Eastern Equine Encephalitis Outbreak in SC: Horses Lost, Prevention Tips

Understanding Eastern Equine Encephalitis (EEE)

State officials in South Carolina have confirmed the deaths of two horses due to Eastern equine encephalitis (EEE), marking the first cases of the 2025 season. The affected animals include a five-year-old unvaccinated stallion in Jasper County and a five-year-old mare in Aiken County, whose vaccination status is still under investigation. These cases were confirmed by the National Veterinary Laboratories on July 24, according to Clemson University's Department of Livestock Poultry Health.

EEE is a viral disease transmitted through mosquito bites, which can cause inflammation of the brain, known as encephalitis. While rare, the virus is considered one of the most severe arboviral encephalitis affecting the United States. According to the National Library of Medicine, EEE is an emerging disease with a rising incidence rate. Annually, between six and eight cases are reported, typically between May and October. Most cases occur in Florida, Georgia, Maryland, Wisconsin, and New Jersey.

The virus has a high fatality rate, with approximately 30% of infected individuals dying from the disease. Survivors often experience long-term neurological issues. In horses, the mortality rate for EEE is particularly alarming, reaching up to 90% in unvaccinated animals. This underscores the importance of vaccination as a critical preventive measure.

Protecting Horses from EEE

South Carolina state veterinarian Michael Neault emphasized the need for horse owners to stay vigilant about vaccinations, especially during the summer months when conditions favor mosquito proliferation. "We've had a lot of rain and warm temperatures, leading to high mosquito populations," Neault said. "It's crucial for horse owners to keep up with their vaccination schedules, especially during these times."

Neault also recommends that horse owners ensure their animals are up to date on West Nile virus and rabies vaccinations. These diseases, like EEE, are transmitted by mosquitoes and pose significant health risks to both animals and humans.

Human Risk and Symptoms

Humans can contract EEE from the bite of an infected mosquito, according to the Centers for Disease Control and Prevention (CDC). Approximately 30% of those infected develop severe symptoms and may die. Survivors often face ongoing neurological complications. Currently, there are no vaccines or medications available to prevent EEE in humans, making prevention through mosquito bite avoidance essential.

Common symptoms of EEE in humans include fever, headache, vomiting, diarrhea, seizures, behavioral changes, and drowsiness. Early recognition of these signs is crucial for prompt medical intervention.

Recognizing EEE in Horses

In horses, EEE symptoms usually appear within two to five days after exposure. These symptoms may include stumbling or incoordination, circling or head pressing, depression or apprehension, weakness or partial paralysis, muscle twitching, inability to stand, and sudden death. Horse owners should be attentive to any unusual behavior or physical changes in their animals.

Preventing Mosquito Exposure

Reducing mosquito exposure is key to preventing EEE in both horses and humans. Effective strategies include eliminating standing water around barns and paddocks, using equine-safe repellents, stabling horses during peak mosquito hours (dusk to dawn), and installing and maintaining screens in stables.

Reporting EEE Cases

South Carolina law requires all suspected cases of EEE, West Nile virus, rabies, or equine herpesvirus (EHV-1) to be reported to the state's veterinarian office within 48 hours. Prompt reporting helps track the spread of the disease and implement necessary control measures.

By understanding the risks associated with EEE and taking proactive steps to protect horses and humans, communities can better manage this serious health threat. Vaccination, mosquito control, and early detection remain the most effective tools in the fight against EEE.