Symptoms seemingly straight out of a horror movie have been plaguing individuals, with some experiencing the sensation of insects crawling beneath their skin or being tormented by terrifying hallucinations of the deceased.

Others have been afflicted by such severe muscle spasms that sharing a bed with their partner became impossible, or suffered memory lapses so significant they couldn’t recall their location or even the simplest words.

One man was so bewildered that he failed to recognize the woman sitting in his living room, only to realize hours later she was his wife. Some have fallen into the grip of Capgras delusion, convinced their loved ones had been replaced by identical impostors.

Over the past seven years, around 500 individuals in New Brunswick, a small Canadian province with a population of just 870,000, have been under the care of a single neurologist. They all suffer from this perplexing ‘mystery disease’ that continues to baffle experts.

The quest for answers has grown so desperate that one patient chose to utilize Canada’s comprehensive assisted suicide program, and another is contemplating the same decision.

This month, the provincial government is set to unveil the results of a much-anticipated investigation into this complex saga. The situation has transcended mental health issues, inciting accusations of gross medical negligence, political misconduct, alleged corporate environmental pollution cover-ups, and the heartless neglect of patients enduring daily suffering.

Moncton – the province’s biggest city and the hub of the controversy – hardly seems like a hotbed of intrigue. This week, when the Daily Mail visited, it found empty streets and a typically comatose Canadian community hunkered down for a hard winter.

The story that drew attention here goes back to 2018 when Laurie Beatty, an 81-year-old retired builder, started acting strangely over Christmas. He told his wife the year was, in fact, 1992 and expressed puzzlement as to why he had white hair. He started having seizures and, by the end of May, was dead.

A post-mortem indicated Beatty had contracted Creutzfeldt-Jakob Disease (CJD), an extremely rare and serious brain condition which is related to Mad Cow Disease.

A few months later, the dead man’s neurologist, the Cuban-born Dr Alier Marrero, broke the news that the tests had come back negative for CJD.

‘There’s something going on,’ the family recalled him saying. ‘And I don’t know what it is.’

For Dr Marrero revealed that in the past four years he’d treated a ‘cluster’ of more than 20 patients for very similar symptoms to Beatty’s. Some had died as their muscles wasted away and their cognitive abilities collapsed.

Many were unusually young – some in their 20s. And all were impossible to diagnose definitively even after a battery of tests, including for CJD, said Dr Marrero.

He soon became convinced he was dealing with a previously undiagnosed neurological syndrome – and he wasn’t alone.

Other experts in his field – notably federal scientists at Canada’s Public Health Agency – took notice and set up a working group of experts to investigate.

Seven years on, at least 50 of Dr Marrero’s 500 patients have reportedly died while those who survive continue to battle against multifarious ailments whose cause remains fiercely disputed.

One of them, Mandy Maillet, 39, a married mother of two who lives in Turtle Creek, near Moncton, has been Dr Marrero’s patient since being referred by her doctor in 2022. Another neurologist had suspected she had multiple sclerosis but tests suggested otherwise.

Since 2019, Mandy, who was diagnosed with ovarian cancer last year, has been experiencing progressively more serious symptoms, such as frequent falls, muscle spasms, shooting pains, limb numbness, dizziness, vision problems and splitting headaches.

The falls have been so bad she had to have reconstructive surgery on her ankle. ‘I would just lose my balance – it was like the ground had to be perfectly flat,’ she told the Daily Mail, standing in the kitchen of her bungalow deep in one of the huge forests that cover much of the province.

Sometimes she will suddenly become confused and disorientated, or even angry. Her sensory perception has been completely messed up. ‘I get really strange sensations like someone is pouring water on my head,’ she said. At other times, she feels as if there are ‘creepy crawlies in my skin’.

She has to rely on her husband, Eric, who gave up his job in the military to become a delivery driver when she became ill, to do a lot of the cooking and housework, as it’s beyond her.

Sarah Nesbitt, another Marrero patient, is a former radio host who said it was ironic that she suddenly found herself lost for words, even simple ones – one of many symptoms she experienced.

A ‘strong woman’ who rarely had to see a doctor was transformed into a medical wreck in early 2020.

An outdoorsy type, she rapidly developed problems walking and started having seizures. ‘I had no control of my bowels or my bladder,’ she told the Daily Mail. ‘I was [being sick] every day for six months. A couple times I didn’t know who I was or where I was.’

On one occasion, she put her hand in the flame of a stove – unable, she said, to stop herself.

When news leaked in early 2021 that officials in New Brunswick had alerted doctors to what they called ‘New Brunswick neurological syndrome of unknown aetiology’, it made global headlines.

Dr Marrero was flooded with new cases while investigators followed up a torrent of theories.

Some speculated the condition may be caused by the Covid vaccine. Others said it could be the lingering effects of notorious defoliant Agent Orange on a local army base in the 1960s, the result of a moose-borne parasite or a ‘toxic algal bloom’. None has yet been proved.

The Canadian Institutes Of Health Research offered the cash-strapped province $5 million (£2.7 million) to pay for a two-year clinical investigation. The organisation’s boss congratulated Dr Marrero on uncovering ‘one of the most unusual constellations of findings I have ever seen’.

New Brunswick duly set up a specialist clinic to treat Dr Marrero’s patients and put him in charge. Just a month later, in May 2021, the New Brunswick government curiously got cold feet. It stopped collaborating with the federal government and, surprisingly, said it wouldn’t be taking up the offer of the $5 million to fund a more in-depth investigation.

