Dogs can sniff out all sorts of things, as every dog owner knows. At the dog park, Cracker, my Bedlington terrier, unfailingly finds all the dog owners who have treats in their pockets. I was privy to a more, uh, interesting illustration of canine olfactory skill some years ago...
When I fly back to the U.S. after a trip abroad, I'm always so eager to get back to Cracker that I can't resist scratching and petting the USDA beagles at U.S. Customs, in spite of the "DO NOT PET" message on their vest. The handler is invariably annoyed and admonishes me. Well, one time, the dog got her scratch, then moved to my backpack and sat down – the signal for detection of contraband. There was a long-forgotten banana at the bottom. That earned me an intensive inspection of all my luggage. (I do not recommend this.)
The ability of dogs to sniff out explosives, illicit drugs, and forbidden produce is well known, but there have also been some successes in getting them to detect various disease states. For example, diabetic-alert dogs are trained to sense certain volatile organic compounds (VOCs) that indicate high or low blood sugar in a diabetic's breath or sweat. When the dog detects the characteristic odor emitted by the person, he (or she) alerts with a specific trained behavior such as pawing, sitting, or barking.
There are numerous case reports of dogs spontaneously detecting and calling attention to human cancers, including skin and breast; and in various lab (no pun intended) experiments with human tissues and fluids, dogs have been trained to detect a wide array of cancers.
A fascinating ongoing project is a California-based pilot program to train dogs to detect COVID-19 infections in humans. After two months of training on COVID-19 scent samples in the laboratory, the dogs achieved greater than 95 percent sensitivity (the test's ability to correctly designate a positive) and specificity (its ability to correctly call a negative) for detection of the virus. The dogs' performance in real-world conditions was then tested in the field: 50 visits were conducted at 27 schools from April 1 to May 25, 2022 on 1,558 participants.
The screenings were performed on days when antigen testing was scheduled. The children were lined up standing six feet apart with their backs to two yellow Labradors – Rizzo and Scarlet — led by handlers. One by one, the dogs sniffed each student's ankles and feet. To indicate a "COVID-positive," a dog would sit down before moving onto the next person, similar to how the USDA dog signaled finding my illicit banana.
The investigators assessed the dogs' sensitivity and specificity for COVID-19 infection, using antigen test results as the comparator. If a dog signaled positive and the antigen testing results were negative, the signal was considered a false positive; conversely, if a dog did not signal and the antigen testing results were positive, that was counted as a false negative.
The dogs did very well. In the field studies, their sensitivity of detection was 83 percent, with specificity of 90 percent.
The ultimate goal is to have dogs able to perform large-scale, non-invasive COVID screening, with antigen testing necessary only for verification on persons with positive dog screening results. That would reduce significantly the number of antigen tests performed.
Sounds good to me. I'll bite.
A postscript: With COVID testing in schools now infrequent, Rizzo and Scarlet have turned their noses to detect COVID in California nursing homes.
Henry I. Miller, a physician and molecular biologist, is the Glenn Swogger Distinguished Fellow at the American Council on Science and Health. He was the founding director of the FDA's Office of Biotechnology.