by Grace Liu
Instead of temperature guns and mouth swabs, troops of Labradors and cocker spaniels could soon be roaming through airports, sniffing new arrivals for potential cases of coronavirus. Headlines suggest that one of the newest weapons in the fight against the COVID-19 pandemic may have four legs, an excitable tail and enjoy long walks. Since recruiting our canine companions to sniff out cases might sound just too cute to be true, we looked into the science behind these stories.
It’s not unusual to see a dog in the park, running around with their nose to the ground but I’m willing to bet that you’ve never seen a human do the same. With this in mind, it won’t come as a surprise to know that dogs have a much superior sense of smell. Compared to our human abilities, it has been estimated that a dog’s sense of smell is between 10,000 to 100,000 times more acute. The consequences of that enhanced ability are mind-boggling. Professor Alexandra Horowitz, dog-cognition researcher at Barnard College in New York writes that, while we might be able to detect one teaspoon of sugar added to a cup of coffee, a dog could detect the same amount of sugar, dissolved in two Olympic-sized swimming pools. Another dog scientist has likened their olfactory ability to being able to sniff out one rotten apple in two million barrels.
A nose for the deadly
Combined with their intelligence and capacity for training, dogs and their incredible smelling powers have already been deployed in a range of life-saving settings. Most people would be familiar with the sight of dogs at airports, sniffing baggage for explosives, drugs and other contraband items, or even heard about search-and-rescue dogs finding lost hikers by picking up their scent. More recently, dogs have also been trained to identify particular smells associated with a range of diseases. Bladder cancer from urine, lung cancer from breath, and ovarian cancer in blood samples are all now detectable by trained dogs. Specially trained dogs can also warn diabetics when their blood sugar levels are dropping dangerously low, or alert epileptic patients who are on the verge of a seizure.
Two years ago, a collaborative study between scientists and the British charity Medical Detection Dogs showed that dogs could identify socks worn overnight by children infected with the malaria parasite, sometimes even in cases so mild that the children showed no fever. According to Dr Claire Guest, director of Medical Detection Dogs, the dogs were probably not picking up a single chemical but rather a “tune of many notes” composed of a mixture of volatile compounds.
Volatile organic compounds are a huge class of chemicals that are released into the air at room temperature. This includes many compounds in our breath, sweat, saliva, tears and urine. Interestingly, this bouquet of aromas changes not only when we eat certain foods or do a heavy workout, but also in different health conditions. Within infected people, malaria parasites produce certain volatile compounds, like those found in perfume, that help attract mosquitoes to increase their transmission.
Smelly socks and saliva
Now scientists are asking whether coronavirus also triggers a change in body odour that can be detected by dogs. Around the world, several groups are already trying different tactics, varying mostly in how they are collecting the “coronavirus scent”, to explore this possibility.
A team from the London School of Tropical Hygiene and Medicine and Durham University, in collaboration with Medical Detection Dogs, recently received a £500,000 grant from the British government and is currently in the phase of sample collection. Health care workers, all of whom are COVID-19 symptom-free but some of whom may be infected, will wear a pair of sterilized nylon socks for a few hours. Nylon is “a very good matrix to collect odour”, says Professor James Logan, head of the Department of Disease Control at the London School of Tropical Hygiene and Medicine. Half of each sock will be sent to an analytical lab to determine the chemical composition of the odour, while the other half will be sent to the team at Medical Detection Dogs. At this training centre just outside of London, six specialist dogs that have previously shown the ability to detect diseases will undergo training on the COVID-19 samples.
Another study at the University of Pennsylvania’s School of Veterinary Medicine is at a similar pilot stage. Currently, eight Labrador retrievers are being introduced to saliva and urine samples from COVID-19 patients to see if they can discern a unique odour. “All the dogs are just now learning how to ignore odours that might be irrelevant,” Professor Cynthia Otto, director of Penn Vet’s Working Dog Center, told NPR. “The next step is going to be determining, is there a specific odour associated with COVID-19?”
More sensitive than a lab test?
Promising results have emerged from a French team at the National Veterinary School of Alfort just outside of Paris. In a preliminary study published in early June, the scientists strongly suggest that dogs could be trained to distinguish a COVID-19-specific odour exuded through underarm sweat. They reasoned that, not only is sweat unlikely to transmit the virus but that it also contains more volatile organic compounds and has a low chance of being contaminated by someone else. Eight dogs, with backgrounds ranging from detecting colon cancer to drugs and banknotes, were trained to sniff samples taken from COVID-19 patients over several hours. In the test phase, the dogs were presented with up to seven boxes in a row, only one of which contained a COVID-19 positive sample. Amazingly, four of the dogs showed 100% success in their trials. In a total of 176 trials, this super quartet identified the single correct sample every time and never incorrectly marked a negative sample. The other four dogs showed slightly lower but still impressive success rates ranging from 83 – 94%. Interestingly, the scientists noticed that there were two negative samples that the dogs constantly marked. When sent back to the lab for re-testing, it turned out that both were actually positive.
The progress from these three studies suggests that there might be a future for our canine companions as a quick and mobile detector for COVID-19. Researchers envision dogs working at airports, training stations and shopping centres – places where there is a heavy flow of commuters and limited opportunity for conventional testing. With dogs needing only half a second for a sniff, detection dogs at airports already screen up to 250 people per hour. Professor Logan from the UK study is optimistic, “If successful, this approach could revolutionise how we detect the virus.”