Environmental Almanac: Tularemia suspected in beaver deaths
EDITOR'S NOTE: Rob Kanter is away this week, but he sent this piece from Urbana resident John Palen, who taught for 26 years at Central Michigan University, where he was a professor and chairman of the journalism department. A reporter and editor at several daily newspapers in Missouri and Illinois, Palen was the editor of the Midland (Mich.) Daily News from 1975 to '83 and published an independent alternative local government newspaper in Midland from 1999 to 2010. He moved to Urbana in May 2011 and is an East Central Illinois Master Naturalist.
A beaver die-off at Urbana's Meadowbrook Park, thought to have been caused by tularemia, has emphasized the importance of keeping pets indoors or on a leash, for their own safety and that of wildlife.
It also has raised questions about the impact of drought, overpopulation and habitat destruction on wildlife. Officials say there are no reports of human illness.
What is known for sure is that seven of the beavers that thrived in and along McCullough Creek in the park died in the last year. The cause is less certain.
"There is no conclusive evidence," researcher Nohra Mateus-Pinilla said, "but it appears that the only thing that could have caused the die-off is an outbreak of tularemia."
She emphasized that tularemia bacteria are common.
"They are present in rabbits and squirrels," she said. "They are part of the natural ecosystem."
Mateus-Pinilla, a wildlife veterinary epidemiologist at the Illinois Natural History Survey, said it is possible that severe drought exacerbated the outbreak, with low water levels forcing beavers and other animals to live in closer quarters. Continuing destruction of wildlife habitat has a similar effect, she said.
Derek Liebert, project manager at the Urbana Park District, said a wildlife biologist suggested to him that if tularemia is in fact the cause, the die-off may be a corrective measure for a population that grew too large.
The Champaign-Urbana Public Health District issued an alert notifying residents of tularemia in the area. The alert cited a Meadowbrook beaver diagnosed with clinical symptoms of tularemia and an unrelated 2011 outbreak among five pet cats in Champaign, Urbana and Savoy.
Health district planning director Awais Vaid said people should not let their pets roam and should take them to a veterinarian if they exhibit symptoms such as loss of appetite or difficulty with movement. People who see sick animals in the wild or along trails should not approach them, Vaid said, not only because of the risk of tularemia but of rabies.
The park district warns Meadowbrook users to keep pets leashed and to stay on trails in the park. Mateus-Pinilla reinforced local government warnings about allowing domestic animals to roam or run unleashed.
"Then you are bringing them into your house, where there is direct contact. That is more serious," she said.
According to the National Institutes of Health, tularemia is common among wild rodents and can be transmitted to other animals and humans through direct contact and by ticks, biting flies and other insects. In humans, tularemia bacteria can cause illness ranging from asymptomatic to life-threatening.
Liebert said the first dead beaver was found in January 2012. It was taken to the University of Illinois veterinary diagnostic laboratory, where tests were conducted, with inconclusive results. Then in June and September, two adult beavers were found dead but were too decomposed to be necropsied, he said.
The biggest spate of deaths occurred in October, when three beavers were found, two of which were necropsied. In November, a seventh beaver was found. Liebert said the most recent sighting of a live beaver, a single individual, occurred Dec. 19.
The effort to isolate the cause of the deaths was hampered by several circumstances, Mateus-Pinilla said. One is that decomposition sets in rapidly, and sometimes there is not much a pathologist can do because of the condition of the body. The "gold standard" for a confirmed diagnosis, Mateus-Pinilla said, is the ability to grow a culture of the suspect bacteria. The Meadowbrook beavers were tested for several pathogens, including tularemia, salmonella, leptospira and canine distemper. No cultures resulted.
However, investigators were able to rule out toxins, such as from run-off, and also found evidence pointing to tularemia, even if it did not amount to a confirmed diagnosis.
Mateus-Pinilla said salmonella and leptospira were eliminated, for example, because salmonella would not have caused a die-off, and leptospira is associated with lesions not found in the necropsies. But investigators did find certain changes in the lungs typical of tularemia. In the end, Mateus-Pinilla said, what signs there were pointed to tularemia.
Mateus-Pinilla said it is unlikely that the habitat provided by the park itself was to blame. Indeed, she said, the fact that beavers were thriving there "tells us it was a suitable habitat." Unfortunately, she said, the die-off "also tells us that natural habitats are more and more disturbed, forcing the beavers to be in a more dense population."
Human attraction to nature puts people in closer contact with wildlife diseases, she added. "We want to put our house in the woods," and as a result "we are getting closer to diseases that we wouldn't find in the middle of New York City."
Mateus-Pinilla sees an opportunity for independent research through close monitoring of future colonies at Meadowbrook.
"I would love to see it happening," she said. The Meadowbrook beavers are "close to one of the biggest wildlife research institutions in the United States. We have the resources, and we have the students."
More information about tularemia is available at http://www.cdc.gov/tularemia/.