Dogs excel at sniffing out human illness
Now researchers are trying to build a machine version of the perfect dog nose
Dogs are amazing at a lot of things. Their cuddling skills are unrivaled (sorry cats), some breeds catch balls better than most football players, and they make the best of friends. One of their other notable talents is their impressive sense of smell. Their snouts have been something humans have taken advantage of for centuries or longer, whether it be for finding food, avoiding danger or, in recent years, detecting medical conditions such as cancer.
For decades doctors have observed that dogs can detect certain diseases in humans by simply sniffing it out, but scientists still don't understand how dogs are able to spot cancer or diabetes using only their noses. However, advancements over the last couple of years have brought researchers closer to solving this puzzle, which could lead to revolutionary treatment options for patients with cancer or diabetes.
Dogs can smell almost 10,000–100,000 times better than the average person. There are a variety of factors that make this difference so dramatic, from simple anatomical differences all the way to the gene expression of olfactory, or smell, receptor genes between humans and their furry pals.
Similar to wolves, the dog snout, with its generally long, narrow shape, was adapted for sniffing out food and intruders. This design allows for an increased surface area for methodically sniffing molecules within the air. Even the nostrils play a key role in this process, as pups will sniff with either their left or right side depending on the scent.
The dog brain is also specialized for maximizing on the nose’s potential. Olfaction is controlled in the brain through the limbic system, which also manages memories, behavior, and motivation. Unlike humans, where the size of limbic system is inversely related to the size of the isocortex, which controls higher-ordered function, these structures are similarly sized in dogs. Some scientists theorize that this is why dogs have a more refined sense of smell than we do. Dogs also have a more diverse and bigger catalogue of genes involved in smelling – they simply have a better sniffing toolkit.
A long-sniffing symbiosis
Humans quickly capitalized on our best friends’ eagerness to share their tools with us. People domesticated dogs tens of thousands of years ago. As early as the 1800s, and probably even earlier, dogs have been formally taking care of humans by assisting blind people and dramatically improving their quality of life. Not long after, the police began to take advantage of the ease of which dogs could be trained to help sniff out criminals; the earliest law enforcement dogs were assigned to the Jack the Ripper case in London in 1888.
Dogs are now routinely utilized as integral members of military and police squads throughout the world. If you’ve ever seen working service dogs, you’ve probably noticed they are mostly German Shepherds, Labrador Retrievers, and Mallinois. While there is some debate over whether these breeds actually smell better than others, such as the short-nosed pug, it appears these dogs are routinely used based on longstanding beliefs about how easy it is to train them. That’s not to say your adorable terrier wouldn’t be a great service/law enforcement animal, but it might be easier to get a lab to be well behaved in public.
Sniffing out disease
Within the last 15 years, diabetes alert dogs have become, for some type I diabetics, a revolutionary advancement. It all started as initial observations from patients that their pet dogs would begin to act differently, such as become more vocal, or nudge them, when their blood sugar dropped. Once scientists began to study this phenomenon, it turned out that this was more than just coincidence.
While the dogs could be sensing changes in their owner’s behavior, the overall consensus among researchers in the field is that the dogs are actually sniffing chemical changes in their owner’s breath or sweat – called volatile organic compounds (VOCs). A 2016 article was touted in the media as a study that revealed which VOC diabetes alert dogs detect, but upon further investigation, this study was limited, as it only showed that the compound in question, isoprene, increased in the exhaled breath of eight diabetic patients. While isoprene could be what dogs smell when their humans are having hypo-glycemic – low blood sugar – episodes, further research studies with much larger samples sizes are needed to actually understand if this is the case.
In addition to diabetes, the powerful dog nose has also been hyped by researchers, the media and organizations like Medical Detection Dog, as a diagnostic tool for a variety of cancers, including lung, breast, bladder, and prostate cancer. It all began almost 30 years ago when a Lancet study reported that a woman with malignant melanoma only ended up going to the doctor because her dog kept sniffing a skin lesion she thought was totally fine. Doctors commented that this case was particularly interesting since the woman’s cancer was at an early, curable stage. Cases like these prompted doctors to think that the dogs were some how sniffing out the cancer cells, perhaps by smelling shifts in VOCs.
Amazingly, many researchers have demonstrated that the metabolic changes that occur during tumor development actually result in either new VOC production or alter the concentration of VOCs normally present, which can serve as biomarkers for diagnosing many forms of cancer. Even more impressive is researchers have demonstrated that trained sniffer dogs can identify prostate cancer samples with 93 percent sensitivity just by sniffing urine samples from patients. However, similar to the diabetes alert dogs, researchers still do not understand which compound the dogs are detecting. But they are getting closer.
The same researchers that were able to train a German shepherd to identify prostate cancer samples recently revealed that they believe their trained snout is detecting the VOC sarocosine, which is a by-product of amino acid synthesis. Sarcosine was previously shown to be a biomarker of prostate cancer since its concentration in urine increases during early stages of the disease, making it an ideal diagnostic tool. Knowing this, the authors hypothesized that their trained dog would be able to identify artificial urine samples spiked with cancer-levels of sarcosine – and they were right.
While this study still doesn’t definitively reveal that dogs are actually smelling sarcosine in their owners or in urine samples, these results are still exciting for a couple of reasons. First, a known VOC associated with prostate cancer can be detected consistently using only a trained dog. Second, because this chemical is generally an early detection biomarker, this offers profound potential for getting patients diagnosed as soon as possible.
Should we have dogs in the clinic or in the lab analyzing samples? While dogs in lab coats would be adorable and would probably decrease patient stress, that’s probably not the best idea for a variety of different reasons. Medical detection dogs are incredibly expensive to train, costing upwards of $25,000, making them a hard commodity to have in every clinic or deserving household as well as isolating patients that cannot afford their own personal alert dog. Like people, dogs also get tired, bored and distracted after working hard, making variability an issue. However, if we could create an electronic version of the dog nose, diseases such as cancer or diabetes could be detected in a more consistent, quick and cost-effective manner.
This isn’t something that’s centuries away – a University of Rhode Island engineer, Otto Gregory, and his students recently created a “digital dog nose” to detect explosive devices – and it works! If we knew for sure what trained dogs detect in diabetics or cancer patients, there’s no reason why a medical version of this device couldn’t exist.
Imagine the increases in the quality of life in diabetics that no longer need to prick their finger constantly or for cancer patients that don’t have to be on chemotherapy for longer than necessary, all because of an adorable dog nose. The science needs to catch up, but we aren’t far behind.