University of Wisconsin-Madison researchers have received a $2.4 million Department of Defense grant to study the behavior and persistence in soils of the agent believed to cause chronic wasting disease, and to determine CWD”s potential for spreading to other species.
Scientists already have circumstantial evidence of environmental reservoirs of prions for CWD and scrapie (a similar disease of sheep), according to Joel Pedersen, a soil scientist at the UW-Madison”s College of Agricultural and Life Sciences. ” We don”t know exactly how CWD spreads, but the environment may be involved in transmission between animals, and fields contaminated with prions could be infecting healthy animals,” he says.
Pedersen will examine how prions associate with soil components, and how soil composition could influence prion behavior. In a series of laboratory experiments, he hopes to determine the degree to which prions associate with typical soil components, such as clays, sand, organic matter and iron oxides. The work should show whether prions that adhere to soil components retain their infectivity, and whether association with soil components protects the prion from microbial degradation.
Results from these trials should reveal which soil types are more likely to maintain infective prions over long periods, how prions move through different soils, and which soils might allow prion-laden runoff into surface waters. The results may also show that prions associated with certain soil components are more likely than others to infect deer.
The CWD intensive harvest zone around Mt. Horeb – the area known to hold infected deer – covers about 260,000 acres. Most of those acres are woods and farmland – prime whitetail habitat. Deer infected with CWD may shed prions in their urine, feces or saliva. Infected whitetails that die on the landscape will contaminate the soil, potentially exposing many species, wild and domestic, to prions.
Pedersen points out that many animals ingest soil. Deer and other animals sometimes eat soil for its mineral content, and bucks may ingest soil while checking for does in heat. Sheep and other grazing animals consume soil when they uproot and eat plants.
Judd Aiken, a professor of animal health and biomedical sciences at the UW-Madison School of Veterinary Medicine, will study the potential for transmission of CWD to other species, both through carcass contact and soil contamination.
Aiken will test CWD isolates obtained from naturally infected deer. Deer that are genetically different also have distinct prion proteins, he points out, and these distinct proteins may have distinct characteristics – such as interspecies transmission.
The transmission of CWD to a new species could have severe consequences, including the ability to transmit to other new hosts. For example, CWD that infects elk and deer does not appear to be transmissible to cattle, yet the prions produced in the new host species may have a different host range – one that includes cattle.
A related study, funded by a five-year, $2.3 million NPRP grant, builds upon earlier UW-Madison work to characterize the biology of CWD and an animal”s genetic susceptibility to the disease. Led by Debbie McKenzie, a scientist in Aiken”s lab, researchers will work with tissue samples taken from both infected and uninfected deer to identify differences in the prion protein gene. “Different forms of the prion protein have different characteristics,” explains McKenzie. These differences can alter the disease”s incubation period, its clinical signs and its ability to spread to other animals and even jump the species barrier.