Science Sunday

Could Dogs be Used to Detect COVID19

Dogs have long been used to locate such things as drugs or explosives, and more recently to detect some diseases in humans. It is has been known since the time of Hippocrates, that exhaled breath odours could diagnose disease. For example, it was believed that the exhaled breath of a diabetes person presented a sweet odour, while for people affected by kidney failure it showed a fish like smell.

Cliff, C. difficile detection beagle

 ​The source of these various scents in now known to be Volatile Organic Compounds or VOC's.  These VOC's are exchanged from the blood to exhaled air in the alveolar portion of the lungs. The exhaled air will have a proportion of the VOC's in relation to the concentration in the blood. This is the method used for blood alcohol testing in law enforcement. Building a machine that can detect a particular VOC at concentration as small as one part in a trillion is a challenging enterprise to say the least. However, such a task is unnecessary since we already have an ideal detector that's willing to work for as little as a pat on the head.
One such detector was a beagle named Cliff.  When super-bugs became an issue, hospitals were especially susceptible to  Clostridium difficile (known as C. difficile). Cliff was trained to identify C. difficile from stool samples as a proof of concept, then was retired. Two years later Cliff was brought out of retirement when an outbreak occurred in a large hospital. Without any refresher retraining, he was put to work again. In the end, the little Beagle screened 371 patients. The dog correctly identified 12 out of 14 patients with C. difficile infections (a sensitivity of 86 percent) and 346 out of 357 infection free patients (a specificity of 97 percent). ​
 Recent studies reported in the journal Frontiers in Veterinary Science  found that the VOC's from different species of rhinovirus (common cold) were different enough to allow for detection and discrimination between them by specially trained dogs. So now, several institutions are racing to isolate the VOC's unique to COVID19 and to train dogs to identify them. One such study is ongoing at  London School of Hygiene and Tropical Medicine (LHTSM) .
“It’s very early stages,” says James Logan, head of LSHTM’s Department of Disease Control. “We know diseases have odours —  including respiratory diseases such as influenza — and that those odours are in fact quite distinct. There is a very, very good chance that Covid-19 has a specific odour, and if it does I am really confident that the dogs would be able to learn that smell and detect it.”
The actual source of the detectable scents created by diseases and viruses has not been determined, but Logan’s team believe they may be connected to the oxidative stress caused by infections.

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​“Oxidative stress can release compounds into the blood, which can be released through your breath and skin,” Logan says. “We think it may be something to do with the stress response to an infection that causes these different volatile chemicals to be produced, which are released into the blood and become detectable by the dogs. But we don’t know what the mechanism is.”

Training to identify COVID19

 Although we may not know the mechanism, we have successfully been able to train dogs in the past to identify several human maladies. Given previous successes with detection dogs the outlook seems promising. This will give authorities a real time detection protocol which can be rolled out quickly and greatly increase the ability to  do the tests in the numbers required for  safely re-opening at a very low cost and in real time.