Dogs have been trained to sniff out cases of COVID-19. This canine in the United Arab Emirates takes a whiff of a sample through a special cone. These dogs are as reliable as lab tests, a new study suggests.
Nosaïs Team (CC BY 4.0)
Two years ago, several groups of scientists showed dogs could reliably identify the scent of people who had COVID-19. Now one of those groups has gone on to show that dogs are every bit as reliable as lab tests at detecting cases of COVID-19. And they’re even better than PCR tests for identifying infected people who don’t have symptoms. A big bonus: The canines are less invasive than a swab up the nose. And much cuter.
The new study trained dogs to smell sweat samples from 335 people. These canines sniffed out 97 percent of the cases that were found to be COVID-positive in PCR tests. And they found all 31 COVID-19 cases among 192 of the infected people who had no symptoms. Researchers shared their findings June 1 in PLOS One.
PCR tests can sometimes go wrong. But “the dog doesn’t lie,” says Dominique Grandjean. He’s a veterinarian at the National School of Veterinary Medicine of Alfort in Maisons-Alfort, France. He also led the new study and a smaller, pilot study back in 2020.
In the latest study, the dogs sometimes mistook another respiratory virus for the coronavirus, Grandjean and his colleagues found. But overall, the canine noses picked up more COVID-19 cases than did antigen tests, like most at-home tests. And some evidence, he says, suggests the dogs can pick up symptom-free infections up to 48 hours before people test positive by PCR.
Dogs could help screen crowds at places such as airports, schools or concerts, says Grandjean. And the animals may provide friendly alternatives for testing people who balk at nasal swabs.
The study included dogs from French fire stations and from the Ministry of the Interior of the United Arab Emirates on the Persian Gulf. The researchers trained the animals to detect coronavirus by rewarding them with toys — usually tennis balls. “It’s playtime for them,” Grandjean says. It takes about three to six weeks to train a dog to pick out COVID-19 cases from sweat samples. How long it takes depends on the dog’s experience at detecting scents.
The dogs then sniffed cones housing samples of sweat that had been collected from the underarms of volunteers. Sweat swabbed off the back of people’s necks worked, too. Even a whiff of used face masks worked well, Grandjean says.
These results show that odors from any of multiple sites on the body can be used for canine screening, says Kenneth Furton. He is a forensic chemist at Florida International University in Miami.
Although Furton did not take part in the new study, he has tested dogs at detecting COVID-19. The new results are similar to previous, smaller studies, he notes. Both show that dogs perform as well as or even better than PCR tests for detecting SARS-CoV-2. That’s the virus that causes COVID-19. He and his team have used dogs at schools and a music festival. They even did a small trial to screen airline employees for COVID-19.
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One big advantage of dogs over other tests is their speed, Furton says. “Even with what we call a rapid test, you’re still going to have to wait tens of minutes or even hours,” he notes. The dog can make a judgment call “in a matter of seconds or even fractions of seconds,” he notes.
It’s not clear exactly what dogs are smelling when they detect COVID-19 or other diseases, says Cynthia Otto. A veterinarian, she works at the University of Pennsylvania School of Veterinary Medicine in Philadelphia. There she directs the school’s working dog center. What the dogs pick up on may not be a single chemical, she says. Instead, it could be a pattern of changes. For example, they may detect more of certain aromas and less of others. “It’s not like you could create an odor perfume bottle that would be the scent of COVID,” she suspects.
To date, some doctors, scientists and government officials have been skeptical of the claims that dogs can sniff out COVID, Grandjean says. He finds this reluctance puzzling. Governments already use dogs to sniff out drugs and explosives. Some are being tested for detecting other diseases, such as cancer, he says. “Every time you take a plane, it’s because dogs have been sniffing your luggage [and found] no explosives. So you trust them when you take a plane,” he says, “but you don’t want to trust them for COVID?”
People may not think of dogs as high-tech the way electronic sensors are. “But dogs are one of the highest-tech devices we have,” Furton says. “They’re just biological sensors, instead of electronic sensors.”
