Dogs Sniff Out Covid-19 With Surprising Accuracy

Canines were even able to detect asymptomatic cases

An image of a detection dog sniffing a scent cone
Each pup was rewarded with toys like tennis balls if they picked out the virus successfully in sweat samples. GRANDJEAN D, et al. (2022)

Trained dogs have been used to find lost individuals, wildlife scat, invasive species, illicit goods and even cancers. A new study has shown that dogs may even be better at detecting Covid-19 than PCR tests.

The dogs' powerful snoots identified positive Covid-19 cases among 335 people at 97 percent accuracy after taking a whiff of human sweat samples, reports Aria Bendix for NBC News. And during the tests, the team found that the canines found all 31 Covid-19 cases in the 192 patients showing no symptoms. The study, led by Dominique Grandjean at the Alfort School of Veterinary Medicine in suburban Paris, was published in PLOS One. It suggests that with the proper scent work, canines could help obtain test results fast in mass screening efforts and reduce the need for invasive nasal swab tests.

Anecdotal evidence also suggested that dogs can pick up asymptomatic cases 48 hours before individuals test positive in PCR tests, reports Tina Hesman Saey for Science News. However, the dogs at times mistook another respiratory virus for SARS-CoV-2. The authors did not seem concerned with these cases—of the 17 false positives (cases where dogs mistakenly thought a sample was positive for SARS-CoV-2), only two were positive for another respiratory virus, though both cases were another kind of coronavirus.

For the study, the researchers used dogs from French fire departments and the Ministry of the Interior of the United Arab Emirates. Each pup was rewarded with toys like tennis balls if they picked out the virus successfully in sweat samples. The training took anywhere between three to six weeks, depending on the dog's experiences with odor detection, per Science News. The dogs used in the study had previous rigorous scent training, and many could sniff cancer, drugs or dangerous goods, per the Conversation's Hassan Vally.  

Each pup sniffed cones containing sweat samples from human participant's armpits, though swabbing sweat from the subjects’ neck and used face masks work well as samples, too, Grandjean tells Science News. If a dog sniffed a sample it thought was positive for Covid-19, it would sit down in front of it. It took about 15 seconds for the dogs to sift through 10 sweat samples from 10 different individuals that neither the dogs nor human handlers had interacted with before. Aside from detecting the virus, the dogs were also asked to find negative samples and identified the Covid-free samples with 91 percent accuracy, NBC News reports. 

Grandjean and his colleagues found that the dogs could detect infections earlier than PCR tests could, so they hypothesize that someone who may test negative on a PCR test but positive according to a dog may likely test positive on a PCR test two days later.

"Even with what we call a rapid test, you're still going to have to wait tens of minutes or even hours, where the dog in a matter of seconds or even fractions of seconds can make a response," Kenneth Furton, a chemist at Florida International University not involved with the study tells Science News.

While they could detect Covid cases, researchers still are unsure what the dogs are specifically smelling. Instead of one single chemical, it can be a mixture of decreasing or increasing aromas—receptors in the nose often do not detect one single molecule but are detecting complex mixtures. And just because dogs can smell Covid in sweat samples doesn’t mean the pets can do so on a full human body, which offers a greater combination of aromas.

"That's one of the big challenges — to have the dog learn to translate from a sample to an entire human being, which is a much more complex odor," Cynthia Otto, director of the Penn Vet Working Dog Center at the University of Pennsylvania, not involved with the study says to NBC News.

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