Mosquito-Borne Diseases Pose Threat to S.C. Horses

COLUMBIA — A five-milligram mosquito can slay a 1,000-pound horse in a matter of days. All it needs is the right virus.

But with your help, the horse can survive the attack. All you need is the right vaccine — at the right time.

Now’s the time.

“Last year in South Carolina, we had 10 cases of West Nile Virus in horses and another nine of Eastern Equine Encephalitis (EEE),” said Sean Eastman, director of field services for the Animal Health Programs branch of Clemson University Livestock-Poultry Health.

“These diseases have a very high mortality rate in exposed, unvaccinated horses — between 30 and 40 percent for West Nile and 90 percent for EEE,” Eastman said. “With the emergence of mosquitoes and the appearance of these viruses in nearby states, proper vaccination for horses is essential.”

West Nile and EEE are transmitted to horses by mosquitoes, often the black-tailed mosquito, Culiseta melanura, which is a scourge from Maine to Mexico. Reducing mosquito populations around the farm is a good first step, but only vaccination can prevent the disease from developing once a tiny infected assassin buzzes into the barn.

Livestock-Poultry Health, a regulatory arm of Clemson’s Public Service and Agriculture unit, recommends at least annual vaccinations for both Eastern and Western Equine Encephalitis, West Nile Virus  and rabies in consultation with the owner’s veterinarian. A diagnosis or symptoms suggesting any of these diseases are required to be reported to the state veterinarian’s officewithin 48 hours.

“These diseases can quickly get out of hand if we don’t vaccinate horses,” said Boyd Parr, state veterinarian and Livestock-Poultry Health director. “The best defense is for owners to maintain current equine vaccinations for their horses.”

Although tetanus is not among the required “reportable diseases,” Parr and Eastman highly recommend that horses be vaccinated for tetanus at the same time.

The Palmetto State has made progress in combatting these common equine diseases. In 2013, South Carolina led the nation with 49 cases of EEE in horses, 48 of which died. The numbers have come down gradually, but the state isn’t out of the woods yet.

“When I was a commercial veterinarian I would ask my customers, would you like to pay $40 now or several thousand to treat your horse later and hope the treatment works,” said Eastman, who now directs Livestock-Poultry Health animal health inspectors who routinely visit sale barns across the state. “It honestly may come down to a choice between a dead horse or spending $40 to keep him safe.”

EEE symptoms

Although people are not immune, Eastern Equine Encephalitis is a rare illness in humans, according to the Centers for Disease Control and Prevention (CDC). Most people infected will show no apparent illness, but severe cases begin with the sudden onset of headache, high fever, chills and vomiting. It can be fatal. People who are concerned should contact their physicians, Parr said.

Symptoms in horses usually develop from two to five days after exposure. These include stumbling, circling, head-pressing, depression or apprehension, weakness of legs, partial paralysis, inability to stand, muscle twitching or death.

West Nile symptoms

Most people infected with the West Nile virus, the CDC says, do not show signs of it at all. The rest, about 20 percent, may develop a fever with other symptoms, such as headache, body aches, joint pains, vomiting, diarrhea or rash, but most will recover completely, though weakness and fatigue may linger.

A small number, about 1 in 150, develop a severe illness that affects the central nervous system, such as encephalitis or meningitis. About 10 percent of those will die, according to the CDC.

In horses, West Nile infection often produces flu-like signs, including depression and mild anorexia; occasional drowsiness; skin sensitivity and brief, spontaneous contractions of fine and coarse muscle and skin tissue; changes in mental activity, such as lack of attention; weakness and the loss of control of body movements, such as propulsive walking or pushing forward.

In South Carolina, 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, www.clemson.edu/lph.