A dog’s nose knows, and it might just know when you’re emitting the scent of infectious disease. With its 300 million scent receptors, the dog’s most recent detective work involves COVID-19.
Dogs are identifying COVID-19 cases in airports
You might have seen the many news stories about dogs sniffing out COVID-19 at the Helsinki airport and at airports in the UAE. It takes about 10 seconds per sample. And the best part? No nasal swabs needed.
The test works using sweat collected on wipes from the neck of arriving passengers. The wipes then get left in a box and make their way into the testing room. There, the dog trainer puts wipes into individual samplers where the dogs sniff and signal a positive test either by sitting down or stopping at the sample. The dogs detected both asymptomatic, infected individuals, and pre-symptomatic individuals. The pre=symptomatic stage is an earlier stage than a PCR test would be able to detect.
The dogs aren’t detecting the virus itself, but rather, they’re sniffing out volatile chemicals that are released by a person’s body that are unique to infected individuals.
Another study using saliva instead of sweat showed that dogs can correctly identify positive COVID samples 83% of the time and negative samples 96% of the time.
Fortunately, dogs are not easily infected and there’s no evidence that dogs develop symptoms from testing nor can they pass virus to other people or animals.
But before COVID-19, dogs were already sniffing out disease in preliminary studies. Let’s take a look at a few examples.
Dogs detect malaria infections from socks
People infected with malaria parasites have a distinct odor compared to those that are uninfected. In fact, mosquitos respond to specific aldehydes that are given off in greater quantities in malaria-infected individuals and preferentially feed on asymptomatic, malaria-infected individuals. So could a dog be trained to detect malaria infections in people?
Short answer. Yes.
The medical journal, The Lancet, describes a study where 30 children with asymptomatic malaria infections and 145 uninfected children wore socks overnight that were then collected for the dogs to sniff out. The found that dogs, albeit only two dog from the study, could distinguish
h between asymptomatic malaria-infected and uninfected individuals.
Dogs smell the difference between Pseudomonas aeruginosa from other bacteria pathogens in culture
Pseudomonas aeruginosa infections are common in cystic fibrosis patients, chronically infecting ~60% of patients by adolescence or adulthood. Historically, the most reliable techniques for detecting P. aeruginosa lung infections are too time consuming and invasive for regular testing. While scientists have developed tests that use breath sampling for detection, they’re not very sensitive.
So how about sniffer dogs? P. aeruginosa has a natural odor that dogs could be trained to detect. Researchers tested four dogs and found that these dogs could distinguish P. aeruginosa from other bacteria in culture. This research is just the beginning of using dogs to detect P. aeruginosa infections. The researchers envision a future where cystic fibrosis patients can send samples of breath, cough, or exhaled breath condensate to a testing center where dogs can identify the bacterium from afar.
Dogs sniffing out Clostridium difficile? Maybe
Between 2012 and 2017, scientists published three papers on a dog’s ability to detect Clostridium difficile in stool (links here and here) and on medical equipment. C. diff is a bacterium that causes recurrent diarrhea and ~30% of cases are transmitted in the hospital. These studies seem to point towards the dog’s ability to detect C. diff. However, each study documented the results from a single dog. How would the researchers know if this ability varied between dogs or the degree of variation?
A subsequent study used two dogs to sniff out C. diff, however, found inconsistencies between the two dogs’ ability to correctly detect disease, calling into question the reliability of the previous studies. However, there are a few caveats to the study: (1) the experiment used refrigerated stool, rather than fresh stool, (2) out of the samples, few were positive samples which limits how well the researchers could measure sensitivity and specificity, and (3) the study only included two dogs. For now, the researchers suggest sticking with improving C. diff molecular diagnostics.
