Dogs can be trained to smell Parkinson's disease, UK research finds

New research from the United Kingdom suggests that dogs really can be trained to smell Parkinson's disease.

In a double-blind trial, a Golden Retriever and a Labrador identified which skin swabs had come from people with Parkinson's. The scent of oily secretions appeared to contain hidden clues.

“The dogs in this study achieved high sensitivity and specificity and showed there is an olfactory signature distinct to patients with the disease,” says Nicola Rooney, an animal behavioural scientist at the University of Bristol.

“Sensitivity levels of 70 percent and 80 percent are well above chance, and I believe that dogs could help us to develop a quick, non-invasive, and cost-effective method to identify patients with Parkinson's disease.”

The woman who could smell Parkinson's disease

There is currently no definitive early test for Parkinson's, which helps explain scientists' interest in finding possible biomarkers of the disease on the skin.

The discovery that Parkinson's causes a distinctive change in body odour emerged roughly a decade ago, thanks to one woman. Joy Milne sensed that something was wrong 12 years before her husband was diagnosed with Parkinson's disease: she could smell it.

A Scottish nurse known as a 'super-smeller', Milne became well known among neuroscientists in 2016 because of her remarkable ability.

During a small pilot study, she identified every patient with Parkinson's disease correctly using only the smell of their shirts. The one identification initially thought to be wrong proved to be correct almost a year later.

That finding prompted an important question: if Milne could smell Parkinson's years before diagnosis, might a dog be able to do the same?

Dogs have an extraordinary sense of smell, much more powerful than that of humans. Earlier studies have shown that our pets can detect our stress, coronavirus infections and even cancers by smell. If Parkinson's has a distinctive odour, dogs might therefore be able to detect that too.

Training dogs to detect Parkinson's

Over the past decade, several preliminary trials have offered evidence in support of that idea. However, some provided only limited details about how the dogs were trained and tested.

The recent UK trial brought together Medical Detection Dogs and neuroscientists at the University of Manchester. One aim is to establish what the dogs are smelling and why.

In 2019, Manchester researchers helped identify the odour compounds that distinguish the smell of Parkinson's. Milne, the fortuitous “super-smeller”, later confirmed their findings.

A few years later, those compounds were used to develop a diagnostic 'swab test' for Parkinson's, which is currently being tested. In time, trained dogs might also help neuroscientists identify further biomarkers unique to the disease.

How the dogs performed in the trial

Not every dog is suited to the task, however. In the current trial, just 2 out of 10 dogs completed training, and neither achieved a perfect result.

One dog incorrectly marked a tenth of the odour swabs from healthy people as indicating Parkinson's. The other produced false alarms less than 2 percent of the time.

Taken together, though, the dogs identified people with Parkinson's by smell at a rate well above chance, providing proof of principle.

“We are extremely proud to say that once again, dogs can very accurately detect disease,” says Claire Guest, chief executive of Medical Detection Dogs.

“There is currently no early test for Parkinson's disease and symptoms may start up to 20 years before they become visible and persistent leading to a confirmed diagnosis.

“Timely diagnosis is key… ”

The research was published in the Journal of Parkinson's Disease.