Sniffer dogs are a familiar sight at airports all over the world, where border agents use them to detect illegal substances and contraband.

Now some dogs are using their noses for a different purpose – coronavirus.

Dogs specially trained to detect Covid-19 will start sniffing passengers as part of a trial at Prague Airport.

Among the six selected dogs, there are both dogs that have been serving with the customs authority for several years and young ones.

“Our goal is to complete the training by the end of the year,” said to Czech newspaper Blesk.cz Petr Müller, in charge of cynology service at the customs administration.

The six dogs selected have already completed previous training and “it is now only necessary to teach them to mark another category of odor”, added Müller.

In June, a team in France using a small number of samples collected from human patients who had been tested for COVID-19 in PCR tests found a high degree of evidence that dogs could detect COVID-19 infections through differences in the smell of human subjects’ armpit sweat.

In Germany, researchers ran a small pilot study, published in July, with trained coronavirus-sniffing dogs—corona-schnüffelnder hunde—and showed that the dogs were able to distinguish between coronavirus-positive samples and a control group with an average sensitivity (the rate of detecting true positives) of 83% and a specificity (true negative rate) of 96% after only one week of training.

There are currently 71 dogs at the customs administration, focusing on seven areas: banknotes, alcohol, drugs, smuggled animals and plants, defense, weapons, and now COVID-19.