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Veterinarians warn producers to watch for West Nile Virus, Epizootic Hemorrhagic Disease

by Wyoming Livestock Roundup

As summer begins to wind down, animal health concerns have begun to emerge around the state again. 

As a result, the Wyoming Livestock Board veterinary staff wants to update Wyoming livestock owners about two important disease issues currently in the state. One disease, Epizootic Hemorrhagic Disease (EHD), is clinically very similar to bluetongue, and the other, West Nile Virus, has been found in many areas of the state.

Epizootic Hemorrhagic


Reports of dead and sick deer in northern Big Horn County in the past several months raised concern among livestock producers in the area that another outbreak of bluetongue virus might be imminent.

It was originally believed the deer deaths reported in Big Horn County in late July and early August may have been caused by bluetongue virus. However, recent lab results showed that cause of death was actually EHD.

“There was some earlier speculation that it could have been bluetongue,” says Logan, “but EHD and bluetongue look very similar. Only laboratory virus isolation can determine which it is.”

EHD is also responsible for white-tailed deer and antelope deaths near Sheridan and Wright.

EHD heavily impacts deer, but it can also infect other cervids and antelope.  

“As far as we know, sheep do not exhibit the clinical signs of EHD, but it can be seen in cattle,” Logan explains. “Last year, Nebraska had a severe outbreak, and we had one case in Goshen County.” 

Logan says the symptoms are primarily oral lesions, lameness and profuse salvation. 

“Animals will go off of feed and exhibit fever and depression,” Logan elaborates. “The animal will become dehydrated, and it will rapidly go downhill from there. They become so sore-mouthed that they will not want anything near them.”

Although symptoms can be treated, there is no treatment for EHD itself. 

For prevention, it is best to move them away from standing water and apply an insecticide to the herd.

“It is better to apply the repellant to the animal rather than the area because the vector, Culicodies or no-see-um, move in different directions with wind currents and watersheds,” Logan says. “Direct treatment of the livestock is the best preventative.”

If animals exhibit symptoms, producers should call their local veterinarian and the state veterinarian. 

West Nile Virus

Logan says cases of WNV have been reported in Sheridan, Campbell, Natrona and Laramie counties

“There are six or eight cases of WNV in horses that have been reported around the state, and I expect there are more that have not been reported,” states Logan. “The insect vectors that carry it are out there across the state.”

In protecting against WNV, annual boosters are proven to do the most good, but applying repellant also helps.

“The thing to remember with fly spray is that those things are very short-lived on an animal, and owners cannot rely on just repellant,” Logan explains.

Although an animal may be infected without exhibiting symptoms, owners should watch for clinical signs.

“The symptoms are neurologic,” Logan continues. “The severity is variable from animal to animal, and symptoms are similar to sleeping sickness. The horse will have a fever, depression and may have a droopy lower lip or eyelid. It can progress to the point that the animal goes down and cannot get up.”

“Most of the time, symptoms are mild, and horses can overcome it by themselves, but if signs are visible, it will be seen as neurological,” he adds.

Logan reminds horse owners that reporting WNV cases is required by rule and statute, but affected animals are not quarantined because there is not direct spread from one horse to another. An insect vector transmits the disease to horses and humans.

“There is no way to quarantine mosquitoes,” he explains, “and WNV does not spread from animal to animal.”

Kelsey Tramp is the assistant editor of the Wyoming Livestock Roundup and can be reached at

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