Growth of black bear mange proves a continuing mystery
Black bear populations are growing all across the Northeast, from Pennsylvania to New York to Maryland to New Jersey.
So, too, is mange.
The question is why.
There's no doubt as to what mange is. It is, according to the Cornell University Wildlife Health Lab, "a skin disease that affects mammals caused by microscopic mites that burrow into skin."
There's no confusion over the particular variety of mite that's causing so much problems for bears either. In black bears, the university says, sarcoptic mange is usually the issue.
And finally, there's no ambiguity in regards to what mange in bears looks like. It always exhibits certain symptoms: hair thinning, hair loss, thickening and wrinkling of the skin, scabs and foul-smelling crusts. Bears afflicted sometimes die.
The befuddlement is why mange is, suddenly, so common among black bears.
It's not like it was unheard of before. Historically, mange would periodically show up on the landscape, but just here or there, said Justin Brown, wildlife veterinarian with the Pennsylvania Game Commission. It affected individual animals.
But the disease never became so widespread as to be noticeable beyond that.
"Unfortunately, the situation's a little bit different in Pennsylvania," Brown said.
That's not to say mange is "raging" across Pennsylvania, he said. But it is becoming more common.
It was isolated to the west-central region of the state in the late 1980s and early 1990s. Since, he said, it spread across most of the state's bear range.
It still comes and goes, he said. But cases of it, and the impact, are greater.
Mange will show up in an area and impact a lot of bears for two to three years, then die down or go away, only to spring up somewhere else.
"Hot spots come and go," Brown said.
It's not just that the disease is becoming more common because bears themselves are more common either, he said. There's something else going on, he noted.
The commission examines every bear it can. It handles road-killed animals, those taken by hunters, those caught in order to be collared and those euthanized when mange becomes debilitating.
"In all of those different measures, we're seeing increases," Brown said.
The why of that is a mystery, however.
The commission — together with its counterparts in New York and elsewhere — is learning some things.
One is that the mites that cause mange can't survive certain conditions.
A graduate student at the University of Georgia examined mites, specifically to see how they respond to temperature. They found that at spring-like temperatures, mites live one to four days. At summer temperatures, they can survive six to 12.
When temperatures drop below freezing, though, mites go dormant.
"That is important," Brown said. "We're not dealing with an environmental reservoir. So it's not like chronic wasting disease, where if a mangy bear comes into a yard or into an area those mites are going to be there forever."
That has implications, Brown noted.
For a long while, scientists thought bears needed to pass mites from one to another via direct contact, Brown said.
And that certainly can happen, he added.
But the Georgia research shows one bear can deposit mites into an environment – say around a bird feeder that attracts multiple hungry animals – that infect a second animal, long after the first has gone.
"What this tells us is, if you've got a mangy bear coming to a feeder or coming to a garbage can, whatever comes to that garbage can or feeder over the next seven to 10 days, depending on the temperature, could potentially be exposed to these mites," Brown said.
Indeed, according to Cornell, such "contaminated environments" can take all forms, including burrows, nests and the like.
So it's easier for bears to transmit mange to one another than was perhaps previously thought.
But does the growth in bear numbers — which puts more bears in contact with one another, or in the same areas as one another — alone account for increases in mange?
That's harder to say, Brown noted.
But some new research may offer clues.
The commission launched a new study this summer. Using an antibody test, it is collecting blood samples from bears still alive — with mange and without — to determine if those animals ever had mites previously.
"It will sort of give us an idea of, what is the prevalence of manage in different parts of the state. That will be a measure we can follow over time to say, is it getting worse, is it cycling through parts of an endemic area," Brown said.
Bears with mild cases of mange — after receiving treatment — get radio collars. The commission, together with researchers from Penn State University, are monitoring their behavior, movement and survival.
"Hopefully, that will give us a lot of better information on the impact of mange on individual animals, as well as our treatment efficiency," Brown said.