New Brunswick

How researchers are tracking down N.B.'s mystery neurological disease

Expert investigators are working to find out what caused the 43 cases. First, they say, you have to find out what didn't.

What caused the cluster of 43 cases? First, experts say, you have to know what didn't cause it

Experts are looking at environmental toxins as a possible cause for New Brunswick's mystery neurological disease, as well as the possibility that this is a new variant of a prion disease — or a new disease entirely. (Stefan Wermuth/Reuters file photo)

The news last week that an unknown neurological disease has been identified and found only in New Brunswick has sparked reaction and headlines across the country.

But it has also attracted the attention of a growing team of scientists, researchers, neurologists and other experts who are on the case, both at the provincial and federal level.

The disease is a mystery so far. Forty-three cases have been identified since 2015. Thirty-five of them are on the Acadian Peninsula in the province's northeast, and eight are in the Moncton area in the southeast.

It has symptoms similar to Creutzfeldt-Jakob disease, known as CJD, a rare and fatal brain disease, but testing has so far ruled out CJD and other known prion diseases, according to a Public Health memo sent to doctors earlier this month.

Experts are now looking closely at environmental toxins as a possible cause, as well as the possibility that this is a new variant of a prion disease — or a new disease entirely. 

Anxious residents, particularly in the affected areas, are clamouring for answers. So how, exactly, will researchers suss out, narrow down and finally identify the cause of the disease?

Michael Coulthart, the senior scientist heading up the federal research teams, said there's a "fairly typical sequence of stages" that disease cluster investigations go through.

It begins, he said, with identifying as precisely as possible what it is you're looking at.

The National Microbiology Lab is Canada's only biosafety level-4 lab, located in Winnipeg. (Trevor Lyons/CBC)

Looking for possible common causes

"The very first thing that needs to be done is to carefully characterize what people are thinking is the same disease," said Coulthart, who heads the federal Public Health Agency's Creutzfeldt-Jakob Disease Surveillance System out of Ottawa.

"If thorough diagnostic investigation indicates that you're looking at an unexpectedly high number of the same thing, however you define that … then you start looking for possible common causes."

Coulthart said researchers have begun that work, but the challenge in getting "the full characterization" of a neurological disease is that it typically requires a post-mortem examination.

Of the 43 cases, he said, five people have died, and autopsies have been conducted on three of them.

"So we've only been able to go part of the way in the direction of establishing the common features the patients in this cluster have," Coulthart said.

But with the assumption that the similarities between the patients suggest a common cause should be investigated, "you then start looking at the diagnostic results that you have."

In this case, the information that's been gathered is extensive.

Moncton neurologist Dr. Alier Marrero is heading the investigation of the disease cluster here in New Brunswick. (Tori Weldon/CBC)

Deep questionnaires, dozens of tests

Dr. Alier Marrero, the Moncton neurologist who is leading New Brunswick's research of the cluster, said that to be included in the cluster, patients first have to have had other possible conditions ruled out.

Detailed evidence is collected via clinical exam and "deep questionnaires" about lifestyles, travel, surgery, professions, place of residence and more.

Toxicology tests, brain and body imaging, metabolic tests, genetic testing, spinal taps are all conducted to rule out everything from lupus to autoimmune disorders to Lyme disease.

Next comes examination of the possibility that the patients have been exposed to a common risk factor. Given the fact that the cluster has been found in just two areas of the province so far, this is a leading hypothesis.

"But that can take an awful lot of time and effort," Coulthart said, noting that people are exposed to thousands if not millions of things that could be considered a risk for disease. 

This, he said, is where expertise of a multidisciplinary sort becomes essential. 

That's precisely what the team being co-led by the Public Health Agency and the Province of New Brunswick has been tapping into for the past couple of months.

How about this: Over the course of the investigation, teams have consulted with infectious disease experts, neurologists, environmental health groups, epidemiologists, veterinarians and experts in public health both in New Brunswick and across Canada.

Once you've narrowed the list of possible causes down, "you can look in a more focused way at possible common environmental exposures and set about testing."

"And that's where we are right now," Coulthart said.

Both Coulthart and Marrero stressed that it's a deeply involved, complex and time-consuming process.

"It will take time," Marrero said.

How much time?

Obviously no one can be certain, but Marrero said it's encouraging that "momentum is building," with expertise being volunteered here at home and from around the world and vast amounts of data compiled.

"I'm optimistic by nature," Marrero said. "But I hope it would be a matter of a few months to a year." 

N.B.'s mystery disease: What we know so far

What is it?

  • An unknown neurological disease with similarities to Creutzfeldt-Jakob disease, a rare and fatal brain disease

When was it discovered?

  • The first occurrence was retroactively found to have occurred in 2015, when the possible existence of a cluster of disease was first recognized by the CJD Surveillance System at the Public Health Agency of Canada in 2020. In 2019, 11 additional cases were identified, with 24 more cases in 2020 and another six in 2021.

When was it made public?

  • A March 5 internal memo from Public Health to health-care professionals was obtained by Radio-Canada and reported by Radio-Canada and CBC News on Wednesday, March 17.

Where are the cases?

  • The disease has so far only been identified in New Brunswick. It appears to be concentrated on the Acadian Peninsula in northeast New Brunswick and the Moncton region in the southeast. 

How many cases are there?

  • Forty-three cases have been identified. Of those, 35 are on the Acadian Peninsula and eight are in the Moncton region. 

Who has been affected?

  • The disease affects all age groups and affects males and females equally, according to the Public Health memo. About half of the affected individuals are between 50 and 69 years of age.

What are the symptoms?

  • Symptoms include changes in behaviour, sleep disturbances, unexplained pain, visual hallucinations, co-ordination problems and severe muscle and brain atrophy.

Is it contagious?

  • Because the cause has not been determined, it is not yet known whether the disease is contagious.

What are the possible causes being researched?

  • Despite many similarities, tests for Creutzfeldt-Jakob disease have so far ruled out known prion diseases.
  • Scientists are currently looking into the possibility that this is a new variant of a prion disease — or a new disease entirely.
  • Neurologists and scientists suspect the cause might be exposure to an as-yet-undetermined environmental toxin.   

Who's researching it?

  • The disease is the subject of investigation by an all-Canadian team of neurologists, epidemiologists, scientists, researchers and other experts.
  • Here in New Brunswick, Moncton neurologist Dr. Alier Marrero is leading the research. In Ottawa, senior scientist and Creutzfeldt-Jakob Disease Surveillance System director Michael Coulthart is leading the research.  


  • This story has been updated from an earlier version to reflect that the Creutzfeldt-Jakob Surveillance System clarified on April 7 that the 2015 case wasn't identified that year, but retroactively in 2020.
    Apr 07, 2021 12:18 PM AT


Marie Sutherland is a web writer with CBC News based in Saint John. You can reach her at


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