Sunday, February 5th, 2023
Sunday, February 5th, 2023

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Pennsylvania Game Commission stops use of ivermectin to treat bears

Harrisburg —A Penn State study has changed the approach taken by the Pennsylvania Game Commission when it comes to treating bears with mange.

When encountering a bear with mange during nuisance or research trapping, the Game Commission would treat the animal with a dose of ivermectin if the case wasn’t severe.

According to Emily Carrollo, the agency’s black bear biologist, the Penn State study documented that about 80% of bears with mild or moderate cases of mange recovered within one year, regardless if they were treated or not.

As a result, she said, the Game Commission no longer treats bears with mange.

“While this is the first time we looked at documenting recovery from mange
infections in Pennsylvania bears, we have known for a while that mange
has not had any population effects despite being found in the population
since the early 1990s,” Carrollo said.

“For the last 30 years, the bear population has continued to grow even while
mange spread to different parts of the landscape in the bear
population, so we knew there had to be some level of bears that
recovered from mange, and this study helped us identify that number.”

Carrollo did point out that bears with severe cases of mange did have slightly
higher recovery rates if they were treated with ivermectin. However,
recovery rates for severely infected bears were low overall for both
treated and untreated individuals.

One factor limiting the effectiveness of ivermectin with bears was the
ability to only give an animal one dose. The proper way to administer
ivermectin is through multiple doses to completely eliminate the
infection, Carrollo said, and this wasn’t possible to do with a wild
animal.

“We weren’t sure if this kind of application of ivermectin was really making a difference. This study showed it didn’t, and thus we decided to stop treating bears with mange infections,” she said.

The use of ivermectin on wild animals with mange, such as bears, also comes with
many downsides, according to Andrew Di Salvo, Game Commission wildlife
veterinarian.

The risks include promotion of drug resistance, interference of genetic selection amongst
wildlife for genotypes that may be naturally resistant to infestation,
and potential perpetuation of a more intense hypersensitivity reaction
should treated wildlife be re-infested with mange, he explained.


“If the bear’s body condition is determined slightly below average or normal, regardless of skin condition, no medication is administered and the bear is released.”

— Di Salvo


“Ivermectin only kills adult mites, so remaining eggs, larvae, and nymphs often result in re-infestation,” Di Salvo said.

“In captivity, successful mange resolution requires repeated ivermectin
administrations over multiple weeks. This treatment protocol is
generally not possible to duplicate in free-ranging wildlife.”

While ivermectin is no longer an option for treatment of bears with mange, Di
Salvo said the emphasis is now on evaluating the body condition of
captured bears. The Penn State research found that body condition was
the best predictor of both mange severity and survival.

“If the bear’s body condition is determined slightly below average or
normal, regardless of skin condition, no medication is administered and
the bear is released,” Di Salvo said, adding that bears are always
released as close as possible to the capture location.

And those with suspected mange are never released to areas where mange has
not been documented. “If the bear’s body condition is poor or severe,
regardless of skin condition, it is euthanized.”

Mange is a highly-contagious skin disease caused by a mite, and historically
it’s been a sporadic problem with black bears, according to the Game
Commission.

In the early 1990s it began to be observed more frequently in bears, expanding
throughout much of the state. More than 50 bears are euthanized annually
by the commission due to severe mange infections.

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