With recent rain and humid conditions creating favorable environments for mosquitoes, Clemson University Livestock-Poultry Health is reminding horse owners to make sure their animals are vaccinated against eastern equine encephalitis (EEE) and West Nile virus (WNV).
No equine cases of EEE or WNV have been reported in South Carolina this year. However, mosquito-borne disease activity nationally and recent West Nile virus activity in South Carolina highlight the importance of remaining vigilant.
The South Carolina Department of Public Health recently announced a West Nile virus outbreak in the Pee Dee after two people were diagnosed within a similar time frame and geographic area. DPH also reported 10 EEE-positive horses in South Carolina during 2025.
“Not having a recent confirmed case in livestock does not mean there is no risk. Vaccination is the best way horse owners can protect their animals from these serious diseases, and it should be part of every horse’s routine preventative health plan.”
Catherine Harris, Deputy State Veterinarian and Director of Animal Health Programs at Clemson Livestock-Poultry Health
EEE and WNV are transmitted by mosquitoes that become infected after feeding on birds. Horses and humans can become infected through the bite of an infected mosquito, but neither disease is spread from horse to horse or from horses to people.
Both diseases can cause neurologic illness in horses. Signs may include fever, depression, incoordination, weakness, muscle tremors, changes in behavior, difficulty swallowing, head pressing, seizures or inability to stand. Owners should contact a veterinarian immediately if a horse shows signs of neurologic disease.
Horse owners should:
- Ask their veterinarian whether their horses are current on EEE and WNV vaccinations and whether boosters are recommended based on local conditions, travel or other risk factors.
- Eliminate standing water where mosquitoes can breed, including water in buckets, tires, gutters, troughs and other containers.
- Keep horses indoors during periods of peak mosquito activity, particularly from dusk to dawn, when practical.
- Use fans in stalls and apply only equine-approved mosquito repellents according to label directions.
- Monitor horses closely for signs of illness and contact a veterinarian promptly with concerns.
The American Association of Equine Practitioners considers EEE and WNV core vaccinations for horses. Vaccination schedules can vary, so owners should consult their veterinarians to determine the appropriate timing and frequency for their animals.
“Vaccination and mosquito control work together,” Harris said. “Even when disease has not been detected in a particular area, conditions can change quickly as mosquito populations increase.” For more information about equine diseases, visit Clemson Livestock-Poultry Health at clemson.edu/public/lph.
