Man’s best friend — and medicine’s too?

For as long as dogs have been domesticated, humans have relied on them for companionship and their remarkable sense of smell. Dogs and their super sniffers help humans hunt; track criminals; and detect guns, drugs, or explosives in airports. Now scientists are investigating whether dogs can also help sniff out diseases before humans know they have them.

Scents and scent-ability

A dog’s keen sense of smell outranks ours many times over. For example, dogs’ brains devote more real estate to analyzing scents than ours, their noses have 60 times the number of scent receptors as ours (about 300 million versus our five million), and their smell accuracy is far more precise than ours. “Dogs have exquisitely sensitive noses and can detect molecules in the parts-per-trillion range. Humans, in contrast, typically detect odors in the parts-per-million range,” says Dr. Sophia Koo, an infectious disease specialist at Harvard-affiliated Dana-Farber Cancer Institute.

In theory, then, dogs should be well-suited to picking up odors generated by bacteria or diseased human cells. These organisms and cells produce molecules with distinct and often subtle scents that come out in our breath, body fluids, skin, or bowel movements. As the molecules evaporate in air, they become detectable.

For example: “We know there are molecules associated with prostate cancer that can seep into urine, and presumably they should be detectable with sensitive enough techniques,” says Dr. Paul L. Nguyen, a radiation oncologist at Dana-Farber Cancer Institute.

Dog ownership: Just what the doctor orderedOwning a dog has many health benefits. Studies have shown that, compared with people who don’t own dogs, dog owners walk more, have lower blood pressure and stress levels, eat more healthfully, and have more success losing weight — in part, because of the activity necessary to walk the dog.The unconditional love and companionship dogs provide also works wonders for our emotional health, helping to stave off loneliness (which is associated with an increased risk for chronic disease and even an early death) and offer an additional sense of purpose in life: to return the love your dog so freely gives you.

Teaching dogs new tricks

For decades now, scientists have been studying whether dogs might be able to detect many types of illnesses, using their superior sense of smell.

Cancer. Dogs have been studied for their ability to detect lung, skin, breast, and bladder cancer, with mixed results. Scientists are now looking at whether the animals can sniff out colorectal and prostate cancer — with promising results. “Some of the dog studies about prostate cancer have been extremely impressive, with 90%-plus accuracy,” Dr. Nguyen says.

Infection. In small studies, dogs have had some success identifying urinary tract infections in people of all ages, and malaria in children. Dogs have correctly identified the dangerous diarrheal infection Clostridioides difficile in many studies.

Also exciting are current efforts around the world to see if dogs can smell COVID-19 in humans. In one small randomized trial, published online July 23, 2020, by BMC Infectious Diseases, dogs were able to discriminate between samples from infected and uninfected people with high accuracy: the dogs identified about 83% of positive cases and 96% of negative cases. (The COVID virus in the test samples was killed before the detection dogs were exposed to them.)

Other diseases. Dogs are also being studied for their potential ability to smell Parkinson’s disease as well as narcolepsy (sudden episodes of deep sleep). And pooches are already being used as service animals to alert people with diabetes to high or low blood sugar levels. However, using dogs for this purpose has been controversial because of an unregulated industry and claims of fraudulent dog trainers.

Is it really paw-ssible?

Even though studies of medical detection dogs have been encouraging, the reality of using the animals beyond lab settings has big obstacles.

One is that it’s hard to get solid evidence about accuracy. “Dogs have an outstanding ability to detect disease odors, but it requires intensive training of even a single dog to discriminate disease from non-disease well. Even between dogs, there is variability in how well they can ultimately distinguish states of disease,” Dr. Koo says. “There are also confounders, as dogs can easily be distracted and falsely call a signal or miss a signal when distracted.”

Also, using medical detection dogs in the real world may be unrealistic. “The concept of massive numbers of dogs professionally screening urine [or other types of] samples just doesn’t pass the sniff test; it’s impractical and instead will need to be done with laboratory devices to make it scalable and acceptable,” Dr. Nguyen says.

Accordingly, scientists — including Dr. Koo — are testing machines that may be able to detect disease scents. “I think sophisticated scent detectors will come into use for the diagnosis of certain diseases and that this is not just a flash in the pan,” says Dr. Koo. “There is a lot of potential in this area; this is why a lot of the research in my own laboratory is dedicated to identifying the molecules that reveal different types of lung infections, so that we can build machines to detect them.”

And researchers know such technology has a lot to live up to. “We still have a way to go,” Dr. Nguyen says, “before we can replicate what nature has done so elegantly with the canine sense of smell.”

Bible verses for today’s meditation and inspiration: Matthew E. McLaren

2 Chronicles 7:16 “For now I have chosen and consecrated this house that My name may be there forever, and My eyes and My heart will be there perpetually.

2 Corinthians 9:10 Now He who supplies seed to the sower and bread for food will supply and multiply your seed for sowing and increase the harvest of your righteousness;

Hebrews 5:12-14 For though by this time you ought to be teachers, you have need again for someone to teach you the elementary principles of the oracles of God, and you have come to need milk and not solid food. For everyone who partakes only of milk is not accustomed to the word of righteousness, for he is an infant. But solid food is for the mature, who because of practice have their senses trained to discern good and evil.

1 Peter 2:2 like newborn babies, long for the pure milk of the word, so that by it you may grow in respect to salvation,

Luke 8:14-15 “The seed which fell among the thorns, these are the ones who have heard, and as they go on their way they are choked with worries and riches and pleasures of this life, and bring no fruit to maturity. “But the seed in the good soil, these are the ones who have heard the word in an honest and good heart, and hold it fast, and bear fruit with perseverance.

Matthew 13:22-23 “And the one on whom seed was sown among the thorns, this is the man who hears the word, and the worry of the world and the deceitfulness of wealth choke the word, and it becomes unfruitful. “And the one on whom seed was sown on the good soil, this is the man who hears the word and understands it; who indeed bears fruit and brings forth, some a hundredfold, some sixty, and some thirty.”

Mark 4:19-20 but the worries of the world, and the deceitfulness of riches, and the desires for other things enter in and choke the word, and it becomes unfruitful. “And those are the ones on whom seed was sown on the good soil; and they hear the word and accept it and bear fruit, thirty, sixty, and a hundredfold.”

2 Corinthians 9:10 Now He who supplies seed to the sower and bread for food will supply and multiply your seed for sowing and increase the harvest of your righteousness;

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