West Nile Virus (WNV) Reported in Pennsylvania; Vaccination Is Recommended

Prepared by:  A. Swinker, Cooperative Extension Horse Specialist,  References The Horse, West Nile Fact Sheet and Pennsylvania West Nile Virus Control Program

Infection with the West Nile virus (WNV) causes a potentially fatal encephalomyelitis

(Inflammation of the brain and spinal cord). WNV affects a variety of animals, including birds, horses, humans, and some other mammals. In 2000, West Nile virus appeared for the first time in Pennsylvania in birds, mosquitoes and a horse. To combat the spread of West Nile virus, which is transmitted by mosquitoes, Pennsylvania has developed a comprehensive network. This network, which covers all 67 counties, includes trapping mosquitoes, collecting dead birds and monitoring horses, people.   Please explore this site to find out more about how you can help, to learn about West Nile virus or the latest surveillance update from your area. http://www.westnile.state.pa.us/

Signs of WNV in horses include ataxia, weakness of the hind limbs, laying down, muscle tremors, convulsions, and coma. Diagnosis is typically achieved by one or more blood tests and by ruling out other causes of neurologic disease.  Treatment is primarily supportive, and approximately two-thirds of affected horses recover from infection.  Some horses (approximately 40%) will have residual neurologic deficits after recovering from WNV.

There is no specific treatment or cure for infected horses. Veterinary care includes administration of anti-inflammatory drugs and intravenous fluids (if necessary). Supportive care is exceedingly important for infected horses to ensure adequate food and water intake, protect the safety of the horse (to prevent injuries in ataxic horses), and to prevent pressure sores in recumbent horses. Some veterinarians have attempted treating horses with antiviral drugs such as interferon and passive antibody products for WNV, but published clinical trials demonstrating efficacy or safety of this approach are lacking at present.

Preventing WNV in horse involves vaccination and minimizing exposure of your horse to mosquitoes and infected birds. Since there is no cure for WNV, prevention is the key to minimizing the chances of horses becoming infected with the virus. Current preventative measures include vaccination, management strategies, and ensuring your horse is in optimal health. The American Association of Equine Practitioners (AAEP) recommends vaccinating all horses against WNV. Unvaccinated adult horses should be vaccinated twice, four to six weeks apart. Thereafter, horses can be re-vaccinated based on risk of exposure, up to once every four months. In the north it is recommended to vaccinate horses in the spring prior to peak mosquito levels.

In addition to vaccination it is important to minimize mosquito populations near your horses by eliminating breeding and resting areas and keeping mosquitoes away from horses. For example, reduce or eliminate sources of stagnant or standing water, remove muck from areas near the horses, stable your horses during peak mosquito periods (i.e., dawn and dusk), use equine approved mosquito repellents, place fans inside the barns or stalls to maintain air movement, and avoid using incandescent light bulbs inside stables at night. Instead, place incandescent bulbs away from the stables. This will attract the mosquitoes to areas outside the stable.

Report any dead birds—particularly crows, blue jays, owls, and hawks—to your local Department of Health as they might want to test the birds for West Nile virus.