S.D. horse tests positive for EHV-1
May 16, 2014
A horse in Brown County, S.D., which is in the north-central part of the state, has been diagnosed with the "wild," or non-neuropathic, strain of equine herpesvirus (EHV-1), said Dr. Dustin Oedekoven, South Dakota state veterinarian. The horse had recently traveled from Minnesota to a boarding facility in Brown County. The horse does not normally travel to competitions and events, but horses that are boarded near it do, said Oedekoven. "My staff is working with the veterinarian there, the facility owner and the horse owner to make sure appropriate steps are taken to limit the spread of the virus," he said.
What is EHV-1?
EHV-1 manifests with respiratory symptoms, such as a cough and nasal discharge, or neurologic symptoms, such as lack of coordination, inability to stand, urine dribbling and loss of tail tone. EHV-1 may also cause abortion in brood mares.
Respiratory symptoms, sometimes referred to as rhinopneumonitis, are much more common and treatable, and occur most often in young horses that have been under stress, as that caused by weaning.
The neurologic symptoms can be caused by either a mutation of the wild EHV-1 virus, or by the neuropathic EHV-1 virus. The neurologic symptoms resulting from the mutation of the wild EHV-1 virus are called equine herpesvirus myeloencephalopathy, or EHM. The neuropathic strain of EHV-1 is much rarer and more aggressive, with a higher mortality rate. The horse in Brown County, and all the other reported cases of EHV-1 exhibiting neurologic symptoms so far in 2014 have been the result of EHM, not the neuropathic strain of EHV-1.
The symptoms of EHM can be treated, but occasionally the most humane choice is euthanasia, Oedekoven said.
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Oedekoven said researchers are working on figuring out why the wild virus mutates, but they haven't reached a conclusion.
In recent years there has been an increase in EHM cases, leading the Animal Plant Health Inspection Service to consider classifying it as an emerging disease. A disease is considered to be "emerging" when "A disease changes in severity, type of animal that can be infected, or other changes in pathogen behavior." The recent EHV-1 outbreaks seem to be associated with a change in the severity and behavior of the virus, according to the APHIS document. "It does seem to be an emerging disease," Oedekoven said. "A lot of people travel with their horses to multiple weekend events, giving the virus plenty of opportunities to be spread within the horse population. In addition we are seeing more tests available, and more samples collected for testing. These are some of the factors that may be responsible for the increased incidence of EHV-1 cases."
How does it spread?
"The wild type of the virus is very common among the horse population, but often doesn't cause symptoms until the horse has been under the stress of transportation, competition or just being around other horses," Oedekoven said. The stress suppresses the immune system, so the virus can take hold.
EHV-1 is spread by direct or indirect contact with nasal secretions, so any tack, equipment, facility or person who has come into contact with an infected horse can pass the virus on.
Some horses that have the virus pass it on before exhibiting any symptoms, and some horses can pass the virus on without ever exhibiting symptoms, Oedekoven said. According to a document provided by APHIS, most horses have been exposed to the virus by the time they are 2 years old, and foals are often infected by their dams.
"This time of year there are horse events going on every weekend. It's one of those viruses that's easily spread and takes advantage of that type of movement, so is common among horses that are moved a lot. They all share their germs, just like kids that go to kindergarten."
How is it treated?
"The earlier EHV-1 is caught, the better the chance for recovery," Oedekoven said. Whether the horse is showing neurologic or respiratory symptoms, the only treatment is for the symptoms themselves. The owner may not know the horse has EHV-1 with respiratory symptoms because the symptoms go away on their own and never warrant testing.
Horses with neurologic symptoms receive anti-inflammatories to reduce the swelling of the brain and spinal cord. Pressure sores can become an issue on horses that are unable to stand. "The recovery process can be long and the success may depend on the amount of time, effort and care the owner and veterinarian can provide," Oedekoven said.
How can you prevent it?
A vaccine is available that helps prevent the respiratory symptoms and abortion, as well as reducing the likelihood of passing the virus on, but is ineffective against EHM and the neuropathic strain of EHV-1.
"One other problem with the vaccine is that it has a fairly small window of effectiveness," Oedekoven said. "It should be used about three weeks before you anticipate your horse being stressed or exposed to other horses, and boostered every 90 days while there is a chance of exposure. People with brood mares are vaccinating them at five, seven and nine months of gestation."
Oedekoven recommends never sharing buckets, brushes or tack, and regularly cleaning and disinfecting trailers and anything else that may serve to harbor the virus.
Oedekoven also recommends isolating horses that have been co-mingled with other horses for 28 days before allowing them to be around horses that remained at home. "Otherwise you may be exposing the horses back home to the same diseases that the horse that traveled was exposed to," he said.
In many states, EHV-1 is not a reportable disease, which means even if cases are identified, that information does not have to be made public. However, EHM is reportable in South Dakota, and the Minnesota Board of Animal Health voted April 16 to make EHM a reportable disease in that state.
Oedekoven encourages horse owners and event organizers to be aware of what's going on in the industry and to take whatever precautions are necessary to prevent the spread of not just EHV-1, but other contagious diseases as well.
Oedekoven said the cases of EHV-1 that have been reported in surrounding states have centered mostly around barrel races, so that segment of the equine population is being extra careful.
Oedekoven said it's up to the event organizers as to the extent of precautions they want to take. Some events have been cancelled, others are implementing more stringent health requirements. "One thing they can do is strictly adhere to the state requirement to have a current health certificate," Oedekoven said. "The health certificates themselves may not be a guarantee of health, but it means the owner has to be in contact with a veterinarian who will be aware of current health issues." A health certificate is valid for 30 days, but if the owner notices any signs of illness they should contact their veterinarian promptly and voluntarily quarantine their horse until they can obtain a clean bill of health. Health certificates are required at all public exhibitions of livestock, including horses, in South Dakota.
Requiring a temperature reading for each horse at the event every day is another way to minimize the chance of spreading the disease, since fever is one of the early indications of EHV-1.
Oedekoven said all horse owners, whether they are traveling and competing or not, should be aware of the situation and talk to their veterinarian about appropriate vaccinations and prevention practices for their horses. Even horses at brandings and community events have the potential to be exposed to the virus.