Public Service and Agriculture

State veterinarian urges owners to vaccinate their horses against mosquito-borne diseases


Mosquitoes, like afternoon thunderstorms and homemade ice cream, are a feature of summers in the Palmetto State.

So are the diseases mosquitoes can carry and spread.

That’s why State Veterinarian Michael J. Neault is urging South Carolina horse owners to work with their veterinarian to create an appropriate vaccination schedule to protect their animals from Eastern Equine Encephalitis (EEE), West Nile virus (WNV) and rabies.

“So far this year we have had only one case of EEE back in January. That’s quite early, and while it’s not necessarily a harbinger of things to come, it’s time for owners to get their horses vaccinated so we can keep the numbers as low as possible,” Neault said.

Borne by mosquitoes, these diseases have a very high mortality rate in infected, unvaccinated horses — between 30 and 40 percent for West Nile and 90 percent for EEE. However, widespread vaccination has kept the number of cases comparatively low in South Carolina compared to nearby states.

Likewise, mosquito control is an important precaution. Both EEE and West Nile Virus are maintained in nature through a cycle involving the freshwater swamp mosquito, Culiseta melanura, commonly known as the black-tailed mosquito.

The EEE and WNV viruses are mosquito-borne and fast-acting. Symptoms of EEE in horses usually develop from two to five days after exposure. The symptoms include stumbling, circling, head pressing, depression or apprehension, weakness of legs, partial paralysis, the inability to stand, muscle twitching or death.

In addition to EEE and WNV, other neurologic diseases, including rabies and EHV-1, can infect horses. Any livestock that display neurologic symptoms — stumbling, circling, head pressing, depression or apprehension — must be reported to the state veterinarian at 803-788-2260 within 48 hours, according to state law.

A list of reportable diseases, along with other resources, is published on the LPH website at

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