Dogs are as reliable as laboratory tests in detecting cases of COVID-19 and may be even better than PCR tests in identifying infected people who do not have symptoms. One bonus: canines are cuter and less invasive than a swab up the nose.
In a study of sweat samples from 335 people, dogs trained detected 97 percent of coronavirus cases who had been identified by PCR tests, researchers report June 1 in plus one. And the dogs found the 31 cases of COVID-19 among 192 people who had no symptoms.
These findings are evidence that dogs could be effective for mass screening efforts in places like airports or concerts and may provide friendly alternatives for testing people who are resistant to nasal swabs, says Dominique Grandjean, a veterinarian at the National School of Veterinary Medicine of Alfort in Maisons-Alfort, France.
“The dog doesn’t lie,” but there are plenty of ways PCR tests can go wrong, says Grandjean. Canine noses also identified more cases of COVID-19 than antigen tests (Serial number: 12/17/21), similar to many home tests, but sometimes mistaking another respiratory virus for the coronavirus, Grandjean and colleagues found. In addition, anecdotal evidence suggests that dogs can detect asymptomatic cases up to 48 hours before people test positive for PCR, he says.
In the study, dogs from French fire stations and the United Arab Emirates Ministry of the Interior were trained to detect the coronavirus by rewarding them with toys, usually tennis balls. “It’s time to play for them,” says Grandjean. It takes three to six weeks, depending on the dog’s experience with scent detection, to train a dog to detect cases of COVID-19 from sweat samples.
The dogs then sniffed cones containing sweat samples collected from the armpits of human volunteers. Wiping sweat off the backs of people’s necks or giving woofers a whiff of used face masks worked just as well, says Grandjean.
Those results indicate that odors from multiple body parts can be used for canine detection, says Kenneth Furton, a forensic chemist at Florida International University in Miami, who was not involved in the study.
The results are similar to previous, smaller studies that also found that dogs perform as well or even better than PCR tests in detecting SARS-CoV-2, the virus that causes COVID-19, says Furton. He and his colleagues have used dogs in schools, a music festival and in a small trial to test airline employees for coronavirus infections.
One of the biggest advantages dogs have over other tests is their speed, says Furton. “Even with what we call a rapid test, you’ll still have to wait tens of minutes or even hours, where the dog within seconds or even fractions of seconds can respond.”
It’s not clear exactly what dogs smell when they detect COVID-19 or other illnesses, says Cynthia Otto, director of the working dog center at the University of Pennsylvania School of Veterinary Medicine, who was not involved in the study. It may not be a single chemical, but rather a pattern of increasing and decreasing levels of certain scents. “It’s not like you could create a scented perfume bottle that would be the smell of COVID,” she says.
Even with repeated studies showing dogs’ COVID-sniffing prowess, some doctors, scientists and government officials have been skeptical of the claims, says Grandjean. He finds the reluctance disconcerting, because the dogs are already used to sniffing out drugs and explosives, and are being tested for other diseases, such as cancer, he says. “Every time you take a plane, it’s because the dogs have been sniffing your luggage [and found] no explosives. So you trust them when you get on a plane, but don’t want to trust them for COVID?
One challenge with dogs, says Furton, is that people don’t think of them as high-tech as electronic sensors are. “But dogs are one of the most high-tech devices we have. They are just biological sensors, rather than electronic sensors,” he says.
Another drawback for the dogs is that they take time to train, and there aren’t even enough dogs currently trained to detect explosives, let alone disease, says Otto. And “dogs that do well in that lab setting may not do well in a people setting,” she says. Handlers can also influence the dog’s response and must be able to read the dog well, she says. “We need more good dogs.”