We know what you’re thinking… How can you smell a disease? Well, there’s no way we humans can, but dogs’ noses bear 300 million scent receptors, compared with our mere 5 or 6 million. That enables them to detect tiny concentrations of odour that people can’t . Sniffer dogs are already a familiar sight in airports, where they detect firearms, explosives, and drugs. Scientists have also trained dogs to detect some cancers and malaria, but the animals are not routinely used for this purpose . Researchers don’t know for sure what the dogs are smelling, but many suspect that these illnesses cause the human body to let off a distinct pattern of volatile organic compounds (VOCs) . These molecules readily evaporate to create a scent that dogs can pick up. Previous work with non-COVID viruses has suggested that viral infections might also cause the body to do this . Humans have taken advantage of canines’ superior sense of smell for decades, and now canines are being trained to detect the whiff of COVID-19 infections around the world.
Dog trainers are claiming extraordinary results — in some cases, they say that dogs can non-invasively detect the virus with almost perfect accuracy- up to 94.3% sensitivity and up to 92% specificity [1, 3]. The dogs were able to detect odour from individuals who were asymptomatic, as well as those with two different strains, and with both high and low viral loads . The researchers acknowledge the results were achieved in a trial setting with the dogs trained in a controlled environment, however, they believe they could be replicated in real-world settings to help control the pandemic . Dogs could screen hundreds of people an hour in busy places such as airports or sports stadiums, and are cheaper to run than conventional testing methods such as PCR tests .
It takes eight to 10 weeks to train a Covid-19 detection dog. They are rewarded with an edible treat or ball for correctly indicating a positive sample or correctly ignoring a negative one . Dogs have been trained using sweat samples, T-shirts, socks, and masks donated by members of the public and NHS staff, some of whom had tested positive for COVID-19 [1, 4].
Though results are promising, most of these findings have not yet been peer-reviewed or published, making it hard for the wider scientific community to evaluate the claims . Researchers working on more conventional viral tests say that initial results from dog groups are intriguing and show promise, but some question whether the process can be scaled up to a level that would allow the animals to make a meaningful impact. Nevertheless, it will be interesting to see what comes of this in the future as our systems to manage COVID-19 globally progress.
Watch this clip for a brief overview on the subject by Sky News: https://www.youtube.com/watch?v=AuJw_WIU-i8
 Biology, M., Limited, O., (Pasteur-Lille), I. and Institute, F., 2021. Can dogs smell COVID? Here’s what the science says. [online] Nature.com. Available at: <https://www.nature.com/articles/d41586-020-03149-9> [Accessed 9 September 2021].
 LSHTM. 2021. Using dogs to detect COVID-19 | LSHTM. [online] Available at: <https://www.lshtm.ac.uk/research/centres-projects-groups/using-dogs-to-detect-covid-19#about> [Accessed 9 September 2021].
 Medicine, L. and Medicine, L., 2021. Bio Detection dogs identify COVID-19 with up to 94% accuracy | LSHTM. [online] LSHTM. Available at: <https://www.lshtm.ac.uk/newsevents/news/2021/bio-detection-dogs-identify-covid-19-94-accuracy> [Accessed 10 September 2021].
 The Guardian. 2021. Faster than a PCR test: dogs detect Covid in under a second. [online] Available at: <https://www.theguardian.com/world/2021/may/24/faster-than-pcr-test-dogs-detect-covid-coronavirus-london-bmj> [Accessed 10 September 2021].