Understanding West Nile Virus in Horses

West Nile Virus (WNV) is a disease transmitted to horses via mosquito bites. Not all horses infected with the WNV show overt clinical signs. However, those that do may exhibit several symptoms, including but not limited to:

Flulike symptoms such as mild anorexia and depression

Fine and coarse muscle and skin fasciculations, or involuntary twitching

Hyperesthesia – hypersensitivity to touch and sound

Changes in mental activity where horses appear daydreaming or “just not with it”

Occasional drowsiness

Propulsive walking, which is often uncontrollable

Spinal signs such as asymmetrical weakness and ataxia, which may be asymmetrical or symmetrical

Regrettably, there is currently no cure for WNV, although some horses can recover with supportive care. Mortality rates among equine cases can reach a staggering 30-40%.

Prevention Through Vaccinations and Proper Care

Studies have shown that vaccinations can be a highly effective method of preventing WNV in horses. Horses that have been previously vaccinated require an annual booster shot, although some veterinarians might recommend two shots annually – one in spring and another in the fall – in areas with prolonged mosquito seasons. Horses that have not been previously vaccinated will require a two-shot vaccination series over a three- to six-week period optimizing the immune response.

It should be noted that it does take several weeks for horses to develop adequate protection against WNV after a complete vaccination or administration of a booster.

Mosquito Control

In addition to vaccinations, horse owners should be proactive in implementing measures to reduce mosquito populations and breeding areas and limit horses’ exposure to mosquitoes. These measures can include:

Elimination of stagnant water sources

Regular cleaning and refilling water buckets and troughs

Limiting horses’ outdoor time during peak mosquito feeding times, typically early morning and evening

Applying mosquito repellents approved for equine use

Takeaway

The recent case in South Carolina highlights the importance of WNV vaccinations and mosquito population control in the equine community. Through proactive and responsible horse care, we can reduce the risk of WNV and protect the health and well-being of our equine friends.