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"Balding" Bears: Mangy Mystery in Florida

Brian Handwerk
for National Geographic News
January 14, 2003
 
The appearance of hairless black bears has become common on the western
edge of Florida's Ocala National Forest—and the animals are not a
pretty sight.

"My heart goes out to these bears," local resident Guy Marwick said earlier this week. "It was 27 degrees [Fahrenheit (-2.7° Celsius)] here this morning. The females are trying to den up, and they are doing it in cold soil with no insulation."

Marwick's property borders the national forest, where he's been observing bears for over 30 years. He first began noticing balding bears in 1999. "I'm really concerned," he said. "Without the fur, the thickets and vines are really working on their skin. They are a bizarre and pitiful sight."



The dramatic hair loss is caused by mange, a condition spurred by an outbreak of mites. Researchers seek to learn the cause of the mite outbreak, which they say may be an indicator of some larger health problem affecting the bears. What that underlying problem may be, however, has proven to be frustratingly elusive to wildlife biologists.

Since their first sighting in 1990, hairless bears soon began appearing more and more frequently, always in the same general area of the Ocala National Forest.

"What we kept seeing was bears showing up as road kill on the western edge of the Ocala Forest," said Mark Cunningham, a veterinarian with the Florida Fish and Wildlife Conservation Commission who has been tracking the disease for years. "They were found in a relatively small area centered on the town of Lynne. Compared to the rest of the forest, it's a smaller, fragmented area with development interspersed with woods."

To date, the infection appears to be contained to an area on the western edge of the forest. "We don't really know if it's spreading, but it's certainly not going away." Cunningham said.

Cunningham cautioned that some recent media coverage has overstated the scope of the crisis. "Numbers-wise, the problem is not that large," Cunningham told National Geographic News.

However, the bears living in the affected area have been hit hard.

Roughly 50 percent of the area's bears have the disease, including over 80 percent of the adult females. Even the few females that don't currently exhibit the mange-like symptoms show signs of previous infection.

Threat to Bear Health Appears Minimal

The disease appears here to stay—at least for the near future. While male bears seem to gradually recover from the affliction, most females are stuck with it for life.

The high female infection rate also spells trouble for the next generation of bears since infected mothers transmit the mites to their offspring.

Wildlife experts say the affliction causes the bears discomfort but doesn't appear to jeopardize their survival.

"It doesn't really seem to cause them too many problems," Cunningham said. "We don't see secondary bacterial infections, for example, which is a primary problem with mange in dogs. They do get a lot of insect bites in the summer, which can create skin problems. And they are not nearly as well protected from brush and briars."

"They can look pretty rough," Cunningham said. "But they appear to be just as fat and healthy as normal bears elsewhere in the forest."

Disease May be an Indicator of Other Health Problems

Cunningham and other researchers seek to discover if the balding bears really are healthy—or if they have other troubles that may be at the root of the disease. Every species of mammal, including humans, commonly has mites specific to that species. These individual mite species do not usually impact the health of the host animal unless that animal has larger health problems.

"The mange could be an indicator of some underlying problem," Cunningham said.

With dogs, such mites proliferate and cause similar problems when there is a problem with the animal's immune system, and that could be the case with Ocala's bears as well.

But theories are currently more common than answers. Cunningham speculates the affected bears could suffer from some type of genetic defect or poisoning from an environmental toxin or that the mites themselves are becoming more aggressive. "It could be a number of things. We really haven't ironed out exactly what," Cunningham said.

Answers Sought in Forests, Laboratories

Cunningham and his team are monitoring the geographic spread of the disease, as well as the fortunes of individual, tagged bears by observation and the use of remote cameras.

The fight is also being pursued in the laboratory, where Disney's Animal Kingdom is pitching in to help assess the condition of the bears' immune systems. Leading the research effort at Disney is Scott Terrell, a veterinary pathologist who likens his job to "a Quincy for animals."

Under his microscope, Terrell examines skin samples for infection, mites, and associated diseases. "We want to see what's it doing to the hair and skin," Terrel said. "Another challenge is to figure out what kind of immune cells the body uses to react to these mites. Hopefully we can someday find out if these animals are immuno-suppressed."

Despite the hard work of reviewing hundreds of biopsies, solutions are elusive. "We still don't know why [the bears] are getting the disease," Terrell said. "We're very much in the investigation phase. We're not treating bears or anything. We're just trying to find out what's going on."
 

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