The term "man's best friend" is commonly used when it comes to dogs, and it is not hard to understand why. The loyalty of a dog toward its owner is something that cannot be questioned. But in recent years, the tables have turned and humans have become more reliant on dogs than ever before - to help save lives.
According to The Humane Society of the United States, there are around 83.3 million owned dogs in the US alone, showing that America is clearly a nation of dog lovers. But do we underestimate the talent of these amazing creatures and see them purely as pets?
In recent years, organizations all over the world have looked to training dogs to detect medical conditions in humans.
Earlier this year, Medical News Today reported on research from UK charity Medical Detection Dogs detailing how dogs have the ability to alert their diabetic owners when their blood sugar levels are too low (hypoglycemic).
Other research has revealed how dogs are able to detect clostridium difficile bacteria - a component that causes many hospital-acquired infections - in feces samples and hospital air.
But how exactly are dogs able to detect human disease?
All in the scent
A dog has around 125 to 300 million scent glands, while a human has around 5 million scent glands. This means a dog's sense of smell is around 1,000 to 100,000 times more sensitive than a human's.
A dog's sense of smell is 1,000 to 100,000 times more sensitive than a human's, making them the perfect candidates for sniffing out human disease.
It is a dog's intricate sense of smell that has captured the interest of the medical world in using these animals to help detect human diseases and to help people who suffer from these diseases live a more fulfilling life.
Dogs4Diabetics is a US organization founded in 2004 that researches, trains and places medical assistance diabetic alert dogs with insulin-dependent diabetics.
Ralph Hendrix, executive director of Dogs4Diabetics, told Medical News Today how dogs are able to detect hypoglycemia in diabetics.
"We believe all diseases have scent associated with the diseases, due to the changes occurring within the body, with different organs expressing different chemical compounds. These scents are evident in breath and sweat," he explained.
"Dogs have highly sensitive senses and can learn to recognize symptoms from many types of disorders. In our work, they are not taught to react to symptoms, but to scent."
But of course, these dogs do not automatically adapt to detection of these scents. A great deal of training goes into ensuring they acquire the correct smell to carry out their job.
Train to gain
According to Hendrix, the dogs they train must meet a set criteria in order to become medical detection dogs.
"The criterion ranges from their behavior characteristics, their relationships with humans (ability to bond and willingness to please), their environment soundness, to their work ethic, motivations, response to reward, etc."
Dogs4Diabetics uses breeds that have been raised and socialized to take part in service work. The dogs they use are donated to them by Guide Dogs for the Blind of San Rafael and Canine Companions for Independence of Santa Rosa, both in California.
Hendrix says that the dogs donated to them are primarily Labrador retrievers and golden retrievers, or a mix of the two breeds.
"Other breeds may work, but these breeds are well accepted for service work because of the temperament and disposition to work with their human companions," he told Medical News Today.
Explaining how dogs can be trained to sniff out hypoglycemia in diabetic patients, Hendrix said the dogs are trained on a scent collected from a diabetic's breath or sweat when they are experiencing hypoglycemia:
"That dog is trained to identify the hypoglycemic scent and then is taught to discriminate the hypoglycemic scent from other attractive, but distracting, scents through a series of games and training exercises. The dogs receive positive rewards for identifying the correct scent and for their work."
Hendrix added that it takes some time to train a dog to make the transition from "scent discrimination training" to detecting actual hypoglycemia on a diabetic in a home environment.
"All diabetics will have residual scent around from previous hypoglycemic episodes. This 'dead' scent lingers in their home, their clothes, their bed. The dogs have to learn to differentiate the 'dead,' lingering scent from the 'live' scent, and transition their alert to only the live scent for which they are rewarded."
Hendrix added that the dogs also have to be trained to identify and alert on the hypoglycemic scent within different environments, such as work, at school or in the car.
Dogs could be the future of cancer detection: a device called Na-Nose™ that can smell lung cancer compounds is based on a dog's sense of smell.
"To the dog, it is simply a game with positive rewards that is played everywhere," he added.
Hendrix explained that Dogs4Diabetics' clients also receive extensive training, including how to respond to the dog once it alerts them that there is a problem with their blood sugars. The owner must be sure that the dog is accurate in their alert by testing their blood sugar levels with a glucometer to confirm there are any changes.
Potential for cancer detection
It is not just hypoglycemia that dogs have the ability to sniff out. Continued research is looking at the use of dogs to detect various types of cancer - named "bio-detection dogs."
Earlier this year, Medical News Today reported on a study detailing how researchers are looking to create a breakthrough method of using dogs to detect ovarian cancer.
The researchers explained that the dogs are able to detect volatile organic compounds (VOCs), or odorants, that are altered in the early stages of ovarian cancer.
