Is there a doctor — or dog — in the house?

Molly Masland

The next time your dog decides to dive belly first into a pile of rotting fish or writhe in ecstasy in another dog’s feces, keep in mind that this seemingly horrifying urge could one day help save your life.

Dogs have long been used to sniff out explosives and drugs, track criminals and find missing children. Now, researchers are attempting to harness the olfactory powers of canines for use in the field of medicine.

Scientists are training dogs in the hopes that they may one day be able to reliably diagnose certain forms of cancer by smell, and help doctors catch these diseases earlier than conventional diagnostic tools currently allow.

Already dogs are used to warn of epileptic seizures, low blood sugar and heart attacks, although whether they are detecting changes in smell or physical behavior is still unknown. And, while they may not be able to perform CPR or operate a cardiac defibrillator (at least not yet), some canines do know how to call 911.

'This isn't anything magic'
Much of the research in this area is based on the theory that disease causes subtle chemical changes in the body or alterations in metabolism, which in turn releases a different smell, or chemical marker.

“This isn’t anything magic,” says Dr. Larry Myers, associate professor at the Auburn University College of Veterinary Medicine in Auburn, Ala., who has personally tested the olfactory capabilities of more than 4,000 dogs over the last two decades. “Physicians have always used their own senses to determine the presence or absence of disease.”

For instance, diabetes was once diagnosed by the smell or taste of a patient’s urine. Certain infections in burn victims can be detected by the smell of a patient’s skin, and bad breath is often a sign of gum disease.

Recent small-scale studies of dogs’ ability to detect the chemical markers of cancer, specifically melanoma, have shown promising results. The phenomenon was first briefly reported in 1989 in the British journal The Lancet and, since then, preliminary evidence has slowly been accumulating that suggests dogs may indeed be able to differentiate between healthy skin cells and cancerous ones.

A sophisticated sense of smell
Work is also under way to determine whether dogs can accurately diagnose prostate cancer. If the thought of a dog sniffing your private parts sounds just a little too, well, weird, have no fear: The dogs don’t actually smell men’s genitalia directly, they sniff urine samples instead.

Part of what makes a dog's sense of smell so sophisticated is its ability to smell multiple layers of chemicals, says Myers. Dogs don't detect a single chemical but a combination of them. "If (they were identifying) just a single chemical, medicine might have picked up on it. The dog may be doing something a little better," says Myers.

Surprisingly enough, no breed has a monopoly in the olfactory department; most studies have involved a number of different kinds of dogs. “There’s this mythology behind the bloodhound, but I’ve tested a miniature poodle that had a sense of smell that was as good as the bloodhound’s,” says Myers. “There’s enormous variability within the breed and on an individual level.”

The biggest challenge for scientists lies in designing experiments that can accurately determine dogs’ success rate in detecting disease and whether or not they perform better than existing diagnostic methods. Implementing rigorous controls has been a major obstacle, as has been finding adequate numbers of willing patients and doctors.

Correctly training the dogs themselves has also posed a difficulty for researchers. “You’re asking the dog to discriminate something by smell without knowing what the smell is,” says Dr. Jim Walker, director of the Sensory Research Institute at Florida State University, whose research on training dogs to detect melanoma will be published in Applied Animal Behaviour Science.

While it’s unlikely a canine will be joining the cast of ER anytime soon, researchers say if dogs do turn out to possess an ability to accurately detect disease, they could make a significant contribution to public health.

“It’s going to be very useful for large-scale screening of populations,” says Myers. “And it’s certainly going to be effective in third-world countries that don’t have the resources to do sophisticated (laboratory) tests.”

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