One of the bigger drawbacks for dogs is that they take time to train. Right now, there aren’t even enough dogs trained to detect explosives, let alone diseases, Otto says. Not just any dog will do. “Dogs that work well in that lab setting may not work well in a people setting,” she adds. Handlers can also influence the dog’s response and must be able to read the dog well, she says. “We need more good dogs.”
cancer: Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.
canine: Members of the biological family of canids. These are carnivores and omnivores. The family includes dogs, wolves, foxes, jackals and coyotes. (in anatomy) The pointed tooth in a mammal that separates its incisors from its premolars. These canine teeth tend to be especially long in carnivores.
chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
colleague: Someone who works with another; a co-worker or team member.
coronavirus: A family of viruses named for the crown-like spikes on their surface (corona means “crown” in Latin). Coronaviruses cause the common cold. The family also includes viruses that cause far more serious infections, including SARS and COVID-19.
COVID-19: A name given to the disease that erupted into a massive global pandemic in 2020. It first emerged in 2019 and is caused by a new coronavirus known as SARS-CoV-2. Symptoms can include pneumonia, trouble breathing, feeling too tired to walk more than a few steps, fever, headaches, low blood-oxygen levels, blood clots and brain “fog.”
forensic: And adjective referring to the use of science and technology to investigate and solve crimes.
infection: A disease that can spread from one organism to another. It’s usually caused by some type of microbe.
invasive: An adjective that refers to something that can alter some environment (such as invasive medical procedures) or invade some environment (such as an invasive species).
nasal: Having to do with the nose.
PCR: An acronym for polymerase chain reaction. It's a biochemical process that repeatedly copies a particular sequence of DNA.
respiratory: Of or referring to parts of the body involved in breathing (called the respiratory system). It includes the lungs, nose, sinuses, throat and other large airways.
SARS-CoV-2: A coronavirus that emerged in Wuhan, China, in late December 2019. It would go on to cause widespread — and sometimes lethal — disease throughout China and many other nations. Its name reflects its close similarity to the original coronavirus known as SARS (for severe acute respiratory syndrome). That SARS virus sparked a global outbreak of disease in 2003.
screening: A health test that is performed early, often before any symptoms are present. Such tests can help find disease when it is easiest to treat. Screenings can include blood tests (such as for HIV, diabetes or high cholesterol), X-rays or scans (such as mammograms for breast cancer).
sensor: A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly. (in biology) The structure that an organism uses to sense attributes of its environment, such as heat, winds, chemicals, moisture, trauma or an attack by predators.
skeptical: Not easily convinced; having doubts or reservations.
symptom: A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.
test positive: A term that indicates that some test has confirmed what it was looking for, such as a disease or poison.
United Arab Emirates: A nation made of seven states, called emirates, that lies along the southern coast of the Persian Gulf. This oil-rich country, sometimes called the Emirates, shares a border with Saudi Arabia and Oman. Getting only 100 to 150 millimeters (4 to 6 inches) of rain each year, it hosts a large rocky desert, coastal wetlands and arid mountains.
veterinarian: (adj. veterinary) A doctor who studies or treats animals (not humans).
virus: Tiny infectious particles consisting of genetic material (RNA or DNA) surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact many scientists argue that no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.
Journal: D. Grandjean et al. Diagnostic accuracy of non-invasive detection of SARS-CoV-2 infection by canine olfaction. PLOS One. Vol. 17, June 1, 2022, p. e0268382. doi: 10.1371/journal.pone.0268382.
Journal: D. Grandjean et al. Detection dogs as a help in the detection of COVID-19 Can the dog alert on COVID-19 positive persons by sniffing axillary sweat samples? Proof-of-concept study. June 5, 2020. bioRxiv preprint. doi: 10.1101/2020.06.03.132134.
Tina Hesman Saey is a senior staff writer and reports on molecular biology at Science News. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.
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