Natures response to the disease?
Genotypes make a difference
Researchers have found that deer with different genes react differently to CWD exposure. The key gene at a location known as codon 225 can have one of three combinations of alleles respectively named SS, SF or FF, DeVivo said. All three are represented in the Converse herd.
If the DNR wants $1.5 million for CWD testing, will we spend some researching answers, or will it all be spent monitoring and killing deer.
The majority of mule deer today are SS, and they get infected at a higher rate, the study showed. “They are 30 times more likely to be CWD-positive compared to deer that had SF or FF,” she said.
Only one of 29 mule deer of the SF genotype turned up CWD positive. FF deer are rare — only two of the 143 captured had that genotype. Neither was infected with CWD.
Although DeVivo’s mathematical model predicted the herd would go extinct in 41 years, without accounting for genetic variations, that won’t actually happen because new deer are expected to move into the herd’s home range. When accounting for genetic variation, the study predicts the genetic mix of a surviving population will change over time.
“What I found was within a 100-year period we do see a significant increase in those less-susceptible genotype — where the FF becomes the dominant genotype,” she said. “I still model a significant decline in the population.”
What scientists don’t know is whether the FF genotype is rare because it also carries a disadvantage. For example, suppose FF does were somehow unattractive to bucks or turned out to be bad mothers.
“That’s the debate right now,” she said. “Just because it’s rare does not mean [it is] some adverse genotype. Since there was no selective pressure on it ’til now, it’s just a rare genotype.”
Her study captured two FF does, but data on them spans only one year, and the small sample size precludes scientific conclusions.
“They were not positive [for CWD,] they both were pregnant and they both recruited fawns,” she said. “It seemed like they were just as fit as any other deer in the population.”
Does this research translate from deer to elk?
DeVivo’s research doesn’t translate easily to elk. “We know they [elk] are very susceptible,” she said. But wild elk in Wyoming have not been decimated in the same way as Converse deer.
“For some reason in free-ranging populations [of elk] we just don’t see the same thing we see in captivity,” DeVivo said. “I don’t know if anyone knows why that is.”
One modeling study published last year predicted severe declines among feedground elk in Sublette County, even after hunting seasons are modified in the face of infection. That conclusion took into account an apparent difference in susceptibility among elk of three different genotypes.
Like the deer, elk are classified into three genotypes when considering their sensitivity to CWD, said Brant Schumaker, assistant professor at the University of Wyoming Department of Veterinary Sciences. About 70 percent in a herd are MM genotype elk and most susceptible. Most of the rest are ML genotypes and live slightly longer. The only LL elk in a decade-long Wyoming experiment hasn’t become infected. LL elk make up approximately 2 percent of a normal population.
In a 10-year experiment Schumaker took part in, Wyoming Game and Fish captured a band of 39 elk in Jackson Hole in 2002, relocated them to a southeast Wyoming facility, and exposed them to CWD. In 10 years, all the other elk in the group contracted CWD from infected pens and withered away at the Tom Thorne/Beth Williams Wildlife Research Center at Sybille.
But not the lone LL elk. Her ear tag is No. 12, but researchers nicknamed her Lucky. She’s had a calf, and doesn’t look sick or test positive for CWD.
Meet ‘Lucky’, the lone survivor of a CWD elk study in Wyoming who carries the rarest genotype. Is she resistant or immune to CWD?
Lucky, the 600 pound elk, has not caught CWD despite 13 years of exposure to the disease in a Game and Fish Department wildlife lab. Her rare genotype may make her resistant to the disease, possibly even immune. (Terry Kreeger/Wyoming Game and Fish Department)
“She is, if anything, overweight,” Schumaker said. “My understanding is that she’s kind of a pill from the caretakers’ perspective. She stands up for herself.”
Is Lucky the 600 lb. elk immune to CWD? Will Lucky’s LL cousins become the mothers of all future Wyoming elk once CWD runs its course? Does the LL genotype also carry some disadvantage scientists don’t know about?
Even once Lucky dies and is autopsied, Schumaker said, researchers won’t know for sure whether she is immune. A new experiment would be necessary to determine that.