Is chronic wasting disease (CWD) a potential time bomb for the agriculture industry? There is no direct proof of CWD transmission via contaminated grain or feedstuffs, but researchers say evidence warrants a closer look at the possibility.
On average whitetail deer have a two-year CWD incubation period from infection to death. Although deer appear and act healthy for the majority of the disease duration, they can transmit CWD nearly the entire span. Deer contract CWD through infectious saliva, feces and urine, or via soil ingestion, foraging or a contaminated water source.
There are no known cases of natural transmission of CWD to domestic livestock. However, in a lab, CWD has been reproduced in cattle and swine, and research studies continue to examine crossover possibilities.
“The question is: If CWD is able to get into livestock or swine, could it be transmitted in feedstuffs?” says David Clausen, a retired Wisconsin veterinarian, farmer and former chair of the Wisconsin Natural Resources Board. Clausen serves as board president of Midwest Environmental Advocates.
“There isn’t enough science, but it’s been shown plants can pick up proteins in the soil matrix through roots and deposit them in shoots and leaves, likely in flowers as well,” says Bryan Richards, CWD project leader for the U.S. Geological Survey National Wildlife Health Center in Madison, Wis. “Is the infectivity still there, and is the concentration enough to transmit disease?”
Uptake in a laboratory isn’t real-world confirmation, but Richards finds the implications disturbing. “With the geographic footprint of CWD greatly expanded, we have to ask if plant material really moves infectious material,” he says.
Take a county with a 40% CWD rate in a whitetail population. If 20 deer feed in-and-out of a given wheat field, eight are CWD positive. An adult deer defecates 12 times per day and urinates more. After harvest, if the wheat straw is baled, statistical probability places a good deal of fecal material in the bales.
Tracy Nichols, a molecular biologist and staff officer with USDA’s Veterinary Services Cervid Health Program in Fort Collins, Colo., cites studies where plant roots grown in hydroponic or spiked soil solutions were exposed to CWD material. The stem and leaf tissue subsequently tested positive for infected prions.
“There is no scientific conclusion, but the questions raised could impact international trade. Right now, we don’t know what, if any, threat exists,” she says.