Bighorn sheep and mountain sheep share respiratory pathogens, research team finds

A team of researchers from the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) has discovered that bighorn sheep, a member of the sheep and goat family, can pick up and spread many of the same respiratory pathogens that can affect bighorn sheep, a Texas native that often shares habitat with bighorn sheep.

The research, published in the journal PLOS ONEwill help wildlife advocates better understand the complex relationship between these two species and promote management of both species.

The Aoudad (pronounced “AH-dad”) is native to North Africa and was introduced to Texas for hunting in the late 1950s. Some wildlife experts estimate there may be as many as 40,000 living in the state.

“There isn’t a lot of research on disease transmission between bighorn sheep and native species like bighorn sheep. This makes it difficult for wildlife experts to monitor diseases and maintain animal populations,” said Dr. Logan Thomas, assistant professor at Kansas State University and former postdoctoral researcher under Dr. Walter Cook, associate clinical professor in the Department of Veterinary Pathobiology at VMBS.

“If we can measure disease exposure in both species, we can begin to understand how they may influence each other,” he said. “By analyzing samples from both types of animals, we were ultimately able to determine that they too can carry and transmit the same respiratory diseases.”

It takes two

Bighorn sheep and mountain sheep are important animals for Texas wildlife conservation and the state’s economy. In West Texas, both animals are hunted as game, and some landowners derive a significant portion of their income from charging hunters a fee to hunt on their land.

“Aoudads, in particular, are very economically attractive for hunting,” Thomas said. “Because they are a non-native species, there is no season or bag limit, which is very attractive to hunters.”

Although bighorn sheep are also a favorite game animal for hunters, they require intensive management in Texas to maintain their population numbers at a sustainable level.

Respiratory diseases, including pneumonia, which both species can share, have already taken a toll on bighorn sheep populations, raising concerns among experts about the effects these diseases could have on bighorn sheep, in addition to making the situation worse for bighorn sheep.

“When we have outbreaks of these diseases in bighorn sheep, we typically see two waves of population decline,” Thomas said.

“We see a decline in all age groups at the beginning of the epidemic. Then, another wave comes after the lambs are born: many of them do not survive because they have not been exposed to the disease and therefore do not have an immune response like the older mouflons.”

The problem is further complicated by the fact that some adult bighorn sheep will carry the disease for several years after the initial outbreak, meaning the population may never have a chance to recover.

“We’ve known about this cycle in bighorn sheep for some time, but no one has studied whether the same thing could happen in bighorn sheep or whether the two species could transmit these pathogens back and forth,” he said. “We don’t think this is going to be a significant health issue for bighorn sheep, but we’re interested in learning more as we continue our research.”

Keep a close watch

Now that researchers have confirmed that bighorn sheep can carry the same respiratory pathogens as bighorn sheep, wildlife experts can begin monitoring disease transmission within and between these populations.

“Based on previous reports of this family of diseases, it’s also possible that they could spread to mule deer, which would complicate things even further,” Thomas said. “We’re very interested in studying this in the future, as well as how these diseases affect aoudad populations, because they haven’t received as much attention from researchers as native species.”

“Ultimately, we want all of these animal populations to thrive in a well-managed balance in Texas,” Thomas said. “Disease surveillance is one of the steps we can take to help make that happen.”