State by State: Equine Herpes Virus Around the USA This Week

Quarantines, Deaths, and Cases in Treatment for EHV
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Quarantines, Deaths, and Cases in Treatment for EHV
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Has your state been affected by a biosecurity alert related to equine herpes virus (EHV) this year? It’s been an active spring for the virus, which has shown up from coast to coast and affected horses and their owners in minor and major ways. In some states, events were cancelled, but no matter where you go, horse owners are concerned about going to shows and sales and trail rides where they will come into contact with a large number of horses.

But you don't have to live in a state with active EHV to be affected, or even leave your own farm. Of even more concern to many owners is the return of horses from shows and events. We are face to face with the dizzying reality of the level of motion of horses in the United States. Owners trailer their horses to clinics, lessons, vet treatments, farrier appointments and even just to ride in a ring. Avoiding contact with other horses is almost impossible.

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Can disease prevention be achieved if our horses don't stand still?

This week’s states-to-watch are Oregon, Illinois and Iowa. Here’s an update on the situation in each from each state’s latest official update.


There were no additional cases of horses infected with Equine Herpes Virus (EHV-1) last week, according to State Veterinarian Brad LeaMaster of the Oregon Department of Agriculture in a report issued on May 14th. Over the previous two weeks, nine horses had either developed neurological signs of the infection or had developed fevers with no neurological signs after being exposed to EHV-1. All horses involved remain under active observation by owners and their veterinarians. Eight farms remain under quarantine, six in Marion County and two in Polk County.

There have been no deaths associated with the EHV-1 outbreak in Oregon so far. Two horses that were hospitalized at Oregon State University College of Veterinary Medicine’s Large Animal Hospital have responded to treatment and have been sent home.

“The fact that there have been no new reports of the virus in Oregon is encouraging news and may indicate that the outbreak situation has stabilized,” said LeaMaster.

All affected horses have been linked to an Oregon High School Equestrian Team (OHSET) meet at the Linn County Fairgrounds on April 16-19.

“I am aware that many equine shows and other events have been cancelled or postponed this past week,” said Brad LeaMaster. “It is a very tough decision to make, however, I commend those event organizers who made that call as well as the many horse owners who decided to just stay home. That was a responsible thing to do and I feel that those actions have been the key reason for no new infections being reported this past week.”


The Iowa Department of Agriculture and Land Stewardship announced on May 13 that a horse stable in Warren County, Iowa has had several confirmed cases of Equine Herpesvirus Myeloencephalopathy (EHM).

All horses at the facility are being monitored for the disease and are not permitted to leave the site.


On Friday May 8, the Illinois Bureau of Animal Health and Welfare was notified that two horses located in a stable in northeast Illinois tested positive for EHV-1 via the nasal swab PCR test. Additional horses at the same stable had exhibited fevers throughout the week of May 4. Three horses have exhibited neurologic signs of disease and two of those horses have been euthanized.

All horses on the premises have been restricted to the stable and are being monitored daily for signs of disease. Stable personnel have been instructed to eliminate direct contact between horses as much as possible and to segregate sick horses from healthy horses as well as limit personnel entering the barn.

The stable manager has implemented enhanced cleaning and disinfection measures to help decrease the possibility of exposure. A source of the initial exposure has not been identified.

It was also reported to the Bureau that several horses from this stable attended equine events on or about April 25th and on May 2nd. These venues have been contacted and are implementing steps to reduce the chances of additional exposures.


After this article was published, the state government in Pennsylvania announced an equine herpes virus alert for that state. The Pennsylvania Department of Agriculture notice details the quarantine of an equine barn in Tionesta (Forest County), after a horse at the barn tested positive for Equine Herpesvirus Type 1 (EHV-1) on Wednesday, May 13.

The announcement also states:

"A horse from the barn was used in the Tionesta Wounded Warrior Horseback Scavenger Hunt, where 94 horses took part, including horses from Ohio and West Virginia.

"An equine barn in Shippenville (Clarion County), housing an exposed horse that showed clinical signs of EHV-1 was put under precautionary quarantine on Thursday, May 14, until the pending laboratory results are confirmed. 

"Two additional horses from the Forest County equine barn have shown signs of illness after being exposed to the positive horse.

"The Pennsylvania Department of Agriculture is in the process of tracing the horses that participated in the scavenger hunt, and has notified animal health officials in Ohio and West Virginia."

Just part of the picture

And it’s not just EHV...We are just beginning to enter the insect-borne disease season, and there have also been reports of rabies affecting horses around the country. Ticks are heavy in the grass this time of year, and both horses and humans are at risk for Lyme disease in many states.

More seriously, Vesicular Stomatitis (VS) continues to be a problem in Arizona and Utah. The disease was especially dangerous to horses in Colorado and Texas last year: what will this year bring?