From the road, Hannah Greenberg could see that the black bear’s face had gone completely bald. Hair hung off the rest of its frame in long strands, more like dreadlocks than a coat of fur.
When Greenberg, a graduate student in veterinary entomology, approached the animal with members of the Pennsylvania Game Commission as part of a new study, it stumbled and fell, unable to run as a bear normally would, she said. After the bear was tranquilized, the team weighed it and found it was just 45 pounds, less than half what they expected for an animal its age. “It pretty much had no muscle mass,” she said.
But the most shocking thing was the way the black bear smelled.
“It was just bad,” said Greenberg, who studies at Pennsylvania State University. “Kind of bitter, and a little bit like death.”
The cause of the black bear’s woes: Sarcoptic mange.
Black bears suffering from mange, a skin disease more typically associated with dogs, have become an increasingly common sight across Pennsylvania’s woods since the 1990s. But now, officials say, the Keystone State seems to be the epicenter of an outbreak that scientists don’t fully understand. With cases popping up in neighboring states such as New York, West Virginia, Maryland and Virginia, black-bear mange is becoming a mid-Atlantic regional issue, said Mark Ternent, a wildlife biologist and the Pennsylvania Game Commission’s black-bear expert.
“Every week we get sightings reported of a bear on a trail cam where someone’s asking us, ‘What’s wrong with this bear?’ ” Ternent said.
Mange is caused by the microscopic mite Sarcoptes scabiei, a parasite that afflicts more than 200 species, including humans. The mites burrow into an animal’s skin, where they dig tunnels and slurp naturally occurring liquids. Normally, this doesn’t cause much more than some itching or irritation, but in extreme cases an infestation can lead to extensive hair loss and an immune response so strong it can kill the host animal.
“It’s a spiraling decline,” Ternent said. “Nutrition goes down, the bear spends a lot of time scratching, and it might not be foraging or hibernating as efficiently as a healthy bear. As their health declines, their immune system is affected and the mites become more prevalent.”
That smell Greenberg mentioned? It was probably caused by a secondary infection on the bear’s skin, probably yeast. Some bears can recover, Ternent said. But in others, all of these maladies eventually build to the point that a bear can die of starvation or a related complication.
Although mange is hardly an emerging disease, it is relatively new to black bears. Historically, mange in bears was relatively rare, with cases being documented by scientists only occasionally. That is probably because mites can’t survive long away from their host, which means they are usually spread by contact. This works well for the mites that reside on social animals such as coyotes. But bears are mostly solitary when not breeding or raising cubs, Ternent said.
These days, the Pennsylvania Game Commission estimates that about 50 mange-infected bears die each year — killed by the disease or after being trapped and euthanized by state officials who deem the animals’ condition untreatable. That’s a relative drop in the bucket of Pennsylvania’s population of about 20,000 black bears — a record number for the state — but “it is something that’s got our attention,” Ternent said.
The growing bear population makes it difficult for wildlife managers to know whether mange is on the rise or whether cases are increasing along with bear numbers, Ternent said. One thing is clear: With more trail cams and smartphone cameras in the woods, sightings are on the rise.
Rather than wait to see what happens, a team of scientists has set out to study the scourge in real time. This year, Ternent and a team of collaborators trapped and fitted 36 bears with Global Positioning System collars — 12 that were perfectly healthy, 12 with mange and 12 others with mange that the scientists dosed with an injectable anti-parasite drug called ivermectin.
The drug works well in dogs, but it’s most effective in two doses — one to kill established mites and a follow-up to nix any hatched eggs. Scientists try not to re-trap bears, because it stresses them and might habituate them to human contact. So the study will determine whether one dose of ivermectin can help bears kick infestations.
“The collars will probably remain on for about five years,” said Erika Machtinger, a veterinary entomologist at Penn State and the study’s lead researcher. “We’ll have a pretty good long-term analysis of the bears that are currently infected, so we can see if they become reinfected, or what happens during hibernation, or how it might affect [fertility] levels or offspring. Hopefully we’ll be able to have a much better understanding of what’s going on.”
The answer might be that mites’ genes are mutating, creating a new variety that specializes in bears. Or it could be that climate change is altering the microhabitats that mites target on bears, making it easier for the parasite to survive, Machtinger said. Or maybe some shift in the mites’ microbiomes — the bacteria and fungi they rely upon to survive — has allowed the critters to better feast on black bears.
It is probably a combination of factors, she said. But the team has projects designed to follow every lead, including an examination of how many ticks the bears carry, to see whether there’s a correlation between one parasite and another. Bears harbor “lots and lots and lots of ticks,” Machtinger said — so many that when the researchers count ticks on bears they’ve trapped, they limit the search to three minutes. The results are recorded in hundreds.
As part of its efforts, the game commission is asking residents to report any bears they see with hair loss to their closest regional office. They’re also suggesting that people secure their trash cans and reconsider leaving food out for wildlife.
“Say you have a feeder out for deer because you like to see deer, and bears are coming in,” Ternent said. “If just one of those bears is infected with mange, well, then you run the risk of infecting all the other bears.”
“Any time that there’s animal-to-animal contact or a place where an infected animal has been, it’s probably a risk factor,” he added.
While seeing a bear stricken with mange is a harrowing experience, Greenberg, who is a student in Machtinger’s lab, said it gave her a sense of purpose.
“They’re such hardy creatures, and to see it looking like that, it just really pulls at your heartstrings,” she said. “But that’s why we’re trying to solve this.”
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