Yellow fever smells like a butcher’s shop while TB apparently has the odour of stale brown bread.
Centuries ago doctors used scent to detect illness and now scientists believe the age-old tradition could be a powerful weapon in the fight against malaria.
In an unlikely study, dogs have been shown to be able to sniff out the disease from used socks of school children.
Scientists believe it could stop the spread between countries and lead to infected people being spotted and treated earlier.
Head of the disease control department at the London School of Hygiene & Tropical Medicine (LSHTM), Professor James Logan, said: ‘Worryingly, our progress on the control of malaria has stalled in recent years, so we desperately need innovative new tools.
‘Our results show that sniffer dogs could be a serious way of making a quick diagnosis of people who don’t show any symptoms but are still infectious.’
Dogs have previously proved highly accurate at sniffing out various cancers, Parkinson’s disease as well as alerting people that their blood sugar is low.
Professor Logan suspected they could also be trained to smell malaria – a condition that still claims over 400,000 lives each year.
In the study, seemingly healthy children in the Gambia were given nylon socks to wear overnight.
They were also given a blood test to see if they had the malaria parasite after being bitten by an infected mosquito.
The sock samples were then frozen and transported to the Medical Detection Dogs (MDD) charity in Milton Keynes, Bucks.
Two dogs, a Labrador-Golden Retriever cross called Lexi and a Labrador called Sally, were trained to distinguish between the scent of children infected with malaria parasites and those uninfected.
They were presented with socks in a glass jar and able to correctly identify 80% of the samples, which is above the World Health Organisation (WHO) threshold for successful diagnostic tests.
Scientists said the true accuracy is probably higher as children may have swapped socks or shared a bed, which confused the results.
Biotechnician at Medical Detection Dogs, Mark Doggett, told Metro.co.uk: ‘A person has five million scent receptors in their nose. A dog has 300 million.
‘Their sense of smell is so much better than ours and the scheme was all about harnessing what nature has given them.’
Last year, WHO recorded 228 million malaria cases worldwide.
Worryingly, the malarial parasites are becoming resistant to treatment and there are fears climate change could make the situation worse.
Malaria mosquitoes prefer to feed on people already carrying the parasite and scientists believe they are attracted by an odour.
Some people will fall sick with the condition – characterised by fever, vomiting and weakness – but others can carry the parasites without any obvious symptoms.
Countries and communities that have eliminated malaria are at risk of new infections because of these asymptomatic carriers.
Professor Logan explained that trained dogs could be placed at ports and borders as a non-invasive way of screening travellers.
Those with the parasite could be treated with anti-malarial drugs and the spread of the disease can be prevented.
The work was led by LSHTM, MDD and Durham University and funded by a $100,000 (£80,000) grant from the Bill & Melinda Gates Foundation.
The team is currently fundraising for a second phase, which would see dogs taken to southern Africa to see if they can replicate the results in the field.
Some of Lexi and Sally’s canine colleagues are now also being trained how to sniff out malaria.
Mr Doggett said: ‘I’m confident the dogs will be able to do it on a larger scale. I’m confident the principle works. My hope is we have dogs deployed around the world being able to screen people as part of the fight to eradicate malaria.’
And what does malaria smell like? According to Professor Logan ‘slightly fruity.’
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