By Jonathan Amos
BBC News Online science staff
Animals could soon be breath tested to diagnose their diseases, researchers from Glasgow University report.
Horses are being monitored for respiratory problems
Scientists have long understood that certain volatile chemicals in exhaled gases are linked to some illnesses.
The Scottish team tells the Veterinary Record journal it is well on the way to developing technologies to capture and test animal breath samples.
It says this would be done with a mask over the mouth which is less stressful than taking blood or a tissue biopsy.
"There is a spectrum of diseases we are looking at with this technology - respiratory disease, gastrointestinal problems, liver disease. It has massive potential," Dr Cathy Wyse, from the Institute of Comparative Medicine, told BBC News Online.
"There are about 3,000 compounds in breath and with many of them we have no idea where they originate from. But there is a good deal of evidence that many diseases have a unique signature in breath. We can look for patterns in the compounds."
In a chamber
For centuries, doctors dealing with human patients have known that certain odours on the breath are a good indicator of health problems - such as the pear drops smell on the exhaled air from a person with diabetes.
And the breath check is now creeping into human healthcare with a test to detect Helicobacter bacteria which can cause gastric ulcers.
But a great many other diseases, such as cancers, heart problems and even HIV infection, are being investigated with this approach.
What makes the tool so attractive in veterinary medicine is its ease of use. Large animals, such as dogs and horses, breathe into a mask and their sample is collected in a bag. Smaller or less cooperative animals, such as cats and rodents, can be placed in a chamber for the test.
"Breath samples can be collected anywhere and by people with no medical training," Dr Wyse explains. "The non-invasive nature of the breath test makes it a particularly attractive diagnostic method in veterinary medicine."
Dr Wyse and colleagues say the technologies for analysis - mass spectrometry, gas chromatography and various forms of biosensor - are rapidly becoming cheaper, more portable and easier to use.
They envisage equipment that will one day become so simple and portable that it could possibly fit into the boot of a vet's car.
The researchers tell the Veterinary Record about their latest work on dogs and horses which they believe will be among the first breath tests in clinical use.
The dog test examines the different types, or isotopes, of carbon atoms in the animal's breath after it has eaten a "labelled" substance in a meal. This can indicate whether the dog has disease of the digestive system.
"The test we're very excited about is one to look at respiratory problems in horses," said Dr Wyse. "A huge number of horses have a condition similar to asthma in humans and it is very difficult to monitor. At the moment, the only way we can do this is to take a sample of the horse's respiratory lining fluids. That's very, very invasive."
The researchers concede the routine use of such tests may be a few years away. They also have to work out the reference ranges for each particular component in the breath that will be used to distinguish between health and sickness in individuals of each animal species.
This involves testing a great range of diseased animals.
Dr Sergei Kharitonov, of Imperial College London, is using breath testing to investigate airway inflammation in humans.
He believes breath testing will become widespread in both human and animal healthcare.
"In asthma, nitric oxide is abnormally high, but in cystic fibrosis it is abnormally low," he said.
"If we are talking about signatures of disease, the best solution will be to measure several gases. You will measure four or five different markers and these will be different in different species."