Chronic
wasting disease research becomes more crucial as cases grow in Pa. deer, Penn
State researchers hunt for answers to help limit CWD's spread.
UNIVERSITY
PARK, Pa, — The recent announcement by the Pennsylvania Game Commission that it
found 25 more wild deer with chronic wasting disease last year underlines the
importance of studies being conducted by a team of researchers in Penn State's
College of Agricultural Sciences.
With the
overarching goal of determining how the always-fatal-to-cervids disease will
disburse through the state's free-ranging white-tailed deer herd, the research
is aimed at informing the commission's efforts to slow or limit the spread of
the disease, according to David Walter, adjunct assistant professor of wildlife
ecology.
Chronic wasting disease infects the brain and nervous system of cervids, and animals cannot be tested while they are alive. Here, researcher Will Miller (left) samples a deer head for the disease. |
Often
referred to as CWD, chronic wasting disease infects the brain and nervous
system of cervids. The illness, which belongs to a group of diseases known as
transmissible spongiform encephalopathies, or prion diseases, eventually
produces enough damage to the brains of affected animals to result in death.
While CWD is similar to so-called mad cow disease in cattle and scrapie in
sheep, there is no known relationship between them.
There is no
strong evidence, either, that humans can contract CWD, according to the U.S.
Centers for Disease Control and Prevention, although the disease is similar to
Creutzfeldt-Jakob disease, a rare, fatal syndrome that afflicts people.
Walter, who
is assistant unit leader of the Pennsylvania Cooperative Fish and Wildlife
Research Unit at Penn State, conducted research from 2007 to 2011 on the spread
of the disease in Colorado and Nebraska in free-ranging mule deer and
white-tailed deer. Since coming to Penn State in 2012, he has concentrated on
the CWD outbreak spreading through deer herds in Virginia, West Virginia,
Maryland and Pennsylvania.
Working
under Walter's guidance in 2013-14, master's degree student Tyler Evans, now a
wildlife biologist with the West Virginia Department of Natural Resources,
investigated the geographic coordinates where deer testing positive for CWD
were found, and he modeled the likely future spread of the disease in
Pennsylvania.
"That
research looked at what environmental variables were associated with the
presence or absence of chronic wasting disease in the Northeast," Walter
said. "We obtained the geographic coordinates of hunter-killed deer that
tested positive for CWD and overlaid them on a map showing a variety of habitat
and landscape features. The analysis showed a high prevalence of CWD in deer
sampled from low-lying open and developed landscapes."
Testing road-killed deer for chronic wasting disease has revealed that not just older deer are affected. Most of the road-killed deer tested in Pennsylvania have been yearling males and females. |
Now,
Walter's advisee Will Miller, a doctoral degree candidate in the Intercollege
Graduate Degree Program in Ecology, is continuing to study the spread of CWD in
Pennsylvania. But he is focusing on whether some deer might be susceptible to
the disease because of their genes, and how genetic variation in deer might
influence where and how fast the disease spreads.
"It
appears that deer in Pennsylvania's Northern Tier are less related to those in
Maryland and in southern Pennsylvania," Walter said. "That may well
have implications for how CWD spreads."
Walter and
Miller are slated to travel to Edinburgh, Scotland, in late May to attend an
international conference focused on prions and diseases the mysterious proteins
cause. At the conference, Miller will present findings of his research focusing
on genetic susceptibility of some deer in Pennsylvania to chronic wasting
disease.
Detected in
captive and free-ranging deer and elk in 23 states and two Canadian provinces,
CWD was found last year in reindeer in Norway, Walter pointed out. "The
Europeans are eager to learn what we know about the disease, based on our
experience in North America," he said. "But despite all that we are
learning about the disease, there is much we still don't know."
In the case
of the outbreak in Pennsylvania's wild deer, that includes how the disease
infected free-ranging deer in Pennsylvania. Among the possible sources, two
include captive deer and wild deer moving from Maryland. Although researchers
have seen evidence that deer may carry the disease over the border with
Maryland, the Pennsylvania counties of Blair and Bedford, where CWD originally
was found in 2012, also had the highest inventories of captive cervids in Pennsylvania.
The location
of the original outbreak, which was more than 40 miles from the Maryland
border, makes it difficult to confirm the actual source of infection.
"In
southern Fulton and Bedford counties, we have seen more CWD-positive deer along
the border," Walter said. "We have seen over time that it is likely
the disease is moving into this area from the West Virginia-Maryland
outbreak."
The Game
Commission tests both hunter-killed deer and animals killed on highways in
parts of the state for CWD to assess the dimensions of the outbreak, Walter
noted. The dual approach addresses sampling bias built into testing hunter
harvests.
Because
hunters are restricted by antler regulations from killing young male deer, and
they mostly pass on taking young females and button bucks, some reached the
mistaken conclusion that the disease primarily infects older deer. But road
kills show that is not the case, Walter explained.
"It is
a chronic disease, so it takes a while for the animal to succumb, but there is
a fallacy out there that young deer can't get it — but they do, and we are
detecting it now. Wisconsin has found CWD in fawns," he said.
"Most
of the road kills with CWD are yearling males and females. We don't see that in
hunter harvests, so our data from across the country has been skewed.
Collecting and testing road kills has been a great investment of resources, and
it has proved to be very valuable in finding this disease in areas we wouldn't
find it otherwise."
Chronic
wasting disease is not established in Pennsylvania yet, the way it is in
Wisconsin and West Virginia, Walter believes, and he would like to see the Game
Commission and state Department of Agriculture take steps, such as targeted
culling of deer in CWD hotspots, to keep it at bay.
By Jeff
Mulhollem
May 23, 2017