27 May 2018

Smelling disease

In the world of medicine, smell is an underutilized sense.   Experienced clinicians can learn to detect the odor of ketones on the breath of a diabetic in ketoacidosis (and presumably this is the basis for using sentinel dogs to alert their diabetic owners to check their status).  Dogs have been reported also to identify impending hypoglycemia by detecting isoprene.

From a BBC science podcast this week I learned that researchers have found that malaria can be detected by smell.  It has been known that mosquitoes can locate malaria carriers and will bite them more often than unaffected people - an ability presumed to be mediated by their sense of smell.  A team of researchers tested this by giving children in a malaria-endemic area socks to wear, to absorb their sweat and body odor.  They found that socks from children carrying the malaria parasite smelled different from those worn by normal children, that mosquitoes favored those socks, and most importantly that when they treated the children for malaria, their sock smell reverted back to normal.  One implication of this is that it might be possible to detect subclinical malaria noninvasively, without requiring phlebotomy and a microscope.  I found some discussion of the research at NPR.

Less intuitive is the reported ability of some humans to detect Parkinson's disease by smell.
... Joy Milne from Perth, whose husband Les was told he had Parkinson's at the age of 45. About a decade before her consultant anaesthetist husband was diagnosed, Joy noticed she could detect an unusual musky smell... Joy said: "We had a very tumultuous period, when he was about 34 or 35, where I kept saying to him, 'you've not showered. You've not brushed your teeth properly'.

"It was a new smell - I didn't know what it was. I kept on saying to him, and he became quite upset about it. So I just had to be quiet." The retired nurse only linked the odour to the disease after meeting people with the same distinctive smell at a Parkinson's UK support group.

She told scientists at a conference, and subsequent tests carried out by Edinburgh University's Dr Tilo Kunath confirmed her ability...

Joy was given 12 unmarked T-shirts to smell - six worn by Parkinson's patients and six worn by volunteers without the disease. She correctly identified the six worn by Parkinson's patients, but could also smell the odour on a T-shirt worn by someone in the control group without Parkinson's. Joy was told three months later that this person had in fact been diagnosed with Parkinson's after the T-shirt tests.
No time to search today.  I bet there are a lot more things that could be added to this post.


  1. 'Normal children' as opposed to 'affected children'.

  2. smelling is used in traditional chinese medicine to determine diseases.


  3. I hope diabetic alert dogs are not relying on the smell of ketoacidosis - this is a medical crises which occurs when the level of glucose in the blood is so high it causes the blood to become acidic and begin disolving muscle tissue. This requires hospitalization and can be fatal. An alert dog would hopefully detect high blood sugar at much lower levels.
    The dogs may be smelling the sugar itself - the word "diabetes" comes from the characteristic sweet-smelling urine, it wouldn't surprise me if sweat or breathe also gained a noticeable sweet smell, at least to the nose of a dog.

    1. They are relying on the scent of ketone bodies (mostly acetone- literally nail polish remover) which gradually rise in concentration in the blood causing bad breath and other symptoms along the way. One would anticipate that the dogs could detect the ketone bodies well before they rose to the level that causes, as you say, the very dangerous state of ketoacidosis.

      As a side note the rise in Ketone bodies and associated bad breath and body odor is also commonly associated with extreme low-carbohydrate diets such as the Atkins Diet.

  4. The mosquito bit is a little counter-intuitive because the malaria parasite also parasitizes the mosquito. Why would it feed more often on hosts that would cause it to become infected?

    The NPR article contains the answer. The parasite manipulates the human's body chemistry to cause them to generate more aldehydes which are a normal human scent that mosquitoes regularly use to find victims.


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