A disease that has mangled the hooves of elk in Western Washington and other parts of the country is affecting more than just the animals' feet, according to a new study from Washington State University.
The study, published last month in the journal Scientific Reports, suggests that treponeme-associated hoof disease, or TAHD, is causing systemic molecular changes throughout the animal.
Scientists at the university examined knee tendons from elk to look for changes in its epigenetics — molecular factors that regulate gene activity. The analysis found significant epigenetic changes in samples from animals that had TAHD.
Michael Skinner, a molecular biologist at Washington State University and one of the authors of the study, said because the tendon isn't in the part of the animal impacted by the disease, that likely means the disease is altering cells throughout the body.
"It's a much more broad effect on the elk than just its hoof," Skinner said.
The study was the first of its kind for the disease, which only affects elk. It also notes that it's possible the alterations are passed down through generations, and that it could mean mutations that make an animal more or less likely to catch TAHD are being passed to newborn elk.
TAHD is a bacterial infection that causes lesions and deformities in an elk's hooves. It can cause one part of the hoof to grow longer than the other, create painful lesions and lead to the hoof falling off completely. Elk that become infected often are seen limping, and deformed hooves can make it harder for them to get food or run away from predators.
The Washington Department of Fish and Wildlife first encountered the disease in 2008 in southwestern Washington. It has since been reported in 17 counties, most of them west of the Cascades.
"It's all throughout Western Washington," said Brendan Oates, an ungulate specialist for WDFW.
Other detections have been confirmed in Idaho, Oregon and California.
Wildlife officials and researchers track the disease through reports from hunters and abnormal-looking hooves that hunters submit for testing.
Oates said he doesn't have hard numbers for prevalence, but said that between 10% and 15% of hunters in Western Washington who report information about their elk are seeing abnormal hooves. The disease is particularly common in the elk herd near Mount St. Helens — roughly 25% of hunters who submit reports on elk killed there report hoof abnormalities.
Margaret Wild, a biologist at WSU and one of the other authors of the study, is leading a team of researchers looking at the disease. They have spent the past several years building out their baseline knowledge, from how it infects elk to how it spreads to what it does to the animals.
"Right now, we just have all these pieces of a puzzle and we're trying to put them together," Wild said. "The more pieces of the puzzle come in, the more clear a picture we'll have."
Some of her work involves captive elk at the university, but much of it relies on samples submitted by hunters, which usually include the hoof and a few inches of the leg. Researchers try to use the sample in as many ways as possible. They can inspect the hoof itself, and then they can use other parts of the sample for other studies.
That's how the epigenetic study was done. They used tendons from a mixture of Rocky Mountain elk and Roosevelt elk samples from five states, some infected with TAHD and some not.
Skinner, the other WSU researcher, did the analysis of the epigenetics in specific cells within the tendon. In doing so, he can see whether certain genes were turned on or off — an epigenetic mark.
Environmental factors can cause those marks in an animal, but in the case of this study, he found that the marks only in the diseased animals. Those marks can be passed down to offspring.
More research would be needed to confirm that is what's happening in this case. Some other basic questions are still unanswered — like why the disease is creating epigenetic alterations, and how those changes impact an individual elk.
But confirming that it is causing a change is the first step, and it sets the stage for more studies in the future.
"Now we know a change has occurred," Wild said. "We don't know why or what the impact is, but over time we can use that as foundational information to continue to learn more."