A 2011 study conducted by researchers at Medical Detection Dogs also found that these VOCs could be biomarkers of bladder cancer.
Using four trained sniffer dogs to analyze urine samples from patients who had bladder cancer, alongside healthy controls, the researchers found that the dogs' specificity in detecting the cancer ranged from 56% to 92%.
A video from Medical Detection Dogs explaining how bio-detection dogs are able to detect scents of cancer and other diseases can be viewed below.
Previous research has also found that dogs may be able to smell volatile organic compounds from a patient's breath sample - as these compounds may appear on the breath in the early stages of cancer.Explaining how the bio-detection dogs are trained to sniff out cancer odors, Rob Harris, bio-detection manager at Medical Detection Dogs, told Medical News Today:
"We condition the dog to the volatile pattern of a cancer sample with the use of an audible sound, such as a clicker. The clicker is associated to something the dog enjoys. For example, a treat or toy.
The clicker signals to the dog that the last behaviour carried out before the click was correct and he will receive his reward. Over time, the dog learns that the click only appears as he sniffs at a cancer sample."
From this ongoing research, investigators have even started creating devices that may detect cancer by "mimicking" the sensitivity in a dog's nose.
The Na-Nose™ - created by researchers at the Technion-Israel Institute of Technology and Alpha Szenszor, a carbon nanotube manufacturer in Boston, MA - is a device that can analyze more that 1,000 different gases in the breath in order to detect lung cancer. In clinical trials, the device has been found to have up to 95% accuracy.
'Dog fakers' putting people's health at risk
But regardless of numerous studies providing evidence that dogs are successful in detecting cancer among other human diseases, there is no doubt that some may have reservations with regard to the dogs' accuracy in identifying diseases.
Hendrix told Medical News Today that a dog's detecting ability is dependent on the training they have received and whether they have been trained to the required standards.
"I see no problem in using trained dogs with a proven ability to assist in the detection of the possible presence of a disease.
If the dog can identify the risk of its presence in the fashion that it has been trained with the known level of reliability, then I believe that the possibility exists that there is a problem, even if current technology does not immediately confirm the risk. The person should be followed more intently for the prospect of its appearance."
However, Hendrix noted that there are some dog training companies out there that are not providing the correct training needed to ensure their dogs are fully qualified medical detection dogs, and are therefore putting clients' health at risk.
"We are particularly concerned over cases where people are selling puppies and rescued dogs with purported hypoglycemic alerting skills to be used with diabetics and for public access," he said.
"It is impossible to imprint a puppy with a scent and then expect it to be a reliable and consistent alerter over its lifetime. But people are paying $20,000 or more in a desperate attempt to obtain a 'trained' dog."
Hendrix said there are also cases where pet dog trainers attempt to train service dogs or medical assistance dogs, but they do not have the relevant training or background.
"We are appalled when we hear of trainers or diabetics who are willing to put the life of their child or a loved one in the safety of a dog that has not been properly trained, certified, or without sustained training and ongoing support from experts," he added.
The future for medical detection dogs
There is no doubt that over the years, dogs have become more than just our pets. They have become companions that help save lives.
The first diabetic hypoglycemia alert dog in Britain is a Labrador called Zeta. One of Zeta's owners, Angela, says she looked to Medical Detection Dogs for a hypo-alert dog that could help with the management of her husband's diabetes.
"The first time Zeta alerted, I became very emotional and cried because I did not really believe that alerting was possible. At first we thought she was making errors, then I realized that she was catching highs and also rapid drops in his blood sugar levels," says Angela, speaking to Medical Detection Dogs.
"We really don't know what we would do without her: she is worth her weight in gold!"
Emphasizing the benefits of these animals, Rob Harris, from Medical Detection Dogs, added:
"The real value of the dog comes with his ability to detect changes so early giving the client the opportunity to treat themselves, preventing paramedic callout and hospital admission. The assistance dog can accompany his partner everywhere, increasing confidence, independence and improving wellbeing."
According to Hendrix, the challenge is to provide "consistent, provable and reliable" training in order to make use of the dog's astounding senses so they can provide support to their human companions.
"Dogs are dogs, they cannot tell us what they scent, and trainers and handlers have to devise ways to both train the dogs and then validate the accuracy of their response to that training. They have to reinforce that training over the working life of the dog to sustain the skill. It can be done and there are protocols and processes that validate these skills."
So what does the future hold for bio-detection and medical detection dogs?
Dogs4Diabetics founder Mark Ruefenacht says he believes we have only "scratched the surface" in what a dog can do to assist with various medical diagnosis and the management of chronic diseases and disabilities.
"The oft-heard, 'human-animal bond' has so much potential in the way we move forward in our working relationships with dogs," he adds.