Dogs are known to have a strong sense of smell and scent. This is not far-fetched because their nose contains up to 300 million olfactory receptors. Several studies over the years have shown that dogs can distinguish between healthy individuals and sick people living with conditions such as Parkinson’s disease, cancer, Methicillin-resistant Staphylococcus aureus (MRSA), etc.
Various countries are now looking into the potential of using dogs to detect people who are infected with the deadly Covid-19. Some early clinical trials already suggested they can.
Although dogs may not be as accurate as PCR tests for COVID-19, they have a good advantage in detecting smells, and that’s their speed.
Scent of disease
When it comes to detecting illnesses, researchers believe that the human body releases specific volatile organic compounds (VOCs), emitted as gas, and create a scent, which might be undetectable by human smell, but very ease to sense by dogs.
Scientists have established in cases of cancer that the changes in cellular proteins during cancerous cell growth usually release gaseous compounds that can be detected in people’s urine or on their breath.
However, in cases of coronavirus, it is still not clear whether dogs detect the bodily changes after infection or they detect the scent of the pathogens themselves.
How can dogs be trained to detect COVID-19?
It takes around 10 weeks to train a dog to detect COVID-19. The dogs are first trained to detect a scent that is non-biological and to indicate when they find it, using their unique “tell sign” e.g. wagging their tail or sitting down. Most times, they are rewarded with a toy or treat for correctly identifying a positive sample and ignoring the negative one.
After the dog has mastered these basic principles, the dogs are trained using face coverings or clothes of people who have been confirmed to have COVID-19.
Some good dog breeds often used for medical detection include:
- Golden Retrievers
- Labradors
- Spaniels
These dogs are not only good at searching out scents, but they are also temperamentally well-suited to support humans in public places.
Common case studies
Recent studies have shown that with cloth or sweat samples, dogs can distinguish between infected and non-infected individuals with a high level of accuracy.
One study conducted by researchers at Durham University in the UK and the London School of Hygiene and Tropical Medicine showed that dogs could rapidly detect COVID-19 with 94.3% sensitivity. This means that dogs could correctly identify 94 out of every 100 COVID-19 patients. This is a good result when compared with the PCR tests having a sensitivity of 97.2%, and rapid lateral flow tests with 58-77% sensitivity.
The research also showed that the dogs were 92% correct in identifying negative samples. The odor samples were collected from 1,097 infected patients and 2,031 uninfected people. But in general, the study involved 3,921 adults.
The second study conducted by researchers led by Dominique Grandjean at National Veterinary School in France showed that trained dogs were able to detect coronavirus with 97% accuracy. These dogs were also 91% correct in identifying negative samples.
This study involved 335 people and nine dogs. Out of the 335 people, 109 were found to be COVID-19 positive and confirmed through a subsequent PCR test.
However, these two pieces of researches haven’t been peer-reviewed. More so, further studies are needed to confirm that dogs can help achieve an accurate result when testing infected humans in real-world settings, including airports and other public spaces.
Another case studies collected sweat samples from 177 possible COVID-19 patients from five different hospitals in Beirut and Paris. These sweat samples were used to train 14 dogs and 6 of them were used in the study – 5 Belgian Malinois and 1 Jack Russell terrier.
The dogs were placed to detect a positive SARS-CoV-2 sample from the lineup of three or four cones with negative samples. The dogs made a success rate of 76% to 100%. Dogs that had been used previously to detect colon cancer had a 100% success rate out of 68 tests they completed.
The dogs used in this study were able to detect false-negative results. Two samples that were collected from individuals who tested negative were marked by the dogs repeatedly. And when the relevant hospitals were informed, confirmatory tests were carried out and the individuals were seen to test positive.
Airport screening
Normally, PCR tests involve collecting samples (mainly swabs of materials collected from the throat and/or nose) and sending them to the laboratory for processing. This usually takes about 24 hours or more to get a result.
Dogs, on the other hand, have the advantage of speed as they can detect coronavirus infections in under a second. However, they are unlikely to ever fully replace PCR tests – as they are more accurate.
Many sniffer-dog scientists have turned their attention to COVID-19 from the pandemic period, and growing research is still on to explore the ability of dogs to detect coronavirus.
Training dogs to smell COVID-19 takes time, and there would never be enough handlers and dogs to screen entire populations.
Nevertheless, they can still be useful at public transport hubs, such as airports, where passengers disembarking can be quickly put to screening. This is especially important for passengers arriving from high-risk countries. Dogs can be used to screen these people much as trained drugs and explosives sniffer dogs do.
After screening, those identified may still require to go through a confirmatory PCR test. And the passengers will be in quarantine while the PCR test is being conducted. However, this would significantly reduce the numbers having to do so.
Trials at airports in Finland, United Arab Emirates, and Lebanon are already using dogs to detect coronavirus in sweat samples for passengers. Dogs in Lebanon and Finland have even identified cases before conventional tests showed any result. This means that the dogs can spot the infection even before the symptoms begin to show up.
Apart from airports, dogs can also be stationed at the entrances of large public events, and anyone who is identified as COVID-19 positive would be refused entry.
Benefits of screening with dogs
The strong sense of smell of dogs is a great tool that we can maximize to slow the spread of COVID-19. Dogs can be used to screen hundreds of people in a short time. This is especially helpful for those asymptomatic cases of COVID-19 in which a person is infected but doesn’t realize it because there are no clear symptoms.
Miami Heat has already started using dogs to screen spectators before games. This helps a great deal to reduce the spread of the virus by identifying potential virus carriers before they risk exposure to other people in crowded areas. This is one strategy, however, to protect against the spread of the infection.
Despite the screening at the entrance, the Heat’s stadium still requires that you wear your mask at all times and enforces that you keep your social distance.
Another benefit of screening with a dog is that it is much cheaper than using conventional testing methods. However, using trained dogs should not be considered a perfect diagnostic test, but instead a complementary tool.
Conclusion
Dogs can be trained to smell COVID-19 as they have a well-developed sense of smell. They have been widely used in different places, including airports, stadiums, and other public places. However, they are not as accurate as of the PCR tests, so they are used as a complementary tool and not a complete replacement for laboratory diagnostics.
Using dogs, however, to detect diseases such as COVID-19 is already a part of our future, and they help a great deal to prevent the spread of deadly diseases.