The Mechanism That Can Make Dogs Detect Viruses Up to 5 Days Before Symptoms – Coronavirus



Reproduction: BBC News Brasil

Coronavirus: the mechanism that can make dogs detect covid-19 up to 5 days before symptoms start

What does a person infected with Covid-19 smell like? This is an answer that only a dog could give us with precision.

The olfactory ability of one of our favorite pets has become yet another tool for fight the pandemic
Covid-19, which has already caused more than 20 million infections
and a million deaths worldwide.

In countries such as Finland, Lebanon, Argentina, Chile, Germany, the United States, Colombia and Mexico, authorities are training dogs to detect people infected with the new coronavirus.

A few weeks ago, dogs specially trained to detect Covid-19 by smell began to track passengers as part of a pilot program at Helsinki airport in Finland.

According to Professor Anna Hielm-Bjorkman, from the University of Helsinki, dogs can detect the virus in humans five days before symptoms appear.

Dog in training

MDD / Neil Pollock
Training is done with several samples of sweat smells

“They are very good [na detecção do coronavírus]. We are approaching 100% efficiency “, she explains.

Felipe Valencia, a Colombian veterinarian and specialist in dog training, develops a similar project in conjunction with the University of Antioquia, notes that the ability of dogs can make them very reliable in these cases.

“Dogs use 40% of the brain to process what they smell, so they can become an excellent tool to fight this disease,” he says.

The idea of ​​most of these programs is to use dogs in places where people arrive in countries, such as airports or train stations, in order to facilitate the movement of people without the need to impose restrictions or confinements.

A passenger prepares to be examined by a dog in Helsinki

Finland is already using dogs at airports

But how can dogs detect covid-19?

According to various surveys, it is difficult to establish what dogs actually smell.

Susan Hazel, a veterinarian at the University of Adelaide, Australia, explains in an article on the subject that dogs are trained with sweat samples from people, who may or may not be infected.

“The volatile organic compounds that are released from sweat samples are a complex mixture. Therefore, it is likely that dogs are detecting a particular mixture of smells, rather than individual compounds,” says the veterinarian.

Dogs, he adds, have an average of 220 million olfactory receptors in the nose, which allows them to detect minimal changes in substances.

The premise is the same as that of the team of experts from Chile, another country that trains dogs to detect Covid-19 in asymptomatic people.

Trainers with airport sniffer dogs

Sniffed dogs have helped fight the pandemic

“It is not that the virus has a particular odor, but the reaction that a person’s body has to the infection can be perceived,” veterinarian Fernando Madrones, from the Catholic University of Chile, told a local newspaper.

According to Madrones, when someone is infected with Covid-19, there are a series of metabolic reactions in the body, which in turn produces these volatile organic compounds, which are concentrated in the organs linked to sweat. This happens several days before the person has any symptoms. Urine, saliva and sweat samples have been used in experiments around the world.

Allies in combating various diseases

This is not the first time that dogs are used to detect disease. They have been used for some time to detect diseases such as diabetes, breast cancer and even Parkinson’s disease.

In the case of malaria detection, sniffer dogs are more effective than the tests of the World Health Organization “, says Professor John Logan, from the London School of Hygiene and Tropical Medicine.

Sniffer dog

Felipe Valencia
Felipe Valencia trained sniffer dogs for seven months


There are different methods of training dogs to detect the “smell” of a person with Covid-19, but most are based on the reward strategy.

“Although many of the dogs we work with already have a training base, they must first learn to recognize the virus,” Valencia tells BBC Mundo.

Valencia says that they receive samples, in this case of saliva from infected people, next to food or an object with which they usually train.

“Then the food or the object is removed and only the smell of the sick person remains,” says Valencia.

“The next process is to alternate these samples with others that do not contain the virus. When they recognize the one that contains the positive sample, they receive an award”, says the coach.

And when they accuse a sample that does not have Covid-19, they do not earn the reward and are motivated to go in search of the characteristic smell of contaminated people.

However, Valencia makes it clear that the effectiveness of the procedure depends a lot on the training that is done with the dogs.

“We have been in this process for more than six months. And I think that to reach a reliable level of effectiveness, we must work with dogs for at least four months”, he observes.

But can’t dogs be infected?

“No, there is really no possibility that they will become infected because the samples are protected by a material that prevents contact with the animal. In addition, we do regular tests to find out their health status”, says the trainer.

In the Finnish case, the dogs are already at the airport sniffing people entering the country. The rest of the countries are undergoing testing and training to ensure that the method is reliable.


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