Can animals detect human disease? - (2/26/2019)

By Dr. Ron Gasbarro

Freddy was in the pharmacy, complaining about politics, climate change, taxes, and his doctor. “The guy is clueless when it comes to diagnosing anything. I bet my dog could do a better job,” Freddy said to the pharmacist. “That’s not as far out as it sounds,” the pharmacist replied. 

A dog’s snout has 220 million cells that detect odors compared to a mere 5 million in humans. What does this mean? Professor Alexandra Horowitz is a dog-cognition researcher at Barnard College in New York. In her book, Inside of a Dog: What Dogs See, Smell, and Know, she writes that while we might know that our coffee has a teaspoonful of sugar added to it, a dog could detect a teaspoonful of sugar in a million gallons of water, about the size of two Olympic-sized swimming pools. And, although none have yet graduated from medical school, dogs can often outfox doctors in recognizing serious diseases.

Over the last few decades, researchers have assessed dogs' sniffing abilities when it comes to cancer. In these studies, dogs have been successfully trained to detect the disease comparing samples from known cancer patients to people without cancer. In a 2006 study, five dogs were trained to identify cancer based on human breath samples. Once trained, the dogs were able to detect breast cancer with 88% accuracy, and lung cancer with 99% accuracy. They could do this across all 4 stages of the diseases, including the very earliest stages of these illnesses. Other studies have shown that dogs can sense when an attack of narcolepsy is about to occur. This sleep-cycle disorder can occur when a person is driving – an extremely dangerous situation. The dog can alert the driver, potentially saving him from a car accident. A recent study showed that dogs can give a heads-up to a patient who suffers from migraines. In so doing, the patient can take her medication before the severe pain begins. A notable study took place in 2011, in which dogs in Japan detected colorectal cancer with 98% accuracy by sniffing breath samples. This is more accurate than the traditional diagnostic lab tests for the disease.

Dogs are not the only animals that have the ability to detect human disease. In a 2015 study at the University of Iowa, scientists discovered that pigeons can be trained to detect cancerous cells in a laboratory setting. On day one of testing, pigeons were accurate about 50% of the time. By day 15, they had improved to 85% accuracy. The birds were particularly good at identifying breast cancer cells.

Changes in body odor are known to be a consequence of many diseases. Much of the published work on disease-related body odor changes has involved parasites and certain cancers. Much less studied have been viral diseases, possibly due to an absence of good animal models. In 2006, China experienced an outbreak of bird flu, which sent the world into a panic over this obscure, yet deadly viral disease. Since then, American researchers have found that mice can be trained to identify birds infected with the illness, possibly before they have the chance to spread it to humans. A 2013 study taught mice to identify the feces of infected ducks. The mice were rewarded when they correctly identified feces from ducks with bird flu. Ultimately, the mice were accurate 90% of the time.

“That settles it,” said Freddy, “The next time my doctor thinks he has found something wrong with me, I’ll say ‘Thanks, Doc, but I’d like a second opinion. Let me ask my dog!’” 

Ron Gasbarro, PharmD, is a registered pharmacist, medical writer, and principal at Read more at 


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