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Dogs can be trained to detect up to 94 per cent of Covid-19 infections — even in asymptomatic patients — according to UK research published at the weekend, suggesting they could be used at airports and other entry points to screen passengers.

The study tested the known ability of dogs to act as biosensors, capable of detecting odours associated with human health — such as the presence of Plasmodium that causes malaria — as well as drugs, explosives and food.

Overall, the dogs were successfully able to identify between 82 and 94 per cent of samples of Sars-CoV-2, the virus that causes Covid-19. 

Researchers from the London School of Hygiene and Tropical Medicine wanted to know if dogs could detect a distinctive odour given off from chemical compounds associated with someone who is Covid-19 positive but doesn’t show symptoms.

They gathered samples of clothing and face masks from people. 

In one test, the socks of 200 Covid-19 cases were collected and arranged in lab tests for six dogs that had been trained to indicate either a presence or absence of the chemical compound. 

The team from LSHTM, Medical Detection Dogs and Durham University said the trial showed that Covid-19 infection “has a distinct smell which dogs can detect with incredible accuracy”. 

“To our knowledge, this study is the first to assess whether trained dogs can distinguish between the odour of people infected with Sars-CoV-2 and those who are uninfected, in a randomised double-blind trial, where trainer and monitor were unaware of the study group for each sample, and with a sufficiently high number of dogs and individuals donating samples,” the researchers wrote. 

The dogs needed to be trained not to identify “false positives” in a bid to obtain treats even if there were no Covid-19 samples in a given test.

The results are not yet peer-reviewed.

On Friday, Thailand deployed dogs trained to detect coronavirus infections by sniffing samples of human sweat, as the country deals with a surge in infections, including many asymptomatic cases.

Three of six trained Labrador retrievers had shown a success rate of about 95 per cent, similar to the UK study results.