Dogs are really good at sniffing out coronavirus

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sniffer dogs COVID-19
Photo: Radila Radilova 123RF

Many long for a return to a post-pandemic ‘normal’, which, for some, may entail concerts, travel, and large gatherings. But how to keep safe amid these potential public health risks?

One possibility, according to a new US study, is dogs. A proof-of-concept investigation published in PLOS ONE suggests that specially trained detection dogs can sniff out COVID-19-positive samples with 96 per cent accuracy.

“This is not a simple thing we’re asking the dogs to do,” said Cynthia Otto, senior author on the work and director of the University of Pennsylvania School of Veterinary Medicine Working Dog Center. 

“Dogs have to be specific about detecting the odour of the infection, but they also have to generalise across the background odours of different people: men and women, adults and children, people of different ethnicities and geographies.”

In this initial study, researchers found the dogs could do that, but training must proceed with great care and, ideally, with many samples. 

The findings are feeding into another investigation that Otto and colleagues have dubbed “the T-shirt study”, in which dogs are being trained to discriminate between the odours of COVID-positive, -negative, and -vaccinated individuals based on the volatile organic compounds they leave on a T-shirt worn overnight.

“We are collecting many more samples in that study— hundreds or more—than we did in this first one, and are hopeful that will get the dogs closer to what they might encounter in a community setting,” Otto said.

Eight Labrador retrievers and a Belgian Malinois that had not done medical-detection work before were used in the study. First the researchers trained them to recognise a distinctive scent, a synthetic substance known as universal detection compound (UDC). They used a ‘scent wheel’ in which each of 12 ports is loaded with a different sample and rewarded the dog when it responded to the port containing UDC.

When the dogs consistently responded to the UDC scent, the team began training them to respond to urine samples from SARS-CoV-2 positive patients and discern positive from negative samples. 

The team found that after three weeks of training, all nine dogs were able to readily identify SARS-CoV-2 positive samples, with 96 per cent accuracy on average. Their sensitivity, or ability to avoid false negatives, however, was lower, in part, the researchers believe, because of the stringent criteria of the study—if the dogs walked by a port containing a postive sample even once without responding, that was labeled a “miss.”

The researchers ran into many complicating factors in their study, such as the tendency of the dogs to discriminate between the actual patients, rather than between their SARS-CoV-2 infection status. The dogs were also thrown off by a sample from a patient that tested negative for SARS-CoV-2 but who had recently recovered from COVID-19.

“The dogs kept responding to that sample, and we kept telling them no,” Otto said. “But obviously there was still something in the patient’s sample that the dogs were keying in on.”

Major lessons learned from the study, besides confirming that there is a SARS-CoV-2 odour that dogs can detect, were that future training should entail large numbers of diverse samples and that dogs should not be trained repeatedly on the samples from any single individual.

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