Chronic wasting disease research shows potential for human infection

New research into chronic wasting disease (CWD) by a team from the University of Calgary shows it has the potential to cross the species barrier from deer to humans.

CWD is caused by prions — a form of misshapen protein that can trigger the fatal degenerative neurological condition.

“We show that there is some potential of CWD prions to cross the barrier to humans,” said Dr. Sabine Gilch, an associate professor at U of C's faculty of veterinary medicine and the Canada research chair in prion diseases.

“We cannot predict that it happens (in the real world), but the potential is there.”

Albertans consumed the meat of roughly 70,000 deer last year.

 

Click for more info: 2021 provincial CWD testing report

 

Of 10,909 cervids (deer, elk and moose) tested by the province, 1,156 tested positive for the disease.

The large majority of those were Mule deer. Eight were elk. No moose tested positive.

The peer-reviewed research paper was recently published in the journal Acta Neuropathologica. Lead author Samia Hannaoui was in Germany this week presenting the findings at a prion disease conference.

Using transgenic humanized mice, which mimic the response of human bodies, researchers injected CWD prions directly into the brains of the mice.

“The majority of those mice developed a clinical prion disease, so they got sick from this injection,” Gilch said.

 

Click for more info: The research paper from the University of Calgary

 

But there were further surprises, some of which are encouraging.

It took the infected mice two to three times longer to develop symptoms.

“Even though there is potential to transmit to humans, the barrier is really high. So it’s not a very efficient process, I would say,” Gilch said.

The peer-reviewed research did not look at whether mice could be infected under real-world conditions, where an unknown critical load of prions would have to be ingested and pass through the digestive tract and on to the brain.

There were two concerning findings as well.

“Despite the clinical disease, it was very difficult to confirm the disease with the diagnostic tests that are currently used for diagnosing prion diseases in humans,” Gilch said, adding that doctors examining patients with an apparent prion disease will need to not only test for CWD specifically, but may need to use improved testing procedures.

CWD has never been detected in humans, but the findings suggest that may be a function of long periods before symptoms appear, inadequate testing and the difficulty in triggering an infection under real-world conditions.

 

Click for more info: Data on the dose required to trigger infection

 

The final surprise was the presence of infectious prions in the mouse faeces.

"This is really something that has not been shown before for any human prion disease and also not for this specific mouse model, and it's something that really concerns us,” Gilch said.

The finding is significant because it shows that human-to-human spread would be possible, although modern hygiene may make that highly unlikely.

For people who may eat wild venison, the research doesn't change handling or consumption recommendations — have cervids tested for CWD, label meat, avoid handling brain or spinal tissue and don't eat meat from an infected animal.

While the law generally requires all edible portions of hunted animals to be eaten, CWD-positive animals are explicitly exempt.