The West Nile virus (WNV) is hosted by birds and spread by mosquitoes. When an infected mosquito bites a horse, the virus enters the bloodstream and spreads to the spinal cord and brain, causing widespread inflammation. WNV can also be transmitted from mare to foal.
Clinical signs of the disease typically develop three to 15 days after initial exposure. These include fever, a wobbly gait, stumbling and aimless wandering, weakness in the hind limbs, lethargy, an unwillingness to eat, an inability to get up, teeth grinding and excessive sweating.
Contact your vet as soon as you spot any of these symptoms, especially those that are neurological such as a wobbly gait or muscle trembling. A blood test will be needed to rule out rabies, equine protozoal myeloencephalitis and other neurological diseases.
There is currently no cure for horses infected with WNV. Your vet will administer anti-inflammatory drugs and, if necessary, intravenous fluids. Thereafter, it’s up to you to do all you can to nurse the sick horse. Provide plenty of food and water, protect the horse from self-inflicted injuries, and prevent pressure sores if the animal cannot get up by placing it on an old mattress.
Bear in mind that 10% of horses are likely to experience a relapse, so monitor the animal for at least a month after it has recovered.
Unfortunately approximately 40% of horses unable to stand are more likely to succumb to WNV. In addition, about 40% of horses that do recover from the infection experience problems such as awkward gait after recovery.
Vaccination is the first step in prevention. Since horses younger than five years and older than 15 are at a higher risk of contracting WNV, these should be vaccinated twice a year.
Adult horses previously unvaccinated or with an unknown vaccination history should be vaccinated twice, the second time four to six weeks after the first vaccination. Thereafter they should receive a booster annually. Many vets administer WNV vaccines to pregnant mares, as the consequences of WNV infection outweigh the risk of complications that might arise from vaccination.
A pregnant mare previously vaccinated should be vaccinated four to six weeks before foaling. Foals of vaccinated mares can be inoculated in three stages from the age of four months. The third dose should be administered at 10 to 12 months of age before the onset of the next mosquito season.
Keep the environment clean!
Good stable management will help to reduce the risk of WNV:
- Get rid of mosquito populations near your horses. If stagnant water is in the vicinity, consider installing a pump to circulate the water;
- Remove any dirt from areas near the horses and stables. Keep grass and weeds short;
- Mosquitos struggle to fly in a breeze, so consider installing fans inside the stable;
- Spray a horse-approved mosquito repellent;
- Discourage birds from nesting in or near your stables. If you notice dead birds, be extra- vigilant of your horses’ health.
Finally, remember that a horse in good health has a far better chance of surviving any infection.
Kim Dyson breeds Arabians and Lusitanos, and has 22 years’ experience in holistic equine and human body work.