Researchers find shared respiratory pathogens in aoudad, bighorn sheep

Photo: Jeffrey/Adobe Stock

Investigators at the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) in College Station have discovered that aoudad sheep can catch and spread many of the same respiratory pathogens that regularly impact desert bighorn sheep, which share their habitat.¹ These researchers found aoudad sheep to be competent hosts, capable of maintaining and intraspecifically transmitting, Mycoplasma ovipneumoniae and Pasteurellaceae.² The aoudad sheep shed the bacteria for 53 days following exposure.^1,2

“There isn’t much research about disease transmission between Texas aoudad and native species like bighorn sheep. This makes it difficult for wildlife experts to monitor diseases and preserve animal populations,” Logan Thomas, PhD, assistant professor at Kansas State University in Manhattan, Kansas, and a former postdoctoral researcher with the VMBS’ Department of Veterinary Pathobiology, said in a news release.¹ “If we can measure the disease exposure in both species, we can start to understand how they might affect each other. By analyzing samples from both kinds of animals, we were ultimately able to determine that they…can carry and transmit the same respiratory illnesses.”

In the study, the aoudad sheep developed limited clinical signs, while pathological findings ranged from mild chronic lymphohistiocytic bronchointerstitial pneumonia to severe and acute suppurative pneumonia. Similar findings were noted in bighorn sheep. The investigators also reported their findings that demonstrate how aoudad sheep could pose a significant threat for disease transmission to sympatric bighorn sheep populations. There may be evidence of interindividual susceptibility, pathogenicity, and/or transmissibility, suggested by individual aoudad that maintain varying severities of chronic infection. The investigators suggest that those aoudads may be carriers who are continuously shedding pathogens.²

The respiratory diseases that the species can share, like pneumonia, have already posed serious threats to bighorn sheep populations in past outbreaks.¹ Conservation experts are now concerned that aoudad populations will have to face those same threats.

“When there are outbreaks of these diseases in bighorn sheep, we usually see 2 waves of population decline,” Thomas said.¹ “There’s a decline in all age groups when the outbreak first happens. Then there’s another wave after the lambs are born–many of them don’t survive because they haven’t been exposed to the disease and therefore lack an immune response like the older bighorns have… We’ve known about this cycle in bighorn sheep for a while now, but no one had studied whether the same thing could happen in aoudad or if the 2 species could spread these pathogens back and forth. We don’t suspect that it’ will be a significant health problem for aoudad, but we aim to learn more as we continue our research.”

Aoudad, also known as the barbary sheep, belong to the Bovidae family.³ The species originated in North Africa before they were introduced to Texas in the late 1940s for hunting purposes.3 Wildlife experts now estimate there to be more than 25,000, and possibly as many as 40,000, currently living in the state.^1,2 Aoudad are still commonly hunted as game, as are bighorn sheep, and are considered some of the most economically significant game animals in the state.

“Aoudad, in particular, are economically valuable for hunting opportunities,” Thomas said.¹ “Since they’re a nonnative species, there are no season or bag limits, which [makes them] very attractive to hunters.”

Wildlife conservationists will use these new findings to better understand the relationship between the 2 species that share the Trans-Pecos region in Texas. With the knowledge that aoudad can carry the same respiratory pathogens as bighorn sheep, there will be a new emphasis placed on monitoring the disease transmission between the populations.

References

1. Texas A&M Researchers Find That Aoudad, Bighorn Sheep Share Respiratory Pathogens. News release. Texas A&M Veterinary Medicine and Biomedical Sciences News. August 22, 2024. Accessed August 29, 2024. https://vetmed.tamu.edu/news/press-releases/aoudad-respiratory-pathogens/
2. Thomas L., Clontz D., Nunez C., Dittmar R., Hernandez F., Rech R., Cook W. Evaluating the transmission dynamics and host competency of aoudad (Ammotragus lervia) experimentally infected with Mycoplasma ovipneumoniae and leukotoxigenic Pasteurellaceae. PLoS One. 2024;19(7):https://doi.org/10.1371/journal.pone.0294853
3. History of Aoudad Sheep in Texas. Outdoors International. Accessed August 30, 2024. https://outdoors-international.com/history-of-aoudad-in-texas/