An outbreak of herpes was caught at an Ocala, Fla. horse show in late February, and the University of Georgia's College of Veterinary Medicine is helping get to the bottom of it.
At the show, one of the contestants showed “clinical neurological signs on February 20, 2013,” according to a Georgia Department of Agriculture press release.
The College of Veterinary Medicine ran diagnostic tests on samples from the horses exposed in the outbreak.
Known as Equine Herpes Virus (EHV-1), the infection differs greatly from its human counterpart. Aside from both being transmitted sexually, EHV-1 can be transmitted by contact and through the air.
“It is distinct and only infects horses,” said Jeremiah Saliki, professor and head of the virology and serology sections in the College of Veterinary Medicine. “It can be transmitted by aerosols, which means if a horse sneezes around another horse, it can be transmitted. Then, it could be transmitted by direct contact from horses touching each other...and can be sexually transmitted. The main route of transmission is by aerosols.”
Owners are recommended to have their horses “isolated when returned home and observed closely for the next 21 days,” for horses that went to the event and not quarantined, according to the press release.
The origin of the outbreak is still unknown.
“My understanding is they do not have an understanding of the origin of the virus,” said Robert Cobb, division director of animal industry and state veterinarian for the Georgia Department of Agriculture.
The virus has numerous strains, and victims of EHV-1 are subject to worsening conditions that could affect the lungs, brain, nervous system and the foal of the horse — depending on the strain.
“There are three conditions that equine herpes virus causes,” Saliki said. “There’s respiratory disease, encephalitis and abortion. But not all strains of the virus cause of all of those three. There are some strains known to be neural-pathogenic, which means it causes diseases in the nervous system. So some strains cause only respiratory disease and abortion, and some will cause only neurological disease, and some can cause all three.”
Encephalitis is an inflammation of the brain most commonly as a result of a viral infection. Many symptoms of encephalitis appear flu-like, but seizures and problems with movement can also follow.
The UGA College of Veterinary Medicine has been conducting tests in response to the outbreak. But EHV-1’s clinical signs make it difficult to distinguish from the equine influenza.
“There is no way you can — by just looking at clinical signs — differentiate between the equine flu and equine herpes,” Saliki said. “They can cause clinical signs that are identical, and that is why laboratory testing is necessary.”
Saliki said that to correctly diagnose the horses, four lab technicians, under his supervision, tested exactly 219 horses for EHV-1. The tests were done on nasal swabs and blood samples from each horse.
“We have done some work, but it concerns only diagnostic testing [through] samples submitted from the outbreak in Florida,” he said. “In fact, just last week, we tested over 200 horses from Florida from that particular outbreak.”
Of all the horses tested by the four technicians, none tested positive for viral infection.
But there have still been reports of EHV-1 within Georgia.
“We have had eight different animals [in Georgia] test positive for EHV-1,” Cobb said. “That means these animals have been exposed to it in the past, or they have been vaccinated.”
These positive tests do not guarantee the animals are “currently sick,” Cobb said. More so, he said a link between the horses with EHV-1 in Georgia and the outbreak in Florida does not exist.
He explained the prevalence of the virus is the reason for the cases in Georgia.
“The positive horses that are reported within Georgia have had no connection to Florida,” Cobb said. “All the animals we knew during the outbreak there...we have visited their premises to determine if they did have illness, and we have not found any illness in them.”
While there is “no specific cure,” Saliki said treatment using anti-inflammatory drugs and antibiotics effectively relieves symptoms. Saliki also said a vaccine is out on the market.
“For prevention,” Saliki said, “there is a vaccine, but once the animal is clinically sick, the vaccine has no effect. It only has an effect in preventing the animal in getting infected.”
But the vaccine does not protect against all symptoms of EHV-1.
“The vaccine does not from protect the neurologic form,” Cobb said. “The vaccine can be used prior to exposure and can hopefully prevent some of the symptoms — such as abortion and respiratory disease. But it is not recommended to be used after exposure. It has been documented that it can actually increase the instance of neurologic disease from herpes.”
Fortunately, the Florida outbreak has begun to lose its momentum.
“As far as in Florida, they have released the quarantines,” Cobb said. “I’m not sure if they all have been released, but the original one has been released, and to my knowledge there have not been any more positive cases.”