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EHV-1 pops up in Midwest, reminds horse owners to be vigilant in prevention

by Wyoming Livestock Roundup

From March 14-17, five confirmed cases and two pending cases of equine herpesvirus (EHV-1) were found in eastern Minnesota and western Wisconsin. 

The confirmed cases of herpes were of the non-neuropathogenic form. However, the horses were displaying neurologic symptoms. 

Diagnostic tests on the pending cases have not yet confirmed whether or not they are the neurologic form of equine herpes virus myeloencephalopathy (EHM).

Forms of EHV-1

“The form of EHV-1 being seen in Minnesota can actually cause essentially three different syndromes,” explains Wyoming State Veterinarian Jim Logan. “The respiratory form, which is usually a fairly short duration and relatively mild respiratory infection, may not normally be recognized by owners. When their horse has it because it can be very subtle.” 

Logan continues that the second syndrome of EHV-1 causes abortions in pregnant mares late term. 

The last syndrome of EHV-1 can affect the nervous system, with the animals displaying neurologic symptoms. 


“The neurologic form is more lethal because it can kill horses or permanently paralyze and neurologically affect them, so they have to be put to sleep,” explains Logan. “A lot of horses that contract the neurologic syndrome do survive and recover completely over time.”

The neurologic syndrome of EHV-1 can develop into the EHM form of herpes and is a reportable disease to the USDA, while the EHV-1 form of equine herpes is not a reportable disease. 

However, the Minnesota Board of Animal Health is keeping tabs on all cases and forms of equine herpes virus. 

“Vaccines are usually very good at protecting against the respiratory form and the abortion syndrome of equine herpes, but the vaccine is not so good protecting against the neurologic syndrome, typically,” comments Logan. 

Clinical signs

“Just because a horse is vaccinated, people shouldn’t be too over confident that the animal isn’t going to be exposed and have a problem,” explains Logan. “The other thing people can do is to very closely observe their horses, and it would be a good idea to check their horses daily to see if there is a rise in their temperature.”

If a horse’s temperature rises to 102 degrees Fahrenheit or above, the owner should contact their veterinarian. 

The incubation period for equine herpes virus is typically three to 14 days, but sometimes it may take longer for clinical signs to show. 

“When we have cases of equine herpes, we recommend that horses remain isolated for a minimum of 21 days,” instructs Logan. “Generally, when they are incubating they are not so much contagious. It’s when they break with the disease that they will be more likely to be contagious. However, viral shed can occur at any time after an animal is exposed.”

“There is a possibility that the virus could be shed from an incubating animal, as well,” adds Logan. 

If an owner is suspicious of their horse having EHV-1, symptoms and signs to look for are lethargy, going off feed, fatigue and dribbling urine. 

If the animal becomes neurologic they may begin dragging a leg, getting down and being unable to rise, being wobbly or having an abnormal gait.

Treatment for infected horses is primarily going to be supportive therapy with fluids and non-steroidal anti-inflammatories to keep the brain and spinal inflammation down. 

Also, supplemental nutrition may be given to make sure the animal remains hydrated and receives all the nutrition they need. 

“Horses can be carriers of the disease when they are infected, and they are infected for life,” explains Paul Anderson of the Minnesota Board of Animal Helath. “Usually when horses recover from herpes they don’t shed the virus, but some of these horses can start shedding the herpes virus later in life.”


Anderson went on to explain that EHV-1 survives better in the spring when it’s about 30 degrees Fahrenheit, cloudy and wet and when horses are in close proximity to each other. 

In these conditions, they are more susceptible to contracting the virus. 

“This is not an unusual virus to have in horses this time of year,” comments Anderson. “It certainly is the time of year, during the spring and fall, when they get sick with EHV-1. It’s kind of like the flu in kids.”

“The sunlight kills these viruses pretty readily, so in the heat of the summer when things dry out really quickly, the virus doesn’t survive very well,” describes Anderson. “The equine herpes virus is very fragile, and it really doesn’t like to live outside the horse.”

“We’re certainly talking to our equine folks, and we are recommending if they are  considering whether to go to an event or not that they contact their veterinarian and talk it over,” says Anderson. 

Madeline Robinson is editor of the Wyoming Livestock Roundup and can be reached at

EHV-1 in Wyoming

Wyoming’s State Veterinarian Jim Logan explains there are currently no signs of equine herpes virus neurologic disease in Wyoming. However, there is always some risk of equine herpes entering into the state due to the frequent travel of horses from state to state. 

“There is always a risk of an owner’s horse being at a place where there could be exposure to equine herpes,” says Logan. “When horses come into Wyoming, they have to have a health certificate, which should mean a veterinarian has looked at them and they are not showing any signs of contagious or infectious disease.”

“Certainly, it’s possible that an animal could be incubating an illness and not be showing anything,” adds Logan. 

Preventative measures that can be taken to reduce the risk of horses contracting equine herpes are vaccination and to avoid places where there is a high concentration of horses, advises Logan. Events such as rodeos, ropings and barrel racing should be viewed as potential exposure risks.  

Also, horse owners should not share tack, troughs and water or feed buckets with other horses. 

Logan further advises horse owners to avoid having their horse from having any nose-to-nose contact with other horses. 

“It’s a difficult thing to treat because there is no real magic drug that can be given that will kill the virus,” describes Logan. “What has to be done when treating an animal with equine herpes is to give them supportive therapy of fluids and non-steroidal anti-inflammatories, so their body can respond, and their immune system can fight it off.”

Midwest cases

Paul Anderson oversees the equine program for the Minnesota Board of Animal Health, and he says, “There is no connection between any of the confirmed and suspect horses of EHV-1.”

“The equine herpes virus is a virus that is around throughout the U.S., and it’s around most of the time,” adds Anderson “It is, however, strange to have seven cases of equine herpes all at the same time.”

Two of the confirmed positive horses were from the same premise in Chisago County in Minnesota. One of these horses was euthanized, and the other animal is making a full recovery. 

A horse from Dakota County, Minnesota also tested positive for EVH-1 and was euthanatized, as well. 

The other two confirmed positive cases of EHV-1 are in recovery from the illness and are from Freeborn and Hennepin Counties in Minnesota.

As of March 26, diagnostic tests were pending for the two suspect cases of EHV-1, both from Wisconsin. One of the horses was from Burnett County and was euthanized. The other horse is beginning to recover and is from Polk County. 


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