservoir for the virus.
  • Check the property for dead birds, especially crows. Any suspicious birds should be reported online to www.westnile.state.pa.us or by calling the Department of Environmental Protection at 717-346-8238 (residents of other states should report suspicious dead birds to animal health authorities in their area) . Use gloves to handle dead birds and place the birds in plastic bags. If not submitting the bird for testing, the bagged bird can be placed in the trash. Wash hands thoroughly with soap and water after discarding the dead bird.
  • Topical preparations containing mosquito repellents are available for horses. Read the product label before using and follow label instructions. Fly sheets, masks, and leg wraps are also available.
  • Dispose of tin cans, plastic containers, buckets, ceramic pots or other unwanted water-holding containers on the property. Pay special attention to discarded tires, which can collect water and become mosquito breeding sites.
  • Drill holes in the bottom of recycling containers left outdoors. Containers with drainage holes located only on the sides collect enough water to act as mosquito breeding sites.
  • Clean clogged roof gutters every year. Millions of mosquitoes can breed in roof gutters each season.
  • Turn over plastic wading pools and wheelbarrows when not in use.
  • Empty and refill outdoor water troughs, buckets, and birdbaths every few days so water does not stagnate.
  • Aerate ornamental pools or stock them with fish. Water gardens can become major mosquito producers if they are allowed to stagnate.
  • Use landscaping to eliminate standing water that collects on your property, especially near manure storage areas. Mosquitoes can breed in any puddle that lasts for more than four days.

For more information contact the Pennsylvania Department of Agriculture's Bureau of Animal Health at 717-783-6897 or visit www.westnile.state.pa.us.

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