Dogs are often described as man's best friend. A dog will always be there at the beginning of a day to greet you, there in the evening to welcome you home with a frantically wagging tail and help to make you feel better when you're feeling down. Dogs become, to many people, a member of the family. But not only do they help to make a grey day brighter, many can also be trained to help save lives and aid us in tasks with their supreme sense of smell. Sniffing cancer is just one example of this.
How does your dog smell?
Have you ever noticed how a dog will always seem to come running when you have a biscuit tucked away somewhere? This is because the olfactory, or smell system of a dog is highly advanced and is sensitive to a far greater number of smells than people can detect.
Dogs' noses also function rather differently than our own. When a dog inhales, a fold of tissue within their nostril helps to separate the air into two different pathways with contrasting functions; some goes to the lungs for breathing, while the rest is used primarily for smell. The air used for smell is directed to the turbinates, an area of densely folded tissue, which contains thousands of different olfactory receptors . It is here that the receptors bind to specific air particles based on their size and shape, fitting like a lock and a key. This complementary match triggers an electrical signal, which is sent to the brain for analysis. In this way the dog can begin to process what they are smelling - whether it's a well-hidden biscuit, or something more sinister, such as drugs or explosives.
Putting that nose to good use
Dogs are used extensively for security purposes, commonly seen at airports, football stadiums and other high risk areas; deterring criminals and also identifying suspicious items in the vicinity. Dogs are also frequently trained as aids for the handicapped, for example guide dogs, which dutifully guide their visually impaired owners and enable them to live a more active life., Dogs have recently started to be trained to put their superior senses to good use in order to sniff out deadly human illnesses.
According to some medical practitioners, certain diseases are associated with a distinctive scent, with respiratory conditions within the lungs affecting the smell of the sufferer's breath, and other illnesses affecting a sufferer's sweat or urine. These signs tend to be subtle and hard for humans to detect, but it would appear that what humans cannot smell, other animals can.
Diabetes-sniffing dogs already exist, trained to detect when their diabetic owners have low blood sugar levels from smelling their breath, in which case they can warn them and fetch help .
Cancer is yet another disease which is thought to give off a scent. According to a Cancer Research Statistics report, around one in four people in the UK die as a result of cancer . It is therefore of utmost importance that diagnostic tests are effective in order to catch the disease before it can spread and grow too large to treat. Sniffer dogs may be a new novel way to do this...
So what exactly is a dog detecting?
There have been many anecdotal stories from around the world where dogs have repeatedly seemed to 'warn' their owners that something is wrong, by licking, scratching or staring at the affected area. Spurred on by their pet's unusual behaviour some owners have discovered, upon medical testing, that they have cancerous cells. This early detection has saved numerous lives, and was what inspired scientists to begin proper scientific research back in 2004 .
Dogs are thought to be using their highly advanced smelling systems to detect volatile organic compounds - volatile meaning they are given off as a gas and organic meaning they are produced within the body - generated by malignant cancerous cells. Malignant cells which rapidly divide and expand in size, undergo protein changes which leads to the fracturing of the cell's membrane, which acts as a sort of envelope. When this envelope, composed of lipid fats, is broken down, volatiles can escape and be detected.
Now, organisations such as Medical Detection Dogs, based in Milton Keynes, UK, are training dogs to sniff out forms of this life-threatening disease.
How does the training process work?
Unsurprisingly - using a lot of biscuits. Dog breeds are selectively chosen for characteristics such as a predisposition for searching and locating using scent and being highly motivated by either a food treat or a tennis ball reward. These working breeds tend to be Spaniels or Labradors, chosen for their ability to find and retrieve.
The training works using the fundamental principle of delivering a reward when the dog successfully identifies a cancer sample. This is an example of positive reinforcement, where the dog associates the act of finding a sample with a particular smell with a treat.
The dogs are trained to screen samples of either a patient's breath or urine, depending on the form of cancer . The training process uses a carousel system, where the scent samples are held in small pots - some are from healthy individuals and one will be from an individual suffering from cancer. When urine is used, only 0.5ml of the liquid is required - a tiny amount that proves no problem for the dog's highly sensitive sense of smell. Dogs are walked round the carousel and when they find the correct target, they give an indication such as "sit" or "stand", and are then rewarded.
The dogs are able to detect a whole range of cancers, including prostate cancer which is the most common form in men within the UK, with over 40000 new cases diagnosed every year .
Research studies have shown that dogs are extremely accurate, and have low rates of false-positives. For example in a 2011 study published in European Urology, a dog successfully distinguished between prostate cancer samples and healthy samples in 30 of 33 cases - an accuracy level of 91% .
Will we start seeing 'dog-doctors'?
There are two ways in which the dogs are going to make a monumental difference in the future. Firstly in the short-term, they can provide secondary screening for cancers that can be difficult to diagnose, such as prostate cancer. Multiple diagnostic techniques will provide greater reliability.
Secondly, as it would be impractical to provide every doctor's surgery in the country with their own dedicated dog, research is ongoing involving the development of an electronic nose, an 'e-nose', stemming from the dog's work. If cancer is detected at an early stage, before it's had the chance to grow larger or to spread to other parts of the body, it can be treated more easily and effectively. E-noses provide a cheap, non-invasive and reliable way of diagnosing cancer early, giving patients the best possible chance of survival. Better yet, they don't need to be fed or walked!
But how do e-noses work? These electronic systems work in the similar way that the nose does, picking up scent molecules when a patient breathes into a tube.
In one type of device, the sensors analyse over 1,000 different gases that are contained in the breath to identify those that may indicate that something's wrong. Gases of interest - ones associated with the disease - bind to sensors within the system, much like the receptors in our noses, which then transmits an electrical signal to indicate a match.
Another odour sniffing device uses the exhaled air from the patient and checks for matches of 'bio-markers' against known profiles for breast cancer recorded in a database . This could reduce the need for mammograms which many women find an unpleasant experience.
Research into e-noses has been carried out since the 1980's and prototypes currently exist that have 80% accuracy . The aim for E-noses for hospital use is to be small, transportable and inexpensive. Surgeries around the world, including in developing countries, could be equipped with an e-nose device that could be used as part of a routine examination. Results are rapid, coming through in minutes, instead of weeks, allowing medical practitioners to react and set treatment into action more quickly. There are even ideas that in the far-off future that it can be developed into an application - an 'app' for our phones and tablets. Simply breathe onto your phone, and sensors embedded into the device will alert you as to whether you should consult a doctor.
"A dog is the only thing on earth that loves you more than he loves himself" - Josh Billings
It would appear that our clever canines have the potential to help save lives. So the next time your dog causes some mischief, remember that one day, they might just save your life.