West Nile Virus is one of those issues that almost any horse owner hears about and shudders. It is a customary practice for horses to be vaccinated against this disease, but in the past couple of years, West Nile Virus (WNV) has not been talked about nearly as much in the equine world. Is it still a concern?
West Nile encephalitis describes an inflammation of the central nervous system, which is caused by infection with West Nile Virus. In horses that do become clinically ill, the virus infects the central nervous system and may cause symptoms of encephalitis.
Clinical signs of encephalitis in horses may include a general loss of appetite and depression, in addition to any combination of the following signs: fever, weakness or paralysis of hind limbs, impaired vision, general weakness, head pressing, wandering, convulsions, inability to swallow, walking in circles, hyperexcitability and coma.
If you notice your horse displaying any of these symptoms, contact your veterinarian immediately. Treatment for West Nile Virus may differ depending on your region.
“While most horses that recover from West Nile Virus have a full recovery, about 40 percent have some long-term effects,” said Marci Crosby, University of Missouri-Extension Equine Program Coordinator at the University of Missouri.
She also noted that this disease is fatal in one-third of all cases.
A concern for some horse owners is not just whether to vaccinate against the disease, but how to go about protecting pregnant mares and foals from the disease.
According to American Association of Equine Practitioners, limited studies have been performed that examine protection through vaccination against WNV disease in pregnant mares. While none of the licensed vaccines are specifically labeled for administration to pregnant mares at this time, practitioners have vaccinated pregnant mares due to the risk of natural infection. It is an accepted practice by many veterinarians to administer WNV vaccines to pregnant mares as the risk of adverse consequences of WNV infection outweighs any reported adverse effects of use of vaccine.
For foals, the first dose of the vaccination can be administered at 3 to 6 months of age for the offspring of unprotected mares, and 4 to 6 months of age for offspring of protected mares.
The bottom line for dealing with West Nile Virus today is that prevention is better than the cure, and while the disease isn’t rampant in the Ozarks, there is no reason to not protect your equine friend and working partner.
“The vaccine is effective and safe, and helps to safe guard horses from the severe form of the disease,” Crosby said. There are also management practices to decrease the risk of your horse receiving a bite from an infected mosquito that can be implemented on your farm or in your facility.
“West Nile is only spread through mosquito bites, so anything that decreases mosquito habitat (standing water) and decreases a horse’s exposure to mosquitos (sprays, fans, etc.) can be beneficial. Most fly repellents work for only short amounts of time, so owners can get the most benefit by removing all standing water around their barns, or using mosquito dunks in standing water,” Crosby advised.


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