Dr. Lew Strickland, University of Tennessee Extension veterinarian, and Dr. Jennie Ivey, University of Tennessee equine Extension specialist, encourage Tennessee equine owners to be proactive in preventing WNV from affecting their horses.
“WNV is the leading cause of encephalitis in horses in the United States. This virus is present in all of the continental United States, along with most of Canada and Mexico,” Strickland said. “It is important for owners to be educated on transmission, vaccination and management strategies.”
Transmission of the virus happens from bird reservoir hosts by mosquitoes to horses. This means a mosquito must feed from an infected bird, then it can transmit the virus to a horse or human during another blood meal. Horses and humans are dead-end hosts for WNV, meaning the virus is not directly contagious from horse to horse, or from horse to humans. The case fatality rate for horses exhibiting clinical signs of WNV infection is about 33 percent and horses that survive the acute illness caused by WNV have the potential to exhibit residual effects up to six months post-diagnosis.
Affected horses may be depressed and off-feed. Horses with WNV often have muscle tremors and may have convulsions. Some affected horses experience hypersensitivity and maybe easily startled by noise or touch, while others seem drowsy and less reactive than normal. Other signs include walking continuously without purpose or control, circling, exhibiting lack of coordination, and experiencing paralysis, especially in the hind legs.
Most veterinarians currently recommend that horses in Tennessee receive spring and fall booster vaccinations after the initial two-dose vaccine series. This procedure enables horses to maintain a high level of antibodies against WNV. It is extremely important that horses initially receive two doses of the WNV vaccine at the time interval recommended by the vaccine manufacturer. Maximal protection does not occur until several weeks after the second, initial vaccination Due to its prevalence, the American Association of Equine Practitioners considers the WNV a core vaccine, and recommends vaccination for all horses in North America independent of location, travel and management practices.
Vaccination alone may not give your horse full protection, and a variety of management strategies can be helpful in disease prevention. Mild winters and plentiful rain in the Southeast create ideal conditions for WNV to become a year-round problem with more intense outbreaks in the summer and fall due to mosquito population. Since mosquitoes are the vector for WNV, insect control is key in prevention of this disease.
Ivey said, “Mosquitoes require stagnant water to reproduce. Inspect areas around your barn for potential sources of standing water and take action to remove if possible.”
Any object that can hold water can become a breeding ground, including buckets, old tires, puddles or flooded pastures and unused water troughs. Create drainage for areas that tend to collect water after rain showers. Bring horses inside during peak insect feeding times early morning and dusk. In addition, topical insect control applied to your horse will repel mosquitoes feeding.
WNV can certainly be a devastating disease for your horse; however, a prevention protocol will reduce the risk of this disease on your farm.
For more information, contact the UT-TSU Extension Office in Wilson County at 615-444-9584. You can also find us on Facebook or visit extension.tennessee.edu/wilson. Ruth Correll, UT Extension-TSU Cooperative Extension agent in Wilson County, may be reached at 615-444-9584 or email@example.com.