Skip to Content

The Weekly News Source for Wyoming's Ranchers, Farmers and AgriBusiness Community

Equine Infectious Anemia cases in Montana not a cause for worry in Wyoming

by Wyoming Livestock Roundup

Equine Infectious Anemia (EIA), also known as Swamp Fever, is a vector-borne virus affecting horses, mules and donkeys. Flies and bugs carrying EIA transfer the deadly virus by biting horses.

“There are actually a lot of horses that can have the virus, test positive for EIA in blood work and show no symptoms,” says Jim Logan, Wyoming state veterinarian.

Typical symptoms include fever, depression and stocking-up, or fluid retention in the lower legs. Other symptoms are lethargy, anemia, anorexia or loss of appetite and swelling of the legs and lower belly.

“Of the many horses I’ve seen test positive for EIA, only a couple really showed any symptoms, so it’s important to monitor horses,” Logan states.


If a horse contracts EIA, the horse will either die from the disease or be a lifelong carrier of EIA, Logan says.

“The fact that EIA doesn’t have a vaccine or any treatment options makes this disease deadly,” he mentions.

In the United States, horses moving across state lines are required to have a negative Coggins test, which checks for EIA, within the last year. Some states require Coggins tests to be taken within the last six months.

“Since there is no treatment or vaccine, state and federal rules require infected horses to be quarantined indefinitely under strict conditions, or they must be euthanized,” Logan states.

The Wyoming Livestock Board considers EIA a reportable disease. The state veterinary lab or any other lab with positive Coggins tests must notify the state veterinarian.

“Once the state vet is notified of a positive Coggins test, the entire premises and infected animals are quarantined, including any horses within 200 yards of the infected animal. Nearby horses are also quarantined until they are tested and come back with a negative result,” comments Logan.

Known cases

Recently, multiple horses in Gallatin County, Mont., tested positive for EIA. Logan says there are also a couple recent cases in Kansas.

“Producers shouldn’t worry too much about EIA spreading into Wyoming,” assures Logan.

If Wyoming does have a horse infected from the case in Montana, there would be some impacts, but at this stage, it is too early in the epidemiology to tell whether there are any connections, Logan says.

Over the last 10 years, Wyoming has had about four cases of EIA.

When a case of EIA is detected, an epidemiologic workup is performed to figure out where the infected horse comes from, where they have been moved to and if they have had contact with other horses.


For horse owners, two precautions can be taken to prevent EIA.

“People buying horses should have them tested for EIA before putting the new horse in with other horses,” comments Logan.

“The best prevention method is insect control, especially during peak fly season,” he adds.

The most common vectors for EIA are horse and deer flies. Other insects are potential carriers, but typically little bugs, like mosquitoes, aren’t an issue, says Logan.


Unless there is a connection with the case in Montana, Wyoming won’t know exactly where the EIA infection is or the identity of the ranch where horses are infected because of confidentiality statutes across the country, according to Logan.

“My advice would be to practice good insect and tick control. Also, owners should be vigilant when it comes to watching for symptoms of EIA,” Logan states.

Horses not traveling across state lines aren’t required to be tested for EIA.

“I don’t think horses that stay on the ranch need to be tested for EIA regularly. Owners do need to be aware of EIA symptoms and have horses tested if they show any signs of EIA,” Logan says.

Heather Loraas is assistant editor of the Wyoming Livestock Roundup and can be reached at

  • Posted in Animal Health
  • Comments Off on Equine Infectious Anemia cases in Montana not a cause for worry in Wyoming
Back to top