Study says the animals appear able to identify people infected with the disease even if they are not showing symptoms

Dogs’ noses could become a powerful weapon in the battle against malaria, according to research suggesting the animals can tell from a sniff of a sock whether someone has the disease.

Dogs have previously proved highly accurate at detecting a range of human diseases, including prostate cancer and thyroid cancer, as well as at alerting people with diabetes that they have low blood sugar.

Now experts say dogs also appear able to identify individuals infected with malaria, even if they are not showing symptoms.

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“Many countries are getting near elimination or have achieved elimination [of malaria] – for example, recently Sri Lanka became malaria-free, which is an extraordinary achievement,” said Steven Lindsay, a public health entomologist at Durham University who led the research. “The question then is how do you keep the place malaria-free, because the mosquitoes aren’t going away.”

The problem, he says, is that while some people fall sick very quickly from malaria, others can carry the parasites without any obvious symptoms. “If you have one in 1,000 people with a malaria parasite, you can’t finger-prick and take blood from 1,000 people to identity that one – you need a non-invasive [approach],” he said.

The answer, he says, might lie in the canine nose.

“Individuals that are infected with malaria parasites produce odours in their breath and from their skin that are specific signals,” said Lindsay.

The research, presented at the annual meeting of the American Society of Tropical Medicine and Hygiene in New Orleans and funded by the Bill and Melinda Gates Foundation, involved asking schoolchildren in the Gambia to wear nylon socks overnight and give a blood sample that was screened for signs of malaria.

The socks were then frozen and packed off to the UK where two dogs – a Labrador and a Labrador-retriever cross – were taught over several months whether the socks had been worn by children with malaria or not.

Socks from 30 from malaria-infected children and 145 uninfected children were used. Crucially, the team note, socks were only used from those with the disease if the child did not have symptoms.

The dogs were then put through their paces by being presented with a small group of the socks at a time, with each sock individually contained within a glass jar. The team watched to see whether the dogs would pause at any of the socks – the sign they had been taught to perform if the sock had been worn by someone with malaria.

The results reveal that each dog correctly identified the socks of children with malaria about 70% of the time and correctly recognised socks worn by uninfected children about 90% of the time.

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Lindsay said both dogs struggled to spot malaria-infected socks from children for whom the malaria parasites were not reproducing asexually inside the body. Instead the parasites had reached a different stage in their reproductive cycle, giving rise to cells that, once inside a mosquito, would develop into male and female sex cells.

“It might be that the odours produced by the parasites change if you are at the sexual stage or asexual stage,” said Lindsay, adding that the false positives may have been down to uninfected children sharing a bed with a child with malaria.

Lindsay said it was unlikely that the dogs were simply remembering which socks were which. “That is unlikely because they weren’t able to identify the sexual parasites – that says to me that they actually know the parasites rather than the person,” he said.

Lindsay stressed that the study was a proof of principle and more needed to be done, including testing the approach with real people rather than socks, and in different regions where there are different strains of malaria parasite.