Officials have never explained this odd – some say suspicious – decision, although insiders say they’d become concerned that Dr Marrero and the federal experts were too invested in making some great scientific discovery.

A few months later, Dr Marrero was removed from the new clinic – although most of his patients decided to stay with him.

Meanwhile, a neuropathologist named Dr Gerard Jansen, who had long been critical of Dr Marrero, was stirring up trouble, telling colleagues he was ‘flabbergasted’ by the scientific credibility of Dr Marrero’s notes on his patients.

While he didn’t deny people were suffering, Dr Jansen was suspicious at the way the neurologist tried to draw a connection between what he described last week as a ‘diarrhoea of symptoms’.

But sceptics sensed another, darker, reason why the province’s political leaders suddenly cooled on the charismatic, softly spoken Dr Marrero. He was arguing with ever greater intensity that environmental pollution was to blame.

He said the common factor among his patients was that their blood and urine contained unduly high levels of heavy metals such as mercury and a widely used, but controversial, herbicide called glyphosate. It has been banned in some countries – due to research which suggests it causes cancer – but is sold as a weedkiller in Britain under the name Roundup.

It’s the most widely used herbicide in Canada – particularly in deeply-forested New Brunswick, where it is also sprayed along power lines and at other utilities sites to stop trees growing.

Surely New Brunswick’s leaders would jump at the chance to clamp down on polluting companies?

Quite the opposite, some contend. They say the firms behind such contamination are powerful corporations, involved in oil, power and forestry. They’re not only major employers in New Brunswick, one of Canada’s poorest provinces, but have vast reserves to spend on any legal action. Plus, a reputation for having a toxic environment would not do much for New Brunswick’s vital tourist industry.

So this – according to a vocal alliance of environmental activists, Marrero patients and the neurologist himself – was a battle the politicians wanted to avoid.

Dr Marrero certainly believed he’d made himself a target of shadowy forces. According to patients and journalists, he became paranoid about eavesdroppers and even claimed he’d been followed once.

Yet his suggestion that there was an environmental cause behind his patients’ conditions is hardly an idea without foundation. Neurodegenerative diseases cause death and disability, but scientists struggle to understand them. And evidence has been building since the 1980s that toxic substances such as pesticides and herbicides may trigger neurological illnesses such as Parkinson’s and Alzheimer’s.

Dr Marrero noted that most of his patients came from two areas: in and around Moncton and the Acadian Peninsula, an underpopulated coastal region full of blueberry farms, charming fishing villages and beautiful beaches.

Further, Dr Marrero said he saw an increase in patient cases in late summer and early autumn – when forestry owners spray herbicide.

It was fascinating but not exactly conclusive. Perhaps everybody in New Brunswick had high levels of glyphosate and heavy metals, said sceptics, so it didn’t automatically follow that this was what was making the Marrero patients so ill. The province’s forestry industry insists it uses glyphosate in line with New Brunswick safety regulations.

A year after officials took over investigating the Marrero patients, they released a report that the neurologist’s defenders said was all too convenient: it said patients shared no common condition and environmental factors had not caused their symptoms.

Then, in May last year, an independent group of neurologists published their own report in a medical journal, concentrating on 25 Marrero patients, 14 living and 11 dead. It found all had been

suffering from conditions such as Alzheimer’s, Parkinson’s, cancer and Functional Neurological Disorder – the latter a condition in which the brain’s ‘software’ malfunctions, disrupting signals between the brain and body.

The neurologists said Dr Marrero had misdiagnosed case after case, but also blamed the spread of misinformation – fuelled by gullible media reports and increasing public distrust of healthcare institutions during the pandemic.

Ultimately, there never was any mysterious disease, they said. Dr Marrero had employed his undoubted charisma and charm to convince patients they didn’t need a second opinion when it was essential.

Dr Marrero said he ‘profoundly disagreed’ with the report but didn’t respond to the Daily Mail’s request for comment this week.

Although the province’s new governing party, the Liberals, insisted it would continue with its own investigation, many clearly regard it as case closed.

Most of Dr Marrero’s patients continue to support him. Some call him a ‘hero’ for his diligent work, when officials seem not to care whether they live or die. Medical experts say this sort of dogged loyalty is common among patients and their loved ones who become desperate for answers.

Marrero loyalists told the Daily Mail that the report’s authors have missed the point. It doesn’t really matter what they’re suffering from: what matters is why so many people in two small parts of New Brunswick are getting so ill.

Sarah Nesbitt, who runs a support group for Marrero patients, and Mandy Maillet both say tests have revealed they have high levels of glyphosate and heavy metals in their bodies.

Nesbitt insisted her own experience suggests the problem is environmental – many of her symptoms have subsided since she moved home and ‘detoxified’.

Others have not been so fortunate. Outside her home, Maillet pointed to the electricity substation less than 100 yards away that, she says, is regularly sprayed with glyphosate. She and her husband cannot afford to move away.

Whether or not they’ve been misled by an irresponsible brain clinician, one can only feel sympathy for Marrero’s patients – trapped in the middle of what seems like an eternal one-upmanship battle between the experts.

They can only hope the upcoming report provides answers. But somehow, given the history of this bizarre case, that seems unlikely.