| Published: Friday, May 26, 2023, 11:16 [IST]
While we humans generally experience the world through sight, dogs use scent to learn about the environment around them. What their nose knows is crucial for finding food, mates and safe spaces. Our furry friends can also use their sniffing power to learn how people are feeling.
For example, they can detect the scent of fear in human sweat. Given this, it's perhaps not surprising that pooches' super-smelling skills can extend to monitoring human health - including, potentially, by detecting infectious diseases such as COVID. In a recent study undertaken in Californian schools, dogs were found to detect the virus with 95% sensitivity in a controlled laboratory setting and 83% in schools.
The olfactory capability of dogs far exceeds our own. Estimates suggest that dogs' smelling ability might be up to 10,000 times better than ours, thanks to having more than 100 million scent receptors in their nose (compared to six million in people). Dogs can detect a wide range of different smells at much lower concentrations than humans or even hi-tech laboratory instruments - sometimes as low as at one part per trillion. Interestingly, dogs use their nostrils separately.
They start sniffing with their right nostril, and if the smell is familiar and "safe", they switch to using their left nostril. Dogs differ in the shape and size of their noses, of course, but all have an impressive ability to detect scent in a range of situations. And not only are dogs good at sniffing, they love to do it. Allowing dogs to sniff can actually improve their welfare and make them more optimistic.
Dogs have shown they can accurately identify a variety of infectious diseases via scent. For example, children infected with malaria parasites were successfully identified by dogs sniffing their foot odour. Dogs can also detect bacterial urinary tract infections, and gastrointestinal infections caused by the bacteria Clostridium difficle, which can be life-threatening in vulnerable patients. Early in the COVID pandemic, it became clear that there was a need for extensive, real-time, accurate detection of infection. Respiratory infections cause the release of a range of substances that each have their own distinct smell.
Given dogs' success in detecting other infectious diseases, the potential role of dogs as "lab partners" during the pandemic was quickly explored. Initial research revealed that after just one week of training on COVID-specific odour, dogs were able to identify infections in bodily fluids from the respiratory system, correctly identifying positive cases 83% of the time. Once trained on respiratory samples, dogs were also capable of generalising their COVID detection skills to other bodily fluids, such as sweat and urine. The potential for real-time screening with a high degree of sensitivity offers several advantages over traditional COVID testing methods, such as lateral flow and PCR testing, including cost and efficiency.
Screening by sniffing
In the recent study, two dogs already trained to detect the scent of COVID in the lab were taken into 27 Californian schools and completed 3,897 screenings, mostly among students, by sniffing their ankles and feet. For comparison and to check accuracy of detection, participants also undertook lateral flow tests. After initial training, the dogs were detecting the virus in the lab with 95% sensitivity (correctly identifying positive cases) and 95% specificity (correctly identifying those who did not have COVID).
Screening people directly saw a slight drop in sensitivity to 83% and specificity to 90%. This is slightly lower than some estimates of the sensitivity and specificity of lateral flow tests, though their reported effectiveness has varied in different stud...
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