Dogs have been taught to find a dozen diseases in people, and COVID-19 is the most recent one.
Dogs are well-known for being able to smell things. Because of their genes and bodies, they are perfect for sniffing. And for hundreds of years, people have used their great sense of smell to hunt, search, find drugs, explosives, and now even diseases.
Dogs have about 220 million smell receptors, while people only have 5 million. This means that dogs can smell things that we can’t even imagine. Dogs have smell receptors that are 10,000 times more sensitive than ours. This means that a single drop of liquid in 20 Olympic-size swimming pools is enough for a dog’s nose to pick up on the smell.
Smelling cancers
Dogs have such a fine sense of smell that they can pick up on even the smallest changes in hormones or volatile organic compounds that come from sick cells. Because of this, dogs have been trained to find signs of diseases.
Most people know that dogs can find cancer. They can be taught to smell different kinds of cancer, like skin, breast, and bladder cancer, by sniffing samples from people with cancer and people who don’t have cancer.
In a study done in 2006, five dogs were taught to use breath samples to find cancer. Once they were trained, the dogs could find breast cancer 88 percent of the time and lung cancer 99 percent of the time. They could do this at each of the diseases’ four stages.
The results could lead to new ways to check for cancer that are cheap, accurate, and don’t hurt people. As early detection gives people their best chance of staying alive, dogs could save a lot of lives.
Smelling other diseases
Dogs can also find many other diseases. One of them is malaria. Dogs were able to identify the smell of children with malaria parasites 70 percent of the time from the socks they had worn all night.
Dogs can also find Parkinson’s disease, as well as cancer and malaria. People would smell different even years before they developed Parkinson’s disease. So, dogs could be used to find the disease early and treat people before the symptoms get too bad to fix.
Dogs can tell if a person is about to have an epileptic seizure or a narcoleptic moment, for example. If you are in the wrong place at the wrong time, both can be dangerous.
In a 2013 study, two trained dogs used sweat samples to find 11 out of 12 people with narcolepsy. This shows that the disorder has a unique smell that dogs can pick up on. Biochemical changes in the body that lead to an attack are picked up by the dogs, and they help with different tasks to keep people from getting hurt. But most importantly, they can warn their handler up to 5 minutes before an attack, giving them time to move to a safe place or position.
A small study done in 2019 found that dogs could tell the difference between a general “seizure odor” and other smells.
More and more, diabetics are using their dogs to help them tell when their blood sugar level is dropping or going up. Isoprene is a natural chemical that can be found in people’s breath and that rises a lot when people have low blood sugar. People can’t smell the chemical, but researchers think that dogs can, which will allow dogs to be taught to tell whether their owner’s blood sugar is too low.
Migraines can also be predicted with a dog scan. Similar to how diabetic alert dogs can smell when their handler has low blood sugar, migraine alert dogs can pick up on the smell of serotonin, which goes up when the body is about to have a migraine. By letting their handlers know about the danger long before they might feel any symptoms, these dogs can tell them to take medicine to avoid getting sick.
COVID-19 and dogs
The coronavirus SARS-CoV-2, which caused the worldwide COVID-19 pandemic, is the most recent disease that dogs have been able to find.
In a pilot study, dogs were taught to recognize the smell of the COVID-19 disease. And in just a few weeks, the first dogs were almost as accurate as a standard PCR test at telling the difference between urine samples from COVID-19 patients and urine samples from healthy people.
It is still not clear what chemicals in urine cause the smell that seems to be typical of COVID-19. Since SARS-CoV-2 not only attacks the lungs, but also causes damage to blood vessels, kidneys and other organs, it is assumed that the patients’ urine odour also changes. Researchers are very hopeful that this is true because respiratory diseases like COVID-19 change the way our bodies smell, so it is very likely that dogs will be able to pick it up.
Another study included 1012 double-blind, randomised, and automated sample presentations. The average detection rate was 94%, with sensitivity ranging from 67.9% to 95.2% (average 82.63%) and specificity ranging from 92.4% to 98.9% (average 96.35%). With such a high detection rate, dogs can be trained in a short period of time to detect COVID-19 patients.
Dogs in the hospital? Not quite yet
Despite studies demonstrating that dogs can detect diseases, it may still take some time before they are used in laboratories to replace standard testing. Researchers still need to find out exactly what chemical compounds make dogs detect the presence of a disease. This is a problem both for better training of dogs that can sniff out diseases and for making machines that can more accurately detect cancer in its early stages.
If we knew more about what the dogs are picking up, their training could be made more consistent, but the medical community might still be skeptical. Not all doctors would trust a dog to tell them what’s wrong. More research may persuade doctors who are unsure about using them as part of the initial screening process to reconsider.