Mange Cases Increasing in Black Bears

Mange takes its toll on canines, but now it’s also showing up in bears. Researchers are studying what's going on with this disease in coyotes, bears and other wild animals.

Mange Cases Increasing in Black Bears

Research is ongoing in Pennsylvania to find out why mange, which typically affects canines most frequently, is now being found in black bears in the Keystone State. (Photo: Pennsylvania Game Commission)

It’s a rough world out there. For some animals, it seems to be getting rougher.

Wildlife diseases are on the rise and the impact of those diseases may be getting more severe. For predator hunters, the most visible is sarcoptic mange, caused by a mite that burrows under an animal’s skin to feed and lay its eggs. It is the same mite that causes scabies in humans. Infected animals can suffer severe hair loss and even death, often from exposure.

The mite itself isn’t necessarily deadly. Instead, animals carrying high numbers of the mites develop severe itching, which leads to excessive scratching, which can then lead to hair loss and infection. One Yellowstone National Park wolf pack, known as the Druid pack, was essentially killed off as a result of a mange outbreak, says US Geological Survey research scientist Dr. Peter Cross. 

“The wolves that were part of the original reintroduction in 1995 were clean," Cross said. "They were inspected and medicated to make sure they would have a higher chance of survival when they were released. However, sometime around 2002, it showed up in a few wolves outside the park and then found its way to wolves inside the park."

Although they don’t know for sure, scientists who study the park’s wolves think mange may be increasing in prevalence. They aren’t sure how it got inside the park either. 

“A wolf may have gotten into a fight with an infected coyote or it may have picked it up from a kill site and then spread it to other wolves through contact,” Cross said. “We will likely never know.” 

Mange Affecting Bears

Outbreaks are fairly common in members of the canid family, in part because they are social animals and often share dens. However, an increasing number of black bears in the eastern United States are falling victim to mange. Pennsylvania seems to be the epicenter of the recent outbreak, but mange-infected bears have been found in Virginia, West Virginia, Maryland and New York, among other states. 

Scientists don’t know how many bears have it, but they do know that the number of infected animals and the range of infected animals are increasing. Nor are they sure why mange seems to be increasing in black bears in recent years. It is most often spread through direct contact. Bears, however, are solitary and the mites typically don’t survive long periods without a host. 

“One theory is that they are picking up the mites from bait piles left out for deer. Many of the cases we’ve seen started around the face and head, so it could be that mites fall off an infected animal and then attach themselves to a new host when it puts its nose in the bait to eat,” says Penn State University PhD student Hannah Greenberg, who is leading a study on mange in Pennsylvania bears. 

Those mites need a host to reproduce, but Greenberg says they can survive for up to three weeks with the right conditions. They seem to favor high humidity. Bait piles left out during the summer may be an ideal home until a new host comes along. Deer can become infected with sarcoptic mange, but it is rare for reasons scientists don’t yet know. They can also get demodetic mange, which is caused by a different mite.  

At the moment, there is no widespread risk to bear populations. Pennsylvania’s bear population has risen from about 4,000 animals in the 1970s to nearly 20,000 now, according to the Pennsylvania Game Commission. With more bears roaming the forests of the eastern United States, though, it is likely the rate of infection will only increase. And there is little that can be done to slow the spread. 

Part of Greenberg’s research involves treating infected animals with Ivermectin, an anti-parasite drug given by injection. Normally, animals are given three doses, but Greenberg is giving infected bears a single dose before releasing them. The animals are fitted with GPS collars so she can recapture them and examine the impact of the treatment. It’s too early to say, but it may be working. 

“One bear we captured last year had severe mange. He stayed in one relatively small area for about two months after we treated him, but he then traveled about 100 miles in six weeks. He was killed by a hunter, but he had gained 100 pounds and had a full coat. He looked very healthy,” Greenberg said. “It certainly isn’t realistic to try to treat every infected bear, but if we can treat the ones that we can capture, then we might be able to slow it down.” 

