By Philip Myers
There is no doubt that dog-owners are prone to make crankish claims about their animals’ abilities to predict lottery numbers, or the outcome of a football match, or whatever. But in recent years their apparently bonkers assertions have turned out to be, in some cases, surprisingly close to the truth. In 1989 a paper was published claiming that ‘Dogs can be trained to distinguish patients with bladder cancer on the basis of urine odour more successfully than would be expected by chance alone.’ The research began when an owner pointed out her dog’s persistent interest in a skin lesion that later turned out to be a malignant melanoma. That such claims were taken seriously and opened a fruitful area of investigation provides yet another example of the weird ways in which breakthroughs in science often occur. Since then, the power of dogs to detect a number of different diseases has been shown experimentally, and they are now used to help diabetics monitor their sugar levels, and even to preempt narcoleptic attacks.
Malaria is the latest target of research, and Professor Steve Lindsay of the School of Biological and Biomedical sciences here in Durham has recently been awarded a prestigious Bill & Melinda Gates Foundation grant to look into the possibility of using dogs to detect infections. In conjunction with the charity Medical Detection Dogs, the London School of Hygiene & Tropical Medicine and the Gambian Medical Research Council Unit, his research, it is hoped, will be useful in the final stages of eradication of the disease, which caused almost half a million deaths globally last year. The problem is that when the number of infected individuals drops, the difficulty of detection using the normal invasive methods (such as collecting blood samples) increases, and the infection rate could easily rise again—a pretty grim cycle to be stuck in. Professor Lindsay, who has spent much of his career working on the eradication of vector-borne diseases, has explained that using trained dogs could allow large numbers of people to be screened easily, allowing relatively rapid detection and treatment of infected individuals. This research could play a key role in the drive to eradication, which would surely constitute one of the greatest public health achievements in history. I accept that this may seem a little over the top, but the grant wouldn’t have been awarded to a more prosaic project, with less at stake.
Ultimately, the basis of all this is the extraordinarily powerful sense of smell dogs possess, largely thanks to the hundreds of millions of smell receptors in their noses. For the sake of comparison, humans possess something closer to six million of these receptors. On top of this, they have many more different types of receptors, meaning they experience smells that we don’t even know exist. And on top of all of that, there are many specific physiological adaptations that enhance these remarkable abilities. It has been suggested that they have wet noses to help trap transient molecules for better smell detection. They can also smell in stereo, allowing them to locate the origin of a scent more precisely—a rare kind of navigational tool. And while we breathe in and out through our disappointingly simple nostrils, dogs exhale exclusively out of the side of theirs (that is, through the side slits that any dog-owners among the readership are probably aware of), creating turbulent air patterns that draw new odour molecules into the front of the nostrils. Even the olfactory bulb of the brain is, in relative terms, many times larger in dogs than in humans. That millions of years of evolution have produced these extraordinary and beautiful adaptations is remarkable enough. That we may be able to use them to help eradicate the deadliest disease ever known is even more astonishing, as far as I’m concerned.
Photograph: public domain via Pixabay