Study: Multiple bacteria involved in elk hoof disease

There’s more than one bacterial culprit for a disease that’s been eating away at elk hooves in the Pacific Northwest.

A new study from Washington State University found that at least two separate bacteria are behind treponeme-associated hoof disease, or TAHD.

Researchers already knew about the bacteria responsible for the “T” in the disease’s acronym – treoponema spirochete bacteria. This study, which was published in the journal Applied and Environmental Microbiology, confirmed that bacteria’s role and identifed mycoplasma as another bacteria associated with the lesions caused by the disease.

The paper also found that both bacteria were present in hooves sampled from across the study area.

Liz Goldsmith, the lead author of the study, said that shows the disease looks similar across the northwest, regardless of the level of prevalence in a given herd. The same bacteria are rotting hooves in both central Idaho, where the disease is still considered sporadic, and in places where it’s become endemic, like southwestern Washington.

“Showing that strong geographic consistency is important for thinking about management of the disease,” Goldsmith said.

Margaret Wild, the veterinarian who leads WSU’s hoof disease work, said geographic consistency helps researchers rule out at least one possible reason why the disease’s prevalence varies so much from one region to the other.

“The difference in prevalence between these areas is probably not because of the bacteria that are present,” Wild said. “It could be something in the environment or it could be something in the elk.”

It’s the latest study to come out of the lab at WSU dedicated to studying TAHD, a condition that causes lesions and deformities on elk hooves and can lead to the hoof falling off completely. Infected elk are often seen limping.

The Washington Department of Fish and Wildlife first confirmed the disease in 2008 and it has since spread throughout the western part of the state. An online map also shows that elk in Walla Walla County have tested positive for the disease.

Idaho detected its first case of the disease in 2019. Cases have also been found in Oregon, California.

Since its discovery, researchers have been trying to learn all they can to understand how the disease works. The lab at WSU, led by veterinarian Margaret Wild, has spent years filling out the baseline knowledge of the disease with study after study.

Another recent study looked at how soil composition might affect TAHD risk. It found that TAHD cases were higher in areas with clay soil and agricultural land.

Goldsmith’s paper analyzed lesions from 129 hoof samples from free ranging elk across the West. The samples came from elk in areas where the disease is endemic, like western Washington and northern California, and where it still occurs sporadically, like central and northern Idaho and eastern Oregon and Washington.

State and federal wildlife officials gathered the samples between 2018 and 2021 and submitted them to the Washington Animal Disease Diagnostic Lab in Pullman.

In the lab, they tested the hooves for the disease and looked at the bacteria present.

Mycoplasma bacteria were found exclusively in TAHD-positive lesions, according to the study, and they were strongly correlated with the treponema bacteria. That suggests that the disease is “polybacterial,” rather than being caused by one type of bacteria.

Goldsmith said knowing that multiple bacteria are involved is important.

“That really changes how we might think about diagnosis or further investigation of the disease in the future,” she said.