The state Veterinarian’s Office has now verified 30 cases of an invariably fatal horse illness transmitted by mosquitoes.
That is twice the amount of cases of Eastern equine encephalitis found in South Carolina horses in 2012, according to Dr. Adam C. Eichelberger. He said Friday that five dead horses in the tri-county area have tested positive for the illness, which is fatal in about one-third of human cases.
The Centers for Disease Control has reported no human cases of the illness in South Carolina for the current year. Eichelberger said Lee County had its first confirmed equine case this past week. Sumter, which now has three confirmed equine cases, was the first county to have a horse test positive this year.
Clarendon County has also had one horse die from the disease, which is maintained in nature through a bird-mosquito cycle, according to the CDC. The mosquitoes that carry the illness — primarily the blacktailed mosquito — feed on the blood of birds. The virus steadily increases throughout the summer as more mosquitoes feed on more birds and propagate the illness.
The mosquitoes then spread the illness from birds to horses, humans, other mammals and even reptiles and amphibians.
“It’s a particularly virulent illness in horses, killing about nine out of 10 horses who get the disease,” Eichelberger said. “Symptoms in horses typically develop between two and five days after exposure and include stumbling, circling, head pressing, depression or apprehension, weakness of legs, partial paralysis, the inability to stand and muscle twitching.”
Fourteen horses died of the disease in 2012, according to state veterinarian Dr. Boyd Parr. No human cases were verified that year. This year, Georgia has confirmed one human case, while Florida has confirmed two.
Symptoms in humans occur within three to 10 days after exposure and include high fever, muscle pain, altered mental status, headache, meningeal irritation, severe sensitivity to light and seizures.
“If anyone has clinical signs where they suspect they may have been exposed to West Nile or EEE, they should contact their human health care provider immediately,” Eichelberger said. “Now that we know that there are mosquitoes in the area that have this disease, our biggest concern is making the public aware that they need to keep themselves and their animals safe.”
According to Eichelberger, one major way tri-county residents can remain safe is by vaccinating horses against EEE and other mosquito-borne infections such as West Nile virus and monitoring mosquito activity near their homes.
“They can greatly reduce the number of mosquitoes by limiting places for standing water, even in as much as one-half inch,” Eichelberger said, noting that mosquitoes can lay eggs in as little as a teaspoon of water.
Sumter County Vector Control Director Alan Penland, who said his trucks are still going out and spraying for mosquitoes each weeknight, added that flower pots, buckets, tarps or anything else that can accumulate water should be checked. Tire swings should have holes drilled in them to allow water to escape.
“Excessive brush on a property can also create an environment for mosquitoes,” Penland said. “Bird baths and pet bowls should also be cleaned regularly to prevent mosquitoes from laying eggs in them.”
Eichelberger reiterated that if one feels he has symptoms of EEE or West Nile virus, he should see his family practitioner.
“We do not make medical diagnoses, nor do we treat humans,” Eichelberger said. “A physician can do the proper testing for these illnesses and make treatment decisions.”