Tommy Dickey, PhD, provides a demonstration showing children how canine scent detection works. These dogs were not used in the research.
The nose knows

Scent detection dogs can identify individuals with COVID-19, research finds

The use of trained scent detection dogs to detect volatile organic compounds associated with the COVID virus shows promise in early studies.

In a recent article in the Journal of Osteopathic Medicine, authors reviewed previously published research to summarize current thinking on the feasibility and efficacy of using scent detection dogs to screen for the COVID-19 virus. The authors report that sensitivity, specificity, and overall success rates from four canine scent detection studies were comparable or better than the standard RT-PCR and antigen testing procedures.

These findings indicate that scent detection dogs could likely be used to effectively screen and identify individuals infected with the COVID-19 virus in hospitals, senior care facilities, schools, universities, airports, and even large public gatherings for sporting events and concerts.

“Accurate and rapid screening of individuals who may be carriers, symptomatic or asymptotic, of the COVID-19 virus will remain important for slowing and limiting the spread of infection,” said review author Tommy Dickey, PhD, professor at the University of California Santa Barbara. “These preliminary studies suggest the use of medical scent detection dogs offers a promising approach.”

Documented success detecting disease

Using inhaled air molecules and particulates, dogs can detect odorous human molecules (volatile organic compounds, or VOCs) that originate from flaked off skin or hair cells, blood, breath, saliva, sweat, tears, nasal mucous, urine, semen, or feces. These VOCs are produced by human tissues that have evolved into particular pathologic states associated with specific diseases. Since smells linger, dogs can maintain a historical library of the smells of complex molecules.

“The science behind and efficacy of using dogs in detecting medical conditions and diseases such as cancers, diabetes, malaria, Parkinson’s disease, and more has been documented,” said review author Heather Junqueira. “Our review of global studies provides support for additional research to determine their ability to detect COVID-19 at scale.”

Prior COVID-19 scent detection studies

For their review, the authors assessed four recent studies analyzing the success of scent-detecting dogs at identifying VOCs associated with COVID-19.

First, they described the work of a team of collaborating researchers from France and Lebanon, who tested with eight dogs that had previously been trained to detect both explosives and colon cancer. These dogs were independently presented with cotton or wool gauze samples that had been soaked with sweat from one of 198 human armpits of patients in different hospitals.

While the COVID-19 virus does not itself have a smell, researchers hypothesized that the resulting infection generates metabolic changes, which cause the release of a distinctive type of sweat odor that can be detected by a dog. 

The dogs were trained to only sit in front of a COVID-19-positive sample contained in a box with a sample canister. A “trial” consisted of one dog detecting the presence of the COVID-19 positive sample in one box out of three, four, six or seven boxes positioned in a line. After four days of training using COVID-19 samples, the success rate for the dogs ranged between 83 and 100%.

In another study the authors described, a research team in Germany conducted a randomized, double-blinded, controlled pilot study to determine whether previously trained scent dogs could successfully detect the presence of the COVID-19 virus. Again, eight dogs were trained for one week to detect the COVID-19 virus in samples of saliva or tracheobronchial secretions collected from infected patients.

Each dog, its handler, and the person observing the study were blindfolded. The number and duration of each dogs’ “nose dips” into the scent holes, along with the location of the positive and negative samples, were automatically recorded and verified using time-stamped video analysis, which automated the process and reduced trainer interference.

The results, derived from 1,012 automated sample presentations, showed an overall average detection rate of 94%: 157 correct indications of positive, 792 correct rejections of negative, 33 false positives, and 30 false negative indications. Interestingly, the team reported no notable difference in detection ability between the use of sample saliva and sample tracheal secretion.

While that pilot study had limitations—in particular, the positive samples came only from severely affected, hospitalized COVID-19 patients, and the negative samples were from healthy individuals with no indications of respiratory infections—the authors of the study found those results encouraging.

Support for additional research

A third study done by a team in Colombia tested six trained scent dogs of various and mixed breeds to develop a screening method for detecting COVID-19 in individuals who may be asymptomatic, pre-symptomatic, or symptomatic. Their work was motivated in part by concern for countries with economies particularly susceptible to poverty, malnutrition, and potential social unrest.

The researchers developed a device to safely expose the scent-trained dogs to VOC samples collected from respiratory secretions of COVID-19-positive patients, and their detailed study is being conducted in three phases, with the third phase ongoing.

“Of the 6,000 samples, the dogs’ performances [in that study] resulted in a sensitivity of 95.5% and a selectivity of 99.6%,” said Dickey. “The high success rates among different types of dogs suggests a range of breeds or mixed breeds may be trained to effectively screen for COVID-19.”

Challenges remain

While these research results are encouraging, there are still challenges to be considered before implementing canine COVID screening on a broad scale, Junqueria says. These include limited information on whether medical detection dogs can contract and become ill with COVID as well as the need for larger studies.

“Nonetheless, the research soundly supports the use of scent-detection dogs for pilot COVID-19 screening studies in venues such as airports and sporting events,” she notes.

The authors hope that their research review will be used to assist in the development of future studies and the implementation of screening programs to benefit preventative medical research.

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