They perceive glycosaminoglycans whose presence in blood and urine has, according to researchers at Karolinska Institutet, a specificity of 95% for various types of tumors including breast, prostate and lung
It has long been known that dogs, especially Labradors, Newfoundlands, Dalmatians and Saint Bernards, know how to smell diseases, in particular certain tumors (such as those breast, prostate or lung) before they give rise to clinical manifestations. But what do they smell? The answer could come by chance from a study of 1,260 subjects published on PNAS by Swedish researchers from Karolinska Institutet directed by Sinisa Bratulic: they were looking a non-invasive method for early detection of cancer from urinewhose smell allows dogs to perceive not only the presence of tumors, but also that of diabetes or the arrival of an epileptic, migraine or narcoleptic attack a few hours in advance.
Swedish researchers were able to identify 14 different types of cancer early based on the concentration of glycosaminoglycans (acronym GAG) which are normally part of the extracellular matrix of the tendons to which they confer, together with elastin and collagen, elastic properties which allow them to stretch. These polysaccharides are early altered by tumors by breaking down in blood and urine: by searching for them also in plasma, the Swedish researchers managed to obtain a sensitivity of the test between 41.6 and 62.3% and a specificity of 95% for tumors still in the first stage, a diagnostic accuracy that is double that of any other method available today. What smell do glycosaminoglycans have to be perceived by dogs? Evidently for us they are odorless, but not for our four-legged friends whose sense of smell has 150-300 million cells depending on the racewhile humans have only five with a brain area for odor recognition of about five square centimeters, compared to a dog’s 150.
One more brain
Last summer a study by researchers from the Universities of New York and San Francisco directed by Philippa Johnson, published in the Journal of Neurosciencediscovered a network of five nerve connections we are missing extending from the canine olfactory bulb directly to other areas of the brain: occipital lobe, cortical spinal tract, limbic system, piriform lobe, and entorhinal cortex. It explains how the dog can integrate olfactory stimuli into its cognitive functioningso that smells become an open book for him.
Not just cancers
There are now many reports that indicate that dogs are able to perceive the smell of certain diseases: for example diabetes or blood sugar disturbances. On the other hand, the famous doctor Thomas Willis of the 1600s used taste instead of smell, because by tasting the urine of diabetics he was the first to discover that their urine was extraordinarily sweet, as if it contained sugar or honey. However, dogs smell blood sugar alterations even before diabetes sets in and warn their owners with anomalous proximity-seeking behaviorsas if they perceived that they need to be looked after.
Sweat and breath
The most surprising thing is that also perceive the imminence of the attacks of diseases such as migraine, epilepsy or narcolepsy
for which no clinical trials are yet available. Evidently in this case, instead of urine, dogs perceive in sweat and breath the increase in markers of stress induced by the arrival of attacks, as discovered by a recent Irish study published in PLOSONE.
Their ability to smell odors that are imperceptible to us makes them precious in all situations in which the sense of smell is essential, such as the search for survivors of natural disasters or in drug operationswhere the police multiply their skills with the help of dog and veterinary educators using the so-called positive reinforcement method, which rewards the recognition of a certain smell.
January 17, 2023 (change January 17, 2023 | 19:51)
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