CORVALLIS, Ore. - An invasive sub-genus of lice that originated in Africa or Asia is likely to blame for "hair loss syndrome" in blacktail deer - and can cause the same condition in mule deer, according to researchers at Oregon State University.
In controlled tests at the E.E. Wilson Wildlife Area north of Corvallis, healthy mule deer that were put in a pen with blacktail deer infested with the lice, Damalinia (subgenus Cervicola), immediately attracted the parasites and soon began exhibiting hair loss symptoms.
"The lice were on them in no time, and the mule deer began scratching and rubbing very quickly," said Bruce Coblentz, a professor of fisheries and wildlife at OSU who worked with master's student Jason Robison on the study. "And it increased steadily."
Funding for the study was provided by the Oregon Department of Fish and Wildlife, the Oregon Hunter's Association, the Blacktail Deer Foundation and the Oregon Wildlife Heritage Foundation.
Hair loss syndrome is a debilitating condition that causes blacktail deer to constantly chew at their fur. They often become emaciated and many die, particularly during cold winters or in areas where food supplies may lack sufficient nutrition.
Coblentz said Damalinia (subgenus Cervicola) is a member of a family of chewing lice that originated in the Africa or Asia and is found on deer and antelope there. Because little is known about this sub-genus, it is difficult to determine how it came here.
"We don't know what its normal host animal is, though we can assume it's some kind of Old World (Africa or Asia) deer," Coblentz said. "It may have gotten here through imported exotic game species, the legal or illegal transportation of exotic game, or even from zoos. It's a pointed reminder of the unknown consequences of introducing non-native species."
Hair loss syndrome was first diagnosed in blacktail deer near Puget Sound in the mid-1990s. Since then, the syndrome has spread among blacktail deer populations with unconfirmed reports from northern California to southern British Columbia - on the west side of mountain ranges.
Thus far, the condition hasn't spread to mule deer populations east of the mountains, Coblentz said. But the OSU research shows that mule deer can be host animals - if the conditions are right.
"Our study focused on the deer themselves," Coblentz said, "but it is clear that we need to know more about the lice. We found ourselves looking at them more closely and finding some puzzling results that we can't explain."
Robison and Coblentz monitored deer at their research site for more than a year and found that lice numbers were low or non-existent in warm weather, and skyrocketed as the weather got colder. In May and June, almost all adult lice had disappeared, but huge numbers of nymphs - or offspring - stayed with host animals. But by August, they were gone, too. "The deer were essentially clean," Coblentz said.
Yet as the weather cooled, the lice reappeared. And so did the deer's symptoms.
"The literature says that lice cannot survive for more than 24 hours away from a host animal," Coblentz said. "We took some off of the deer and they survived for seven days. We even exposed them to near-freezing temperatures and, after warming, they came roaring back. So there may be some kind of egg/larval stage, or the lice may use an alternative host that not only keeps them alive, but may contribute to how the syndrome spreads. We just don't know."
When hair loss syndrome was first diagnosed a few years ago, almost all of the affected blacktail deer were found at elevations lower than 1,000 feet. Coblentz said that conceivably could relate to where the lice may spend time away from the host animals, though he points out that the "elevation cap seems to get a little higher each year."
"So far, the syndrome hasn't hit mule deer on the east side of the Cascades," Coblentz said, "But whether it's because of elevation, cold or pure dumb luck, we don't know."
None of the animals in the OSU test died from symptoms relating to hair loss syndrome, which demonstrates that the condition is not necessarily fatal, Coblentz said. But the weather was mild last winter and the deer were fed high-nutrition food that wouldn't be available in the wild, he added.
"I think most biologists agree it is the combination of hair loss syndrome with rugged winters and lack of nutrition that provides the biggest threat to the deer."
Diagnosing hair loss syndrome isn't necessarily straightforward, according to Rob Bildfell, a veterinary pathologist at OSU who handles wildlife cases for the university's Veterinary Diagnostic Lab.
"We have examined a couple of mule deer from The Dalles area that had damaged hair over the rump area, but it wasn't the same pattern of hair loss seen in blacktails," Bildfell said. "Nor have we found the exotic lice on the east side of the Cascades."
Coblentz said that now the lice are here, the best bet may be for deer to build immunity. "In a controlled setting, you can give the deer baths and dips to kill the lice," he said. "Eradicating the lice in the wild? Not a chance."
Bruce Coblentz, 541-737-1959