Recently, in an article in the New Republic, ‘The Animals That Can Save Your Life’, journalist Emma Young introduces readers to the emerging science of training animals to detect things humans cannot. Having a powerful sense of smell can be very important in nature. Scent can signal food, danger, or the opportunity to mate. Some animals mark their territory with scents while others use them to lure prey. Bees, moths, ants, and other insects communicate largely through the use of pheromones. The average human has 6 million smell receptors, a tiny amount when compared to a bloodhound with more than 300 million. Moreover, the percentage of a dog’s brain responsible for processing scents is over 40 times that of a human brain. For evolutionary reasons, many animals possess a sense of smell that is far more powerful and specialized than a human’s.
African pouched rat (Courtesy: Wikipedia)
Young’s story explores what happens when humans work with animals and utilize their powerful sense of smell to perform valuable tasks. In the article, she follows scientists in Apopo, Tanzania, who have trained African pouched rats to detect everything from tuberculosis in human samples to buried landmines.
So far, the only disease that rats are trained to detect is tuberculosis. That’s impressive, but there are some other animals with useful noses, too.
Mice are naturally color blind and have a poor sense of vision, which they make up for with a keen sense of smell used to detect food, danger, and potential mates. Scientists have been studying mouse noses for a while to see if they could be put to practical use. In 2002, researchers at Monell Chemical Senses Center trained mice to detect the smell of mouse mammary tumor virus. Next, in 2010, Monell scientists trained mice to detect the odor of bird flu infection in the droppings of ducks. The most recent breakthrough came early in 2016, when researchers were able to train mice to distinguish urine samples between mice with the genes for Alzheimer’s and those without the genes. This work may help lead scientists to new biomarkers for the disease.
Mouse being trained to detect bird flu (Courtesy: Maryanne Opiekun, Monell Chemical Senses Center)
Fruit flies, while small in stature, have oversized scent receptors. Researchers in Rome, Italy, were able to use the fly’s olfactory system to identify not only the presence of cancer within cells, but different groupings among the cancer cells. Researchers genetically modified fruit flies to make their scent receptor neurons glow when activated. Cancerous samples activate specific patterns of neurons and different cancers activate slightly different patterns. Thus, scientists can check a sample by looking at which neurons are glowing. This work was a result of a collaboration between biologists and electronic engineers – an area that may yield future electronic detection products.
The New Republic story also covered how dogs can smell hypoglycemia, proteins linked to peanut allergies, and even detect when a person with postural tachycardia syndrome is about to fall unconscious – all skills that could help people living with these medical conditions. Dogs are perhaps the most skilled of the cancer-detecting animals. They can detect breast, bladder, colorectal, ovarian, and prostate cancers. Research is currently underway at the University of Manchester to determine whether dogs can be trained to recognize the scent of Parkinson’s.
Video: New prototype device to allow dogs to detect cancer in humans (Courtesy: Open University)
Research into animals’ abilities to detect human conditions and diseases is quite new. As scientific methods progress and interest in the field increases, we will likely see other applications of animals’ senses of smell. Once again, animals work in partnership with humans to identify and treat disease.