North-eastern deer more susceptible to decay disease than the western one

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In the last decade or so, David Walter's research group in the College of Agricultural Sciences has studied how the movement, behavior and genetics of wild deer are influencing the spread of chronic wasting disease.

Image: Joe Kosack / Pennsylvania Game Commission

Some deer are more susceptible to chronic wasting disease that is spreading through white-tailed herds in much of the United States, according to researchers at Penn State, who have identified a group of genetic markers that reliably predict which animals they are more vulnerable to the contagious neurological disorder.

"The genetic variants that would make deer less susceptible to chronic wasting disease are much lower in the East, probably because they were not necessary," he said. David Walter, assistant professor added wildlife ecology. "For a long period of time, their survival could have been somehow favored by losing these genotypes. They were not important until a disease like chronic wasting disease appeared. We saw that deer with the most sensitive genotypes they are in the majority. "

In the last decade or so, Walter's research group in the College of Agricultural Sciences has studied how the movement, behavior and genetics of wild deer are influencing the spread of chronic wasting disease. Often referred to as CWD, it is a fatal prion disease that affects the deer family and belongs to a group of similar diseases, such as mad cow disease and scrapie in sheep, called transmissible spongiform encephalopathies.

After testing over 2,200 deer killed by hunters in Virginia, West Virginia, Maryland and Pennsylvania, researchers identified 11 different subpopulations of deer in the Mid-Atlantic region where an epidemic of chronic decay is occurring. The researchers used over 700 Pennsylvania deer DNA samples to assess genetic susceptibility to the disease in subpopulations, and these results were published at the start of this year in the Prion journal.


doe and fawn

In the United States, chronic wasting disease spreads differently in the East than in the West, because the numbers and density of deer are much higher in the East, according to the researchers, who are trying to unravel the genetic nuances to understand where the disease may show up.

IMAGE: Pennsylvania Game Commission

"Deer in the Mid-Atlantic region has a higher percentage of the CWD-sensitive genotypes than the west deer populations that have been tested in other states," Walter said.

He noted that the disease was first observed in the mule deer in Colorado in 1967 and has been spreading eastward across the continent since. It now infects deer and elk in 24 states and several Canadian provinces, and was found in reindeer, moose and red deer in three Scandinavian countries.

"In the United States, CWD diffuses differently in the East than in the West, because the numbers and densities of deer are much higher in the East," said Walter, assistant unit leader of the Pennsylvania Cooperative Fish and Wildlife Research Unit of Pennsylvania. "We have tried to unravel the genetic nuances to understand where a chronic wasting disease is likely to manifest."

In previous published studies, Walter and colleagues determined that geographical features such as rivers, mountain ranges and high ridges have channeled the spread of CWD in the East. Even the characteristics created by man, like motorways, seem to have influenced the movement of deer, driving where CWD was found in deer.

The latest research by the Walter group consolidates the numerous genetic resources for white-tailed deer in a manageable panel of 11 genetic markers to provide a uniform methodology that is able to improve genetic comparisons. The researchers examined the "microsatellite" panels of 58 previous or ongoing studies on cervids in CWD outbreaks in other regions.

In the findings published today (June 6) on BMC Genetics, they describe a protocol to differentiate cervical subpopulations and evaluate their efficacy using 720 hawthorn DNA samples in the Mid-Atlantic region. In the study, the researchers analyzed 2,200 cervical specimens in four states to evaluate microsatellites.

"The 11 markers we have selected are easy to interpret and are able to provide a common platform for future genetic studies such as those for CWD," said lead researcher William Miller, a former Penn State doctoral student, now an assistant professor. of biology at Calvin College in Michigan.

Miller pointed out that many genetic studies conducted previously used several sets of genetic markers.

"We wanted a main panel that was widely useful and effective in the range of white-tailed deer, and we included many of the markers that were used in the studies of the Midwest and West states," said Miller. "This panel includes markers that can be useful for evaluating genetic models."

Follow-on studies almost completed by Miller and Walter's laboratory describe a genetic method to determine when a CWD-positive deer is discovered, where it comes from and whether it is a wild or bred in captivity. This information will guide the reaction of wildlife managers to the discovery, as they decide whether to set up areas for the management of disease and targeted removal of deer to slow the spread of CWD.


Walter Miller

William Miller tests DNA samples collected from white-tailed deer in the Mid-Atlantic region.

Also involved in the research were Jessie Edson, head of the genetics laboratory in Department of Ecosystem Sciences and Management; and Peter Pietrandrea, university researcher, e Cassandra Miller-Butterworth, assistant professor of biology, both a Penn State Beaver.

The Pennsylvania Game Commission, the Maryland Department of Natural Resources and the Virginia Department of Game and Inland Fisheries supported this research.

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