New research shows that trained sniffer dogs can detect airport passengers infected with SARS-CoV-2, the virus responsible for COVID, with a degree of accuracy comparable to that of a standard PCR test.
The study, published in the open access journal BMJ Global Health, found that the sniffer dogs had about a 92% success rate in detecting samples with the infection and were even able to detect positive samples from people who had no symptoms.
Lead researcher Dr Anu Kantele, from the University of Helsinki, said that dogs have a very keen sense of smell and can pick up a scent at levels as low as one part per trillion, far exceeding any available mechanical techniques.
“It is thought that they can detect distinct volatile organic compounds released during various metabolic processes in the body, including those generated by bacterial, viral, and parasitic infections,” Dr Kantele explained.
“This method of detection is likely to be especially valuable, not only in the early stages of a pandemic when other resources might not yet be available, but also to help contain an ongoing pandemic.
“Dogs could be used both in sites of high SARS-CoV-2 prevalence, such as hospitals (to pre-screen patients and personnel), as well as in low prevalence sites, such as airports or ports to pre-screen passengers.
“This could save both considerable time and resources… Our preliminary observations suggest that dogs primed with one virus type can in a few hours be retrained to detect its variants.”
Four dogs (three Labradors and one White Shepherd) previously trained to sniff out illicit drugs or dangerous goods or cancer, were retrained in 2020 to sniff out the D614G Wuhan-like strain of SARS-CoV-2.
To test their detection skills, 420 volunteers provided four skin swab samples each, which were randomly presented to each dog over seven trial sessions.
Each dog sniffed skin samples from 114 of the volunteers who had tested positive for SARS-CoV-2 on a PCR swab test, and samples from 306 who had tested negative.
Overall, the diagnostic accuracy for all samples sniffed was 92%, with only minor variation between the dogs: the best performance reached 93% for sensitivity and 95% for specificity, while the worst reached 88% for sensitivity and 90% for specificity.
Amazingly, of the 28 positive samples that came from people who had had no symptoms, only one was incorrectly identified as negative, demonstrating that the lack of symptoms did not seem to affect the dogs’ performance.
To test their accuracy in real-life situations, the four dogs were then put to work sniffing out samples taken from 303 incoming passengers at Helsinki-Vantaa International Airport, Finland, between September 2020 and April 2021.
Each passenger took a PCR test to validate the results of the sniff-test and the study found that the dogs correctly identified 296 out of 300 (98%) samples.
For the seven incorrectly diagnosed samples, after re-evaluation with clinical and serological data, one was judged to be SARS-CoV-2 negative, one SARS-CoV-2 positive, and one a likely post-infectious positive PCR test result.
Similarly, the remaining four PCR negative cases indicated as positive by the dogs were all judged to be SARS-CoV-2 negative.