A third case of chronic wasting disease (CWD) in 2019 has been confirmed at a Canadian deer farm, but the Canadian Food Inspection Agency says no infected meat from this year's cases has been allowed to enter the country's food supply.

All the cases of CWD, a fatal nervous system disease related to mad cow disease that infects deer, elk, moose and caribou, have been located in Alberta.

The latest case was confirmed on July 26 at a white-tailed deer farm, according to the Canadian Food Inspection Agency.

Last year, thousands of deer from an infected farm in Quebec were released for human consumption.

Even a single transfer to a person — proving that humans are susceptible — would bring catastrophic consequences. ​ — Letter on behalf of CWD researchers

CBC News asked the CFIA for details about the latest infected case and whether meat from that herd has been allowed to enter the country's food supply.

The agency responded after this article's publication to say no meat from any deer or elk herds has entered the human food chain.

The CFIA said the deer from the two recent CWD-confirmed deer herds were humanely destroyed, and that no meat from a CWD-positive elk herd that tested positive for the disease in February was allowed to enter the food system.

The agency said it's working to prevent the spread of the disease from the infected deer herds.

"Both premises remain under quarantine at this time and disease response activities have been initiated," the agency said.

CBC News has followed up to inquire if elk that did not test positive for CWD, but were part of the infected herd, were allowed to enter the food supply.

Advocates are calling for the names of the infected farms to be released and for stricter controls to manage the disease.

"The public has a right to know, if you know these deer farms or elk farms are testing positive," said Kat Lanteigne, executive director of BloodWatch, a non-profit that advocates for a safe blood donation supply. "Do you want to have a venison steak from a CWD-contaminated farm?"

The CFIA's website recommends meat from an infected animal not be consumed.

Though there's no direct evidence so far that CWD has been transmitted to a human, recent research shows the disease can be transmitted to non-human primates and indicates the disease is evolving.

Animals that test negative or are under a year old from a CWD-infected herd can be sold for food in Canada — but the CFIA's website states a negative test doesn't guarantee an animal isn't infected.

Lanteigne and more than 30 doctors, researchers and advocates signed a letter in June asking federal ministers to take urgent action to limit the spread of what they describe as an epidemic.

"While no human cases of CWD have been confirmed, scientists note that while low, the risk is not zero — and it is evolving. Evidence suggests that CWD conversion is more adaptive than bovine spongiform encephalopathy [mad cow disease], and following efficient transfer to a second species of non-human primates, Health Canada advised that 'CWD has the potential to infect humans,'" the letter reads.

"Thousands of CWD-infected animals are being consumed by hunters and their families across North America every year. Even a single transfer to a person — proving that humans are susceptible — would bring catastrophic consequences with limited options."

Mad cow initially not linked to humans

Lanteigne points to mad cow disease, which initially wasn't believed to be transmissible to humans — and was later found to be linked to variant Creutzfeldt-Jakob disease, a fatal brain disorder in humans.

Major outbreaks ravaged the U.K., killing dozens — three of whom died from blood donations that had been tainted.

Canadians are still deferred from donating blood if they spent three or more months in the U.K. between 1980 and 1996.

"When [mad cow] broke out in the U.K. they didn't think it would make the jump to human beings.… Ten years later they discovered that not to be true and it had a huge impact on their plasma supply," Lanteigne said.

"When it comes to prion diseases we are extremely concerned because you have to take a precautionary approach to keeping human beings and the blood supply safe."

'A serious issue'

"It's a serious issue," said Dr. Michael T. Osterholm, an infectious disease expert based in the U.S. and another signatory on the letter.

He fears that like mad cow, CWD could have an incubation period of more than a decade — meaning if a human has been infected with a recently evolved strain, it may not be known for years.

"We're seeing a substantial increase in transmission" in animals in the deer family, said Osterholm. "Studies that were done even five to seven years ago apparently demonstrated it was unlikely that certain strains were going to infect humans. You can't say that anymore … we now have enough evidence to say that it maybe is possible."

He also said the prions — misfolded proteins that transmit the disease — have been found in the meat of the deer, unlike mad cow where the prions are found primarily in the central nervous system, possibly increasing the risk of transmission to those who eat venison.

Moose meat is pictured in this file photo. Health agencies say not to eat meat from animals that have been infected with chronic wasting disease. (Christina Jung/CBC)

Some regions have implemented steps to try to prevent the disease from spreading.

Last week, B.C. implemented a mandatory sampling program that requires hunters to submit heads of deer in the Kootenay region for testing, after five animals with the disease were found in neighbouring Montana.

In the U.S., responses are even more strict — the Department of Agriculture will buy infected herds and destroy every animal to maintain quarantine.

Osterholm and Lanteigne say much more needs to be done across Canada to prevent human exposure, and the country must develop a preparedness plan in case it's too late.

"We're not trying to say the house is on fire. We're saying you don't light a match … if a human case happens, that means it is out, and it's out everywhere. That would mean you have literally tens of thousands of asymptomatic [blood] donors walking around," Lanteigne said.