We have long relied on man’s best friend for their advanced sense of smell. Detection dogs are now common sights in airports and other public areas because they have the ability to quickly sniff out drugs, weapons and explosives. More recently, researchers have been using this same concept to detect diseases, including lung cancer. Recent studies suggest these superior smellers may also be able to play a role in slowing the spread of COVID-19.

How Dogs Sniff Stuff Out

For some time now, scientists have used dogs to sniff out a variety of illnesses, from Parkinson’s to cancer and, most commonly, diabetes. Though it is still a bit of a mystery, recent studies have started to give us insight into just how dogs are able to detect even the slightest scent. And for a disease with a symptom that may take away a person’s ability to smell, it feels a bit like poetic justice that dogs may be able to identify the coronavirus by smell.

Dogs’ noses have around 300 million scent receptors, making them superior smellers to humans who only have about 5 or 6 million. This amount of scent receptors allows dogs to create a mental view of the world around them. While their eyesight is poor in comparison to human eyesight, their noses more than make up for this. According to Senior Research Fellow and head of the Dog Cognition Lab at Barnard College Alexandra Horowitz, a dog can even detect a teaspoon of sugar diluted in a million gallons of water (the equivalent of two Olympic sized pools).

When it comes to detecting illnesses, researchers believe that sickness causes the human body to release specific volatile organic compounds (VOCs), which are emitted as gases and create a scent that, while undetectable to us, dogs can sense. Using this acute sense of smell, researchers are then able to work with dog trainers to condition the dogs to identify the distinct smell of certain diseases. Sweat, saliva or other bodily fluids are commonly used as samples to train the dogs. If the canine correctly indicates a sample that was positive for the disease being researched, they receive a treat or a toy. Indicating can look like sitting next to the sample, freezing with their nose pressed against it or even pawing at the sample. In previous studies for cancer and other illness, dogs have been nearly 100% successful when indicating a positive sample.

The COVID-19 Study

With the influx of COVID-19 cases, it makes sense that researchers would want to find a way to apply this science to detecting positive samples of the virus. One of the first studies took sweat samples from 177 possible COVID-19 patients in five different hospitals in Paris and Beirut. They then used these sweat samples to train 14 dogs, six of which were further tested in the study.

These five Belgian Malinois and one Jack Russell terrier that were chosen were then asked to detect a positive SARS-CoV-2 sample from a lineup of three or four cones that contained negative samples. The dogs did dozens of trials, with a success rate of between 76% to 100%. Two dogs that had previously specialized in detecting colon cancer, had a 100% success rate of the 68 tests they completed.

The dogs may even be able to detect false negative tests. During the testing, two samples collected from individuals who tested negative were repeatedly marked by the dogs. The relevant hospitals were informed, and in subsequent tests these individuals tested positive.

In addition, a surgeon and researcher at Saint Joseph University in Beirut, Riad Sarkis, further tested the best two performers by taking them to a Lebanese airport. The dogs screened 1,680 passengers and found 158 positive SARS-CoV-2 cases that were then confirmed by other viral tests. Amazingly, Sarkis found that his dogs could correctly identified negative results 100% of the time, and correctly detected positive cases 92% of the time, according to unpublished results.

How This Can Help Us

The hope is that this super sense can allow canines to contribute to the tools we have to slow the spread of SARS-CoV-2 because they can provide additional screening for hundreds of people in a short amount of time in busy places such as airports or sports stadiums. This may be especially helpful for those asymptomatic COVID cases in which a person is infected with SARS-CoV-2 but doesn’t realize it because they don’t have any of the symptoms. In fact, the Miami Heat had already begun to use dogs to screen fans before games. This can help reduce the spread of the virus by being able to identify potential virus carriers prior to them risking exposure to others in crowded areas. However, this is only one strategy utilized to protect against the spread of infection. The Heat’s stadium still requires masks be worn at all times and enforces social distancing as well as rapid testing for those that sit court side.

Using coronavirus sniffing dogs is much cheaper than conventional testing methods. "Even if trained dogs are able to correctly discriminate symptomatic COVID-19 positive individuals from asymptomatic negative ones, they should not be considered a perfect diagnostic test—but rather a complementary tool," the study said.

Even so, using dogs to help detect coronavirus may be part of our future, especially as we look forward to reopening public spaces and one day returning to life as normal.

For more information on COVID-19, visit Lung.org/covid-19.

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