Chronic wasting disease hasn’t yet snuck past the Idaho-Oregon border, and scientists are concerned about how it will impact the state’s rare Columbian white-tailed deer.
“We think they’re basically sitting ducks for chronic wasting disease,” said Al Roca, a professor of animal sciences at the University of Illinois Urbana-Champaign.
Various deer and elk have genes that have been associated with a lower occurrence of chronic wasting disease (CWD), but Columbian white-tailed deer do not appear to have these genes. Still, once infected, all cervid species ultimately die from CWD.
But new research reveals that elk in the region with advantageous versions of a certain gene may slow the spread of the deadly illness, which may help shield these more vulnerable deer.
Natural protection
Since its discovery in 1967, experts have found CWD in free-ranging cervids in 36 U.S. states and four Canadian provinces. A misfolding in the prion protein causes the fatal, highly contagious disease. While scientists don’t know exactly the purpose that healthy prions serve, they are distributed throughout the body and are especially concentrated in the brain and central nervous system. When a healthy cervid comes in contact with a misfolded prion, its own prions begin to change shape as well. “That leads to a runaway misfolding reaction,” Roca said. “It’s a very unusual disease.”
But cervids with a certain genetic variations in the prion gene appear to have a lower incidence of CWD and live longer with the disease. This is caused by just one change in an element of the animal’s genetic code, called a single nucleotide polymorphism (SNP). The SNPs rewrite the genetic code, sometimes yielding a slightly different prion protein. Scientists think that the prion protein can still function properly but is less likely to misfold when it comes in contact with an infectious prion. “Those SNPs can change how likely the animal is to get CWD,” said Yasuko Ishida, a research scientist also at the University of Illinois Urbana-Champaign and lead author on the study.
Slowing the spread?
In a new study published in the Journal of Heredity, Ishida, Roca and their colleagues studied the genetics of Rocky Mountain (Cervus canadensis nelsoni) and Roosevelt elk (C. canadensis roosevelti). A little less than half of Oregon’s elk carry the advantageous variant, which is a high percentage compared to elk populations nationwide.
Researchers found that 49% of Rocky Mountain elk and 42% of Roosevelt elk carried at least one copy of the advantageous gene. The prevalence of advantageous SNPs in Oregon was relatively high compared to other populations, “but not likely high enough to keep CWD from spreading once it’s introduced,” Roca said. “Half the animals are still quite vulnerable to CWD.” The study also provides a baseline to track the prevalence of the advantageous prion gene if CWD ever gets introduced into the state.
While these genes don’t make the animals fully resistant, the incubation period is longer. And CWD hasn’t been detected in Columbian white-tailed deer (Odocoileus virginianus leucurus), which were once federally endangered but are now listed as threatened and live in western Oregon and Washington. But the subspecies is entirely genetically susceptible. The elk that are genetically fortified and live in the area might still buy the subspecies time, taking longer to pass the disease from the Idaho border to the western edge of the state where the rare deer live. However, because these elk also seem to live longer once they’re infected, they could be even more dangerous to other wild cervids by shedding infectious material longer in areas that Columbian white-tailed deer occupy.
Researchers have also been looking into other white-tailed deer subspecies, like Key deer (Odocoileus virginianus clavium) in Florida. Unlike the Columbian subspecies, Key deer have high rates of the advantageous genes. “Depending on the population, the frequency of SNPs are very different,” Ishida said.
In terms of keeping CWD out of Oregon, Ishida said the disease is difficult to control, but there are a few things people can do, like not translocating deer or elk from other states or infected areas.
Article by Olivia Milloway
