Scientists researching the cause of elk hoof disease in Southwest Washington have more questions than answers about the condition that causes the animals to limp in pain.
After a seven-hour meeting in Vancouver this week, members of the Washington Department of Fish and Wildlife’s hoof rot technical advisory committee came up with three statements they could agree on about their knowledge of hoof rot — and more areas that warrant continued research.
Topics that need more research include:
o Whether hoof disease is being maintained in elk populations.
o How elk movement and habitat use relates to hoof disease.
o Whether elk can develop immunity to hoof disease.
o What effects hoof rot has on elk survival and reproduction.
o How the disease progresses over time in individuals and herds.
o How it’s transmitted.
o Whether it’s present in fecal and soil samples.
Reports of lame elk or elk with overgrown or missing hooves in the Cowlitz River basin began in the mid-1990s and have spread throughout Southwest Washington.
WDFW’s expert group, which in includes veterinarians and PhDs, have met several times as the agency works to identify the cause of the disease. Researchers have sent tissue samples from diseased elk to five diagnostic laboratories as far away as England.
Topics that need more research include:
o Whether hoof disease is being maintained in elk populations.
o How elk movement and habitat use relates to hoof disease.
o Whether elk can develop immunity to hoof disease.
o What effects hoof rot has on elk survival and reproduction.
o How the disease progresses over time in individuals and herds.
o How it's transmitted.
o Whether it's present in fecal and soil samples.
At meetings and in publications, WDFW has indicated that researchers believe the disease is caused by the treponeme bacteria, which has been linked to hoof disease in cows and sheep in many parts of the world.
The researchers who convened this week were cautious in assigning blame to treponema, however, agreeing that hoof rot “most resembles and shares many features with treponeme-associated CODD,” which is short for contagious ovine digital dermatitis, a condition in sheep.
Another area of agreement is that “available evidence is most consistent with an infectious bacterial disease,” not mineral deficiencies or exposure to herbicides that some people have suggested.
The scientists also agreed that environmental factors, including wet conditions, are likely important in the spread of the disease. Biologists have said they don’t expect it to spread to drier climes east of the mountains but wouldn’t be surprised if it spread to western Oregon.
Jennifer Wilson Welder, a research microbiologist for the U.S. Department of Agriculture’s National Animal Disease Center in Iowa, said hoof rot can be transmitted between sheep and cows, but it’s unknown if it can move from domesticated animals to wild ones. Elk hoof rot was first spotted in the Boistfort Valley in Lewis County, which has some farms.
Welder said cows with hoof problems can be treated with foot baths several times a week but there’s no vaccine to prevent it. “I can’t imagine what you guys are going to come up with when you’re looking at a wild population,” she said. “There still a lot of questions and we don’t have answers.”
The researchers heard a presentation from Boone Mora, a retired public health researcher who lives in Skamokawa. He thinks hoof disease is caused by leptospirosis, a disease that can be transmitted from animals to humans.
Mora said leptospirosis is the world’s most common disease that can be transmitted between animals and humans. However, it’s difficult to diagnose, he said, and it’s common for epidemics to go undiagnosed.
“It fits the problem better than anything else and it warrants thorough investigation,” Mora said. Group members didn’t respond to his suggestion.
The group also heard a presentation about herbicides by Anne Fairbrother, a veterinarian and principal scientist with the Exponent research company in Seattle.
Herbicides have “no known mode of action in mammals,” Fairbrother said. They’re “practically nontoxic to mammals according to most of the studies that have been done. We haven’t had any observations of direct effect that we’ve been aware of on wildlife and most of these herbicides have been around for several decades.”
The group briefly discussed how effective culling of herds would be to prevent the spread of hoof rot.
Kristin Mansfield, a WDFW vet, said that shooting all the limping elk would theoretically select for the animals genetically resistant to the condition.
For a video of elk with hoof disease in the Winston game unit
https://www.youtube.com/watch?v=ibXoI9JM23I
