Almost instantaneously, dogs trained to sniff out signs of SARS-CoV-2 infection can indicate positive samples with greater than 90 percent accuracy, according to two preliminary studies published this month. Although such rapid results won’t replace the tried-and-true PCR test to confirm an infection, pups could offer “a suitable method for mass screening,” James Logan, an infectious disease researcher at the London School of Hygiene & Tropical Medicine who coauthored one of the studies, tells the BBC.
Logan and his colleagues trained Asher, Kyp, Lexi, Marlow, Millie, and Tala to alert their handlers when they caught the scent of a SARS-CoV-2 infection on clothing that came from an infected person. According to The Guardian, each dog communicates a positive sample differently: Millie sits and whines when she gets a scent, Tala wags his tail, while others stand perfectly still.
In the study, posted as a preprint, their sensitivity—or ability to accurately point out positive samples—ranged from 82–94 percent. The Guardian notes that PCR tests have about 97 percent sensitivity, and lateral flow tests—rapid tests that use antibodies to pick up on viral particles—have 58–77 percent sensitivity. The dogs’ specificity—how well they accurately identified negative samples—ranged from 76–92 percent.
Another study had 335 human participants, 109 of whom tested positive for SARS-CoV-2 from a PCR test, wipe their armpits with a cloth and put it in a jar. Nine dogs trained to indicate positive samples had 97 percent sensitivity and 91 percent specificity, according to France Bleu. The results were shared by the National Veterinary School of Alfort in France last week.
Logan’s team used electronic sensors to analyze the volatile organic compounds present in samples from infected and uninfected participants, confirming that the virus leads to a particular odor profile, presumably picked up by the dogs’ snouts.
According to the Associated Press, a number of countries have already deployed canines to detect SARS-CoV-2 infections. In Thailand, for instance, Labrador retrievers trained at Chulalongkorn University are screening samples with 95 percent accuracy—except when it gets close to dinner time. “5 p.m. is their dinner time. When it’s around 4:50, they will start to be distracted. So, you can’t really have them work anymore. And we can’t have them working after dinner either because they need a nap,” Kaywalee Chatdarong, the leaders of the research team, tells the AP. “They are living animals and we do have to take their needs and emotions into consideration.”