But that may not matter. Other mange-infected bears that were part of the study but were not treated with Ivermectin have fully recovered.

Mange may be relatively new in eastern bears, but it is endemic to large parts of North America and has been part of the landscape for at least as long as European settlers have been on the continent. It is also found in Asia, Europe, Africa and Australia, where it has played a role in the decline of wombat populations. Cross adds that mange has also led to a decline in ibex in parts of Europe and alpacas in South America. 

“It can be a serious threat if a population is isolated or already low, but in most cases, it tends to run its course. Some animals may die from the symptoms. Some may recover and some aren’t infected,” she adds. 

Mange Is Cyclical

Greenberg says it tends to run in 30-year cycles, and can act as a natural population control. When fox or coyote populations spike, mange can spread through a region quickly and knock down their numbers. However, population density doesn’t always seem to play a role in the spread of the disease, says Penn State assistant professor of veterinary entomology Dr. Erika Machtinger.

“New Jersey doesn’t have the same issues with mange in their bear populations. Nor does the Poconos area of Pennsylvania, but their bear densities are as high or higher than what we see here in central Pennsylvania," she said. "It likely has more to do with bear interaction within a unit of space and this may be caused, for example, by land use changes for logging or development, or other reasons that fragment habitats."   

Whatever the reason, local or regional populations can decline after an outbreak. Parts of North Dakota experienced a significant decline in red foxes and coyotes in 1996. A biologist with the US Fish and Wildlife Service told the Chicago Tribune that he is seeing “…no animals in some very large areas. You don’t even see tracks in fresh snow. In other areas, there is a very reduced observation of animals.”

Another biologist predicted coyote populations were down by as much as 25 percent and fox numbers had fallen by 50 percent or even more as a result of that mange outbreak. Populations of both species recovered, although fox numbers remain low likely as a result of the rise in coyotes in some areas.

The disease was actually used as a weapon of sorts around the turn of the 20th century. That’s when the Montana state legislature approved a law that allowed the state veterinarian to capture wolves and coyotes, infect them with mange and then turn them loose. The idea was that infected animals would mingle with other animals and infect them, ultimately eradicating both predators. 

According to a report written by Morton Knowles, the state veterinarian at the time, the plan worked to some extent. 

“I am constantly receiving reports from all over the state of Montana of stockmen finding dead or badly diseased wolves and coyotes that are easily killed, many of them being destroyed by a blow from a club, being so poor as to be unable to get out of the way,” he wrote.

Ranchers in eastern Montana said 95 percent of the remaining wolves and coyotes were “affected with the disease” and that bounty hunters “have practically abandoned that territory,” he continued.

Didn't Bother Coyotes

It may have put a dent in the population of both species at the time, but it certainly hasn’t had any long-term impact on coyotes. Upwards of 100 different mammals get it worldwide, but Greenberg, who has also been studying the disease in coyotes and foxes, says gray foxes don’t seem to one of them. 

“Nobody seems to know why,” she adds. 

That’s part of her study, though. Greenberg wants to know if grays in Pennsylvania have in fact been exposed to mange but are somehow immune to the mites. She wants to examine the genetics of the mites themselves to see if there are different types that affect coyotes, bears and foxes. 

“I also want to see if there is some sort of different immune response to the mites. Researchers almost never find mites on infected coyotes. They may have some sort of immediate immune response that somehow helps them shed the mites, even though the symptoms remain,” she says. 

But Greenberg needs samples. That’s where you come into the equation. 

“I’m hoping hunters and trappers will contact me when they catch a fox or coyote with mange so I can pick it up and use it for my research. I can travel or they can bring it to me, whichever is more convenient,” she adds. 

Hannah Greenberg can be reached at (717) 226-7464 or hsg14@psu.edu.

As an Amazon Associate we earn from qualifying purchases.


Discussion

Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.