A little heralded research letter was published in the Dec. 12, 2018 issue of the academic journal, Emerging Infections Diseases. In it was the potentially explosive information that Mycoplasma ovipneumoniae—the bacterium that causes pneumonia in domestic and bighorn sheep and often referred to as “movi”—is found in many different species, not just sheep.
“This bacterium was thought to be host-restricted to the subfamily Caprinae, but we describe its identification in healthy moose, caribou, and mule deer, and diseased mule and white-tailed deer, all species in the subfamily Capreolinae,” summarized the letter’s authors.
The primary author, Margaret Highland, is a USDA veterinary medical officer and frequent expert on the disease in bighorn sheep.
The Caprinae subfamily includes sheep (both wild and domestic), goats (both wild and domestic), and ibex. The Capreolinae subfamily refers to “new world deer” such as moose, elk, deer, and caribou.
In describing their research effort, which involved collecting nasal swabs from hundreds of animals (both captive and free-roaming) within the Capreolinae subfamily, the authors outlined that they had found myco present in slightly more than 2 percent of the samples. These myco-positive samples came from both healthy animals and those exhibiting signs of respiratory disease.
In describing a review of existing literature, the authors additionally note that the bacterium has been documented in antelope in Qatar and cattle in Colorado, neither being in either the Caprinae or Capreolinae subfamilies. Unfortunately, those reports did not include information on how the bacterium was identified. The letter repeatedly refers to movi as “fastidious,” contextually meaning that it is difficult to isolate and identify.
The letter explained that the findings are important “because current dogma regarding host specificity may dissuade laboratories” from looking for the difficult-to-isolate myco in other species.
Simply put, the letter describes a situation where, because movi is so often found in members of the Caprinae subfamily, the research world doesn’t look elsewhere for it. It is effectively a self-fulfilling prophecy.
Industry importance
Though not addressed in the letter, these findings could have valuable ramifications for the U.S. sheep industry.
It is popularly held that pneumonia-related death rates in wild bighorn sheep are due to movi infections. Domestic sheep grazed on ranges that overlap with bighorn territories are blamed for spreading movi to bighorns.
This has been the general argument behind numerous petitions and lawsuits launched by anti-grazing organizations against sheep grazing on public land. In some cases, such efforts have been successful in reducing or removing sheep from various allotments when it is possible they will come within 20 miles of bighorn territory.
There has been more scientific pushback against these arguments, however. Movi is not the only pathogen that causes deadly pneumonia in bighorns, and even before the findings outlined in the research letter, it was known to be endemic in bighorn territory.
Additionally, research conducted at Washington State University was unable to induce deadly pneumonia in bighorns solely by exposure to movi. It was only when movi infection was combined with another pneumonia-causing bacterium that fatal pneumonia was observed in some of the research animals.
Nonetheless, new lawsuits are regularly launched that assert the blame for bighorn pneumonia die-offs lies on the shoulders of domestic sheep.
On Jan. 30, for instance, the Western Watersheds Project and WildEarth Guardians filed a suit against the U.S. Forest Service, alleging that it knowingly risked populations of bighorn sheep in the Rio Grande National Forest when it allowed a new grazing allotment for domestic sheep near Creede, CO. — WLJ
