Covid-19: Dogs can smell the virus

The nose of dogs again has done its «miracle», as it seems from small tests so far that man's «best friends» have a remarkable ability to smell the infection from the new coronavirus and make their own... diagnosis. Scientists believe that large trials are now needed to confirm how accurately this is actually happening and whether this olfactory ability could be used in practice, as it is a cheaper method than tests.

Already, according to Nature, dogs are being trained to detect Covid-19 in different parts of the world. In some cases, dog trainers report, the friendly animals have near-perfect accuracy in detecting the virus. For this reason, some scientists believe that dogs are in a position to help control the pandemic, for example by «checking in» thousands of people at airport gates, stadiums, department stores and other crowded places.

So far, however, most of the findings so far on dogs and coronavirus have not been reported in scientific journals, making it difficult for the scientific community to evaluate the claims and distinguish truth from exaggeration. However, several researchers believe that the results so far show promise and should be studied further. A key question to be answered is to what extent dogs can make a practical contribution to the battle to contain the pandemic.

«No one is arguing that dogs can replace a PCR molecular testing machine, but they can help,» according to German veterinarian Holger Falk of the University of Hannover's School of Veterinary Medicine, who is leading the Covid-19 detector dog training effort.

The nose of dogs has 300 million cell receptors for smell, compared to only five to six million in humans. Thus, dogs can smell subtle odors that humans don't even notice. That's why, after all, dogs have been trained for decades to perform various tasks to assist police, military, firefighters, doctors, etc., sniffing out everything from drugs and explosives to cancer and malaria.

In the case of diseases, scientists believe - without always being sure - that dogs smell characteristic organic volatile chemicals (VOCs) emitted by the sick human body. Previous research with viruses (not the new coronavirus) has shown that viral infections can also cause distinct body odors, so subtle that humans rarely notice, but dogs can much more easily.

Already, almost from the beginning of the pandemic, some scientists began testing dogs' Covid-19 abilities by training animals in laboratories to sit down or hit the floor whenever they smell the SARS-CoV-2 coronavirus in samples, usually of human sweat. Similar tests have already been done at airports in the United Arab Emirates, Lebanon and Finland with dogs, which were asked to sniff sweat samples from passengers and the results were compared with those of molecular tests done by the same people. According to the researchers, there were several cases where the dogs detected passengers with coronavirus, even asymptomatic ones, before the test results were available.

In the case of the Lebanese airport, French and Lebanese researchers, led by Dr Riad Sarkis of Beirut's Saint Joseph University, put two dogs to sniff 1,680 passengers and found 158 infected with coronavirus, as confirmed by subsequent molecular tests. The animals correctly detected 100% of those without coronavirus and 92% of those with the virus. Already, according to Sarkis, he has been approached by schools, banks, prisons and department stores to use such coronavirus-trained dogs.

Especially poorer countries with little laboratory infrastructure could be helped by dogs in detecting cases, according to virologist Dr Isabella Eckerle of the Geneva University Hospital.

The only published small pilot study on the subject so far (by Falk's team in Germany), which involved eight dogs and only 14 humans - seven patients and seven healthy ones - showed that the animals were able to detect 83% in virus positive humans and 96% in negative ones.

A French research team, led by veterinarian Dominique Grandjean of the National Veterinary School near Paris and involving Lebanese Sarquis, which pre-published in bioRxiv this summer, used eight trained dogs to sniff out 198 sweat samples, about half of which were from Covid-19 patients. The animals detected virus positive samples at a rate of 83% to 100%, while no data were provided on the rate in the negative (coronavirus-free) samples. It does not appear, however, that all dogs do equally well: Two dogs found 68 out of 68 positive samples, while one lost ten out of 57.