WASHINGTON — After spending its formative years in the Southwest Washington woods, elk hoof-rot is moving to the Puget Sound area.
Over the last couple of years, researchers have made strides in understanding the bacterial disease that has been killing elk since it appeared in and around Cowlitz County in the late 1990s. However, they haven’t been able to stop the rot from spreading.
While the “core area” for the disease is still Pacific, Cowlitz and Lewis counties, “We also have confirmed cases in the last couple of years in Mason, Thurston, Skagit, Whatcom and King counties,” Washington Department of Fish and Wildlife Hoof Disease Coordinator Kyle Garrison said last week. So far, these appear to be isolated cases, but they are concerning to hunters, conservationists and researchers.
Scientists now understand that treponeme bacteria, which cause “digital dermatitis” in domestic livestock, are also the major culprit in so-called hoof-rot. The condition causes elk hooves to become deformed and brittle. The affected hooves often fall off, causing sores on the animal’s foot and leg. Hobbled, the elk often die of infection or starvation.
However, “There’s still a lot unknown about how the disease is transmitted, and how environmental conditions play a role in transmission,” Garrison said. Scientists believe the disease is both “polymicrobial” — meaning that other bacteria, viruses or fungi could be interacting with treponema to cause the condition — and “polyfactorial” — meaning that nutrition, environmental conditions and other factors could be setting the stage for hoof-rot.
“We suspect the pathogen can persist in wet soil, and that it can spread to new areas on the hooves of the animals, Garrison said. That may explain why disease prevalence has remained more or less steady in rainy SW Washington, while spreading more gradually to areas with different climates.
Over the last couple of years, WDFW has worked with Colorado State University, Washington State University, “citizen scientists,” hunters and other groups to gather as much data as possible. Citizens use online reporting tools to help WDFW get a sense of where the disease is popping up. Hunters are now required to report any sightings of limping or dead elk in certain areas.
WDFW staff send samples to labs, where researchers work on identifying the culprits. Recently, WDFW used a helicopter to conduct an “aerial survey” of one major herd. WDFW researchers are also halfway through a four-year “survival study” of some collared elk.
Still, the disease is not well-understood, even in cows, sheep and other domestic livestock, where intervention is easier and research conditions can be controlled.
“Treatments exist in domestic situations for dairy that involve antibiotics, foot baths, hoof trimming, but those are entirely impractical for elk,” Garrison explained.
Conducting research on a wild population of migratory animals is far more difficult.
“True disease prevalence is so hard to measure in the wild,” Garrison said. “In wildlife, we can never do a true census of animals. We never get to count or look at all of the animals we’re interested in.” Another challenge is that infected elk don’t appear to be sick until the late stages of the disease, when they start limping.
“When you’re trying to count elk in a moving helicopter,” Garrison said, “it isn’t really amenable to getting an accurate count.”
Currently, the best method for slowing the spread of hoof-rot is a ban on transporting infected hooves. That ban was recently expanded, “based on some new confirmations of the disease in counties that hadn’t been active previously,” Garrison said. Scientists hope the ongoing four-year survival study of collared elk in the Mount St. Helens herd will help them better understand the disease, and how it affects individual animals, as well as the herd as a whole.
Researchers at Colorado State University and the U.S. Department of Agriculture are “trying to identify what other bacteria in addition treponemes factor into the disease,” Garrison said. Washington State University also continues to study treponeme disease in collaboration with WDFW.
In the meantime, WDFW staff are updating their web content about elk and hoof rot, and recently held a public meeting to discuss prevention and control measures. Staff are also investigating reports of the disease outside of the established area as they come in.
“We certainly take the disease very seriously, and respond as soon as we can,” Garrison said. “In terms of how concerning it is, there are still a lot of questions about how it impacts the population. We also don’t know how the disease may behave differently outside of SW Washington.”