DOCTORS WANT TO SMELL DISEASE
Sick or healthy? Soon, doctors will make diagnoses by having an electronic nose sniff at our breath. New scientific research links specific smells to different diseases, and we can even smell some of them ourselves.
You might think your sense of smell just stinks, but medical science is starting to discover “electronic noses” work really well.
Joy Milne, a retired nurse, carefully smells at a sweaty white T-shirt. She is searching for a special tree and musk-like body odour, which she noticed the first time in connection with her husband, who suffered from Parkinson’s disease. When she has determined whether the owner of the T-shirt is ill or healthy, she gets another T-shirt. And so, the experiment goes on, until she has smelt 12 T-shirts, of which six have been used by Parkinson’s patients and the rest by a healthy control group. Milne’s sensitive nose places all the T-shirt owners in the right categories – except from one person from the control group, whom she diagnoses to be a Parkinson’s patient.
The simple experiement, which was carried out at the University of Edinburgh, has helped scientists find out how diseases might be diagnosed in the future. Today, most final diagnoses are made based on samples of bodily fluids or tissue taken from the patient’s body, and the methods can be both expensive and physically demanding for the patient. If the odours that our bodies give off all the time can be captured and analysed to determine what is wrong with us, it will be possible to make diagnoses much earlier and more easily, without any inconvenience for the patient.
The experiment with Joy Milne shows that we have a surprising ability to smell disease, but if smell is to be used as a real diagnosis tool, scientists must find out exactly which smelling molecules the body emits in connection with individual diseases. For this purpose, Israeli physician Hossam Haick has developed an electronic nose that detects and analyses the volatile organic compounds, VOCs, that cause most smells. By making the electronic nose smell people’s breath, Haick has so far diagnosed 17 different diseases – including breast cancer, schlerosis, and several intestinal conditions.
Every disease has a smell
Hossam Haick’s electronic nose has identified a wealth of volatile organic compounds, which previous research has already linked with diseases, but so far, the challenge has consisted in the fact that one organic compound can be related to several diseases, and so, scientists have not been able to link the discovery of one organic compound in a person’s breath with a specific diagnose. Haick’s experiments are different, because he is looking for patterns in the distribution of the volatile compounds. According to his theory, each disease
produces its own combination of organic compounds, so if he can prove a disease’s special “smell print” in the breath, the person probably suffers from the disease.
A total of 1,404 people from five different countries have contributed their breath to Haick’s studies, and the results are very promising. Based on nothing but breath, the electronic nose can diagnose the disease with a success rate of up to 86 %. So far, Haick has identified the breath marks of 17 different diseases, and now, the challenge consists in mapping out the special smell patterns of more diseases and recording them in a database. The aim is to enable ordinary doctors to use the quick and painless method to determine what is wrong with their patients.
Mice smell brain injury in urine
At the Monell Chemical Senses Center in Philadelphia, scientists are studying whether smells can also reveal how physical injuries affect the body. Based on mouse experiments, they have concluded that the make-up of the body’s breakdown products changes, when the mouse’s brain is subjected to external influence. And other mice can learn to identify peers with concussions only by smelling their urine.
Scientists do not yet know the exact substances that cause the smell of concussion. The substances could come from the immune system or be produced by intestinal bacteria. If scientists find out which substances the smell consists of, how long after the blow to the head it occurs, and how long it lasts, it could be an important new diagnosis tool for doctors. Concussion does not always cause evident symptoms, and so there is a risk that it is not identified in time. With diagnoses based on smell, doctors can quickly determine if a person had a concussion in a sports or traffic accident and monitor whether the treatment works.
Doctors smelt faeces
Electronic noses are not part of doctors' medicine bags yet, but the idea of detecting disease by its smell is not a new one. Around 2000 BC, Chinese doctors smelt tuberculosis, and in Ancient Greece, doctors smelt the faeces and urine of royal babies every day to rate their health.
During both world wars, infections in soldiers were a major problem, and wounds infected by the Clostridium perfringens bacterium typically developed into gangrene. Back then, there were no other ways to detect the bacterium, so doctors taught themselves to identify it based on smell. Today, some trained nurses can recognize the type of diarrhoea that is caused by the Clostridium difficile bacterium only based on the smell of the faeces. But it does not necessarily require medical training to smell disease. Experiments have shown that we apparently all have the ability to smell disease already in its early stages.
At the Karolinska Institutet in Sweden, neurologist Mats Olsson has tested what happens to body odour, when the immune system is activated by disease. Four in eight healthy test subjects were injected with LPS, which causes a severe, but harmless immune reaction, whereas the other four were injected with salt water. Four hours later, the participants’ T-shirts were collected, and 40 other test subjects were asked to describe their smell. The "verdict" was unambigous: The people whose immune systems had been activated secreted a sweat that smelt worse or more “unhealthy” and much more heftily than the control group’s sweat.
According to Mats Olsson, the ability to identify immune reactions in others might have meant something to human survival. The experiment shows that the human nose is able to detect disease long before the patient has visible symptoms, and the ability probably allowed us to avoid contact with sick peers.
Several other experiments have shown that our sense of smell is not as bad compared to that of other species, as scientists used to believe. Measured by the number of smell receptors in the nose, it is not impressive, but on the other hand, the part of the brain that analyses and interprets the olfactory perception has turned out to be much more complex than in animals.
In connection with some smells, humans are even better than animals at identifying the molecular signals. That may be due to our smell receptors being particularly sensitive to smells that are relevant to our species.
Joy Milne’s nose predicts disease
Eight months after the experiment, in which Joy Milne of the UK smelt T-shirts from Parkinson’s patients and compared them with healthy people, scientists received sad, but scientifically interesting news: One of the people of the control group had been diagnosed with Parkinson’s.
Joy Milne identified all six Parkinson’s patients based on the smell of their T-shirts, but apparently made one mistake: She diagnosed one of the people in the control group to be a Parkinson’s patient, and now she had been proved right. To scientists, this emphasizes the immense potential of smell as a diagnostic tool.