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Animal health authorities fight back against equine virus


COLUMBIA — While South Carolinians have battled COVID, the state’s horses have fought viral diseases of their own. A sudden spike in cases of Eastern Equine Encephalitis (EEE) in 2020 — 17 cases compared to the five cases reported in 2019 — has animal health authorities poised to fight back against viral disease threats.

“We’d like to see our numbers reduced to zero in 2021,” said Michael Neault, South Carolina state veterinarian and director of Clemson University Livestock Poultry Health, a state agency responsible for protecting the health of animals and consumers through control of disease and inspection of meat and poultry products.

Effective vaccines exist for both EEE and West Nile Virus, which are viral diseases that attack horses and other equine hosts through the nervous system. Borne by mosquitoes, EEE is almost always fatal in unvaccinated horses.

“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,” said Sean Eastman, veterinarian and director of field services for the Livestock Poultry Health Animal Health Programs. “With the emergence of mosquitoes continued vaccination for horses is essential.”

Success in South Carolina through the years proves that point. The Palmetto State led the nation in cases of the disease in 2013 with 49 EEE infected horses, all unvaccinated. Of those, 48 died. Over the next five years, the number of confirmed cases of EEE decreased steadily until rising in 2019 and 2020. Cases of West Nile Virus have decreased over the past four years from 10 confirmed cases in 2017 to one case in 2019 and again in 2020.

“Since the 2013 case number peak, our office has stepped up efforts in cooperation with equine practitioners in South Carolina to increase awareness among horse owners of the risks associated with not vaccinating,” Neault said. “Last year, with the economy being affected by the COVID-19 pandemic, we think vaccination rates were down and that likely is a significant factor in the increase of cases in 2020.”

Other deadly diseases, including rabies, are a danger to equine livestock without vaccinations.

“Horse owners should check with their veterinarian to be sure their horses’ vaccinations are up to date,” Neault said. “This is the time of year that these diseases may begin to appear. The best defense is to maintain current equine vaccinations for Eastern Equine Encephalitis, West Nile Virus and also rabies for your horses.”

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. Due to the warm, wet winter South Carolina experienced this past year, mosquitoes have been active all winter and the forecast for the summer is that more than a normal number of mosquitoes will be active.

Two to three days after becoming infected with the virus, a mosquito becomes capable of transmitting the virus. Infected mosquitoes can transmit the disease when they bite. Symptoms usually develop in horses from two to five days after exposure.

Any livestock, including horses, that display neurologic signs, such as 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.

Information on animal diseases and reporting requirements can be found on the Livestock Poultry Health website,

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