Psychological health

Can Dogs Sniff Out Disease?

dog nose;

Source: Mark Watson, via Wikimedia Commons. Distributed under the CC BY 2.0 license.

Humans have always known that dogs’ noses are something special. We regularly train dogs to use their sense of smell – which is estimated to be about 10,000 to 100,000 times as much as our sense of smell – to sniff out bombs, drugs, firearms, and people. But what about detecting the smell of disease?

The first report of a dog alerting its owner to the disease, published in 1989, described a dog that was constantly sniffing and hitting a mole in its owner’s leg, which turned out to be a melanoma. This sparked the idea that cancer and other diseases could be detected by smell, and that dogs could be used as diagnostic tools.

Since then, numerous studies have examined dogs’ ability to smell diseases, including cancers, bacterial infections, seizures, COVID-19, and diseases affecting other animals and plants.

in New review paperan animal welfare scientist at Texas A&M University Courtney Diggle He and his colleagues evaluated existing studies of canine olfaction to determine the extent to which dogs can act as reliable indicators of disease.

“This happened because one of our collaborators asked me if I thought we could use dogs to smell sick cows,” says Daigle. “I said I don’t know, but I can talk to dogs and we can tell.”

Smell tests

Diggle with a Ph.D. Student Aiden Juge and colleague Margaret Foster conducted a meta-analysis of 58 studies in which dogs were trained to detect diseases or health conditions in humans, other animals or plants.

In general, researchers note a high level of success in most studies, whether the scale used is sensitivity (the proportion of time they can detect a disease sample), specificity (the proportion of time they are unable to correctly select a healthy sample), or accuracy (the number of samples). which they can categorize correctly in general).

“Overall, the dogs did really well,” Juge says. “For all three metrics, we found that the average percentage was in the 1990s.”

Dogs trained to sniff out COVID-19 in Chile.

Source: Cesar Cortes, via Wikimedia Commons. Distributed under the CC BY-SA 2.0 license.

While the breed of dog does not appear to make a significant difference, differences in study design were notable and may have influenced the results. For example, specificity was higher in studies if the test was not double-blind (double-blind means that both the dog and its handler are unaware which samples are positive and which are negative). This suggests that dogs may read subtle cues from experimenters in tests that are not double-blind and the results are muddy.

Previous studies also differed in the type of disease to be detected, with lung cancer and prostate cancer being the most frequently studied conditions. The researchers found that disease type had an impact on detection, with greater success in cancer and bacterial conditions than in chronic diseases, such as seizures, sleep apnea and diabetes.

Jog says that the few studies they found related to chronic health conditions had inconsistent results. This may be due to the fact that the dogs in these studies were initially trained as medical alert dogs to focus on the specific scent of their handler. When testing their abilities on unfamiliar people, their accuracy can be affected.

“I would be interested in whether these dogs rely more on scent or familiarity with their handler’s body language,” Juge says.

A doctor’s best friend

Juge says dogs can be a useful tool to facilitate disease detection in settings that lack the resources or time to perform lab testing.

“Dogs are very good at screening a lot of samples quickly,” he says. “They can provide a good first-line screening test to identify individuals who may need more accurate lab tests. But we need more research to see how they perform in situations that closely mimic real-world scenarios.”

One of the situations where Daigle and Gog are interested in applying detection dogs is sniffing sick cows. The collaborator who came to Daigle with this question wanted to see if dogs could be trained to detect bovine respiratory disease, a condition that can be common in fattening cattle.

Daigle says that dogs have two characteristics that could make them ideal for this task. One is the undeniably acute sense of smell. The other is their cognitive and communicative abilities and their desire to work with humans.

Animal and Plant Health Inspection Service, National Detector, Dog Training Center, Harlee Trainee Dog Detector.

Source: USDA, public domain.

“Because cattle are a prey species, they are good at hiding their weaknesses or weaknesses, which can make it difficult to determine which species need help,” Daigle says. “But you can’t hide your body chemistry.

“Dogs can be a bridge between humans and livestock: we can communicate with them and they can pick up on olfactory cues from livestock that we can’t tell us what’s the right smell and what’s not.”

Daigle, Gog and his colleagues recently completed pilot study They trained two dogs to detect bovine respiratory diseases from cattle using nasal swabs. While the dogs showed some ability to distinguish between healthy and diseased specimens during training, they performed slightly better during testing than by chance. The researchers say the complexity of the task, including the additional “noise” from samples collected in the field, suggests that more tests are needed to determine if dogs can be an effective screening method for this disease. They are currently planning follow-up research to improve their methodology.

The results of Daigle and Juge’s pilot study confirm the conclusions they reached from their meta-analysis. Dogs are promising as disease detectors in contexts where more invasive screening is impractical or where a large population needs screening quickly and at low cost. But most evidence of their success is based on labs today. There is no information about the potential of dogs in real-world disease screening applications. More research is needed on when and how canine noses are best employed before disease detection dogs become a regular part of human or veterinary medicine.

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