Discovering the ‘how’ in elk hoof disease

Dr. Margaret Wild, the Washington State University College of Veterinary Medicine scientist heading up the effort to study hoof disease in elk, will soon be retiring.

She recently summed up what that effort has accomplished, as well as the next steps she sees as necessary to move forward the management of the disease.

The university has already started a search for Dr. Wild’s replacement.

Dr. Wild has spent much of her career researching Chronic Wasting Disease in deer. She carries a doctorate in zoology, a bachelor’s in wildlife biology, and a doctor of veterinary medicine from Colorado State University.

Treponema Associated Hoof Disease (TAHD) is a bacterial disease that has severely impacted the elk herds in Southwest Washington, and has spread to other parts of the state, as well as other states across the west. The disease attacks the hooves of the elk, causing lesions and deformities, eventually crippling them.

It was first detected in the Mt. St. Helens herd in 2008, and has cut that herd’s population in half over the last 17 years. As the disease spread, it also spread alarm, and eventually the WDFW and WSU teamed up to see what could be learned about TAHD, and what might be done to mitigate its effects.

The research has been conducted at many levels, including data collection and analysis, laboratory research to identify bacteria involved, field work to study the environment where the disease prospers, as well as studies involving captive elk.

Research quickly identified the main bacteria that was fueling the disease, treponema, but recent research has shown it actually works in concert with other bacteria. Treponema does not cause the symptoms by itself.

“There are a couple other bacteria that are also important,” Wild said. “They probably work together and are what causes the legions. They attack those cells that are at the beginning of where the hoof grows.”

“In the sole of the foot we see a lot of ulcerations and dead tissue,” she continued. “The bacteria are affecting the bottom of the foot and also the soles along where the hoof starts growing.”

The wet conditions of Western Washington have always been thought to be contributing to the rise and spread of the disease. Much of the research bears that out.

Kyle Garrison, the WDFW ungulate section manager, has been closely following the work, and he pointed out that TAHD is very similar to digital dermatitis in domestic dairy cattle, which also live in a wet environment.

“Dairies are often wet and you have this slurry the cattle are standing in all day,” he said. “The hypothesis is, you are standing around in wet conditions, and it weakens your skin. You are now more prone to abrasions where bacteria can get in.”

Soil composition apparently plays a part, too. Wild reported the research showed a clear correlation between clay in the soils and the disease.

“With each percent increase in soil clay there is an associated increase in the odds of TAHD,” she said.

When precipitation was considered, the data was incomplete.

“We could not tease out precipitation,” she said. “We need data from the drier areas to compare. If we could collect harvest locations than we would have the data we need to make that comparison.”

The prevalence of the disease within the herds in drier climates does appear to be lower than in the wetter areas. For instance, the disease is present in Eastern Washington, but so far has not become as common within the herds as in the western part of the state. In Western Oregon and Northern California, it also seems more prevalent than in drier zones.

The research has also looked at habitat, as well as the habits of the elk herds, and what effect that may have on the disease. In addition to clay soils, agricultural practices apparently play a part, as does elk behavior.

“As the proportion of time spent on agricultural land, which can be either pasture and hay or crops, increases there is also an increase in the odds of elk harvested in those areas of having TAHD,” said Wild, “so agricultural and clay soils are contributing to transmission.”

“That is happening in a couple ways. Elk are congregating in those areas, and where elk congregate there is an increase in the transmission. They like to find places like pastures that are easy to live in. They have good high-quality forage, and some time they will become more sedentary.”

So, instead of moving over large areas they can become pretty stationary and hang out in the lower valleys.

The captive elk research has also born fruit. Being able to control the conditions for captive animals can be insightful. However, the treponema bacteria have proven hard to replicate.

“Treponemas are hard to grow in the laboratory,” Wild said. “There are some things we can’t do because they are really hard to grow. What we were able to do was enrich the treponema. It’s not a pure culture; it’s a mixture of bacteria working together.”

In order to test the transmission of the disease, the scientists used material from animals infected with treponema. The pathogen proved to be easily transmissible, and the inoculated elk had lesions in only two weeks, and in four weeks the animals were successfully infected with treponema. This means the disease is easily transmittable.

The research will continue, but Wild pointed out how hard it can be to treat a disease among animals in the wild. There has been some push toward possibly aiding the elk by placing nutrient blocks out for the them. However, that may actually increase the spread of the disease by congregating the elk, which aids in the transmission.

She also referenced the fact that scientists have been unable to control digital dermatitis in dairy cattle. Wild’s point was that if this has not been possible, even though the animals are contained in a domestic setting, imagine how difficult it would be to do so with animals in wild environs.

“If you can’t even cure a disease when you have your hands on the animals everyday it’s a big ask to try to cure it in the wild,” she said.

While it may never be possible to eradicate TAHD entirely, certainly there may be ways to mitigate its prevalence.

As Dr. Wild prepares to pass on the torch, she spoke to what she has accomplished.

“What I am most proud of is I think we’ve uncovered some really good foundational information,” she said, “and that next person can come in and build off of that. We know we have an infectious, transmissible disease now, and we can reliably reproduce it in the captive animals. We know where to take the next steps looking at risks that the individual animals have. We have also really improved diagnostic detections for the pathogens.

“I am proud of all the foundational knowledge that we have created that is going to help the next person do more exciting research.”

Wildlife lovers, hunters and others are hoping those next steps will lead to healthier elk herds in the future.