Trained scent dogs exhibit a remarkable ability to detect COVID-19 infections with higher accuracy and efficiency compared to conventional RT-PCR tests, according to a review of studies. This innovative approach not only promises quicker results but also holds the potential to substantially reduce diagnostic costs, the researchers said.

A growing number of studies over the last two years has highlighted the power of dogs in detecting the stealthy virus and its variants, even when they are obscured by other viruses, like those from common colds and flu.

"It went from four papers to 29 peer-reviewed studies that include more than 400 scientists from over 30 countries and 31,000 samples," said Tommy Dickey, Distinguished Professor Emeritus at the University of California (UC) Santa Barbara, US.

Dickey and collaborator Heather Junqueira from BioScent, Inc. noted that the collective research demonstrates that trained scent dogs are "as effective and often more effective" than the antigen tests we're keeping handy at home, as well as the gold-standard reverse transcription polymerase chain reaction (RT-PCR) tests deployed in clinics and hospitals.

According to the study, published in the Journal of Osteopathic Medicine, not only can dogs detect the SARS-CoV-2 virus faster, they can do so in a non-intrusive manner, without the environmental impact that comes with single-use plastics.

Dogs have hundreds of millions of olfactory receptors, compared to roughly five to six million for humans, and a full third of their brains is devoted to interpreting smells, compared to a scant 5 per cent in human brains, the researchers said.

All these enhancements mean that dogs can detect very low concentrations of odours associated with COVID infections, they said.

"They can detect the equivalent of one drop of an odorous substance in 10.5 Olympic-sized swimming pools. For perspective, this is about three orders of magnitude better than with scientific instrumentation," Dickey said.

The researchers found that in some cases, dogs were able to detect COVID in pre-symptomatic and asymptomatic patients whose viral load was too low for conventional tests to work.

Dogs can also distinguish COVID and its variants in the presence of other potentially confounding respiratory viruses, such as those of the common cold or flu, they said.

"They're much more effective. Infact one of the authors that we quoted in the paper commented that the RT-PCR test is not the gold standard anymore. It's the dog," Dickey said."And they're so quick. They can give you the yes or no within seconds if they're directly smelling you," he added.

In some scenarios a dog gave the person a quick sniff, sitting down to indicate the presence of COVID. In others, the dog was given a sweat sample to smell, a process that could take a few minutes.

The speed is especially important in situations like the earlier phase of the pandemic when a gap of days between test and result could mean an exponential rise in infections if the person was positive, or scenarios that involve a high volume of people, the researchers said.

Scent dogs such as beagles, basset hounds and coonhounds would be ideal for the task, given their natural tendencies to rely on odours to relate to the world, but the studies showed a variety of other dogs are up to the challenge.

Given a few weeks of training, puppies and older dogs, males and females, purebreds, and mixed breeds all performed admirably, according to the study.

Despite these positive reviews, there remain challenges to placing dogs in the mainstream of medical diagnoses, although the animals have proven successful in the detection of other conditions, such as diabetes and cancer, the researchers said.

"There's quite a bit of research, but it's still considered by many as a kind of a curiosity," said Dickey.

Places that were open to using dogs in field experiments tended to be smaller countries such as Finland and Colombia, where there was a desire to explore fast and cost-effective methods of detecting COVID without having to wait for expensive tests to be developed or for reagents to become available, the researchers said.

"After conducting this comprehensive review, we believe that scent dogs deserve their place as a serious diagnostic methodology that could be particularly useful during future pandemics, potentially as part of rapid routine health screenings in public spaces,” Dickey and Junqueira added.

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