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In November 2016, a team of scientists from the Medical Research Council in The Gambia visited primary schools equipped with hundreds of beige nylon socks. The researchers distributed them to children aged 5 to 14, aged 5 to 14, asking them to wear the socks during the night and to remove them only if they wash their feet for prayer. The next day, they came back for the dirty laundry, sorting it and mailing it to a British charity that would spend the next four months using the equipment to train dogs to recognize an imperceptible smell for the human nose: the molecular signature. malaria.
Dogs have a much more sensitive sense of smell than even the most advanced synthetic instruments. What is the power of a puppy schnoz? Powerful enough to detect substances at concentrations of one third per trillion – a single drop of liquid in 20 Olympic-sized pools. With a workout, the dogs can detect the bombs and the drugs, pursue the suspects and find the corpses. And more and more, they are used experimentally to detect a human disease – cancer, diabetes, tuberculosis and now malaria – from the sense of smell alone.
On Monday, researchers presented these latest results at the annual meeting of the American Society of Tropical Medicine and Hygiene in New Orleans. In double-blind laboratory tests, two dogs were able to correctly detect the scent of children infected with malaria parasites in 70% of cases. Although all schoolchildren appeared to be in good health, on-site blood tests revealed that 30 children were actually carriers of the disease. This work is only a proof of concept, but the hope is that one day, biosensing dogs could be deployed at airports, entry points or other border crossing points, to prevent Asymptomatic carriers of the malaria parasite bring it back to areas where the disease has been eradicated.
The work was funded by a grant of $ 100,000 from the Bill & Melinda Gates Foundation, which has made malaria a priority in recent years, even leading an ambitious effort to eradicate the disease through mosquitoes published by Crispr. In its latest report on malaria, the World Health Organization warned that advances in the fight against the disease for decades have been stalled and are likely to reverse. Each year, it kills half a million people, mostly children.
"The next step is to determine how far dogs can behave in natural conditions with real people," said James Logan, head of the Department of Disease Control at the London School of Hygiene & Tropical Medicine, who collaborated in the research. If they prove to be quite skilled, dogs could become a routine non-invasive screening tool. They may be particularly useful during dry months, when there are few mosquitoes and very little transmission of the disease, but the parasite is hidden in human hosts that show no symptoms. "It's very hard to find these people right now," says Logan.
In this study, dogs were trained to detect malaria through the odor of the disease in sock samples worn by infected children.
Medical detection dogs
An entomologist by training, Logan spent the early years of his career trying to understand why some people are more attractive to mosquitoes than others. A few years ago, he began to wonder if, like other parasites that depend on multiple hosts to carry out their life cycle, cause malaria. Plasmodium had a way to make infected humans smell more tasty for winged blood suckers. Through a series of experiments, his research group showed that, in fact, people infected by the parasite emitted a unique aroma that warmed the skeeters. They have identified a cocktail of volatile compounds that has proven effective in attracting mosquitoes.
The origin of this molecular beacon is still a mystery. Logan offers three possibilities: the parasite can produce it, the stress due to the presence of a parasite in the body can induce human cells to secrete it, or the infection modifies the bacterial communities living on the skin, thus producing the perfume feature. The next phase of their research is trying to better understand the details, so that they can one day develop a device that does the job of a dog's nose, without the need for an ecopist. And in the meantime, they plan to start real-world trials to see how dogs behave with people, not just socks.
So, how do you train a dog to detect diseases? In the same way, you train one to release a puff of gunpowder or heroin. You start by teaching them a sniff game.
"Dogs have a phenomenon called neophilia, which means that they are attracted by new, interesting smells," says Claire Guest, head of Medical Detection Dogs, a charity founded ten years ago and dedicated to supporting research on canine biodetection. At their London location, trainers put a few drops of standard training fluid in small glass jars. These cut behind a metal grid attached to a vertical arm, aligned next to each other. The dogs are instructed to go down the line, stopping to sniff them. If they stop at the new smell, the coaches believe, "That's it, good dog." Soon, they will learn that they stop and sit in showing the good pot, they will have a sweet.
Dogs do not live in the facilities. They live with families in the area and come every day for a few hours of work. It may take a few weeks to learn the basics of the game. But once that's done, you can get them to other smells, like schoolboy socks. MDD has trained three dogs to detect malaria; a spaniel named Freya, Sally, a Labrador and Lexi, a Lab-Golden Retriever mix. These are 3 of the 38 dogs currently working for the organization. Others learn to detect prostate cancer, colorectal cancer, diabetes, Parkinson's disease and, in the most recent trials, the bacteria that causes urinary tract infections. Each dog is trained only in one disease indication, but not because he can not learn more than one. Their human manipulators just did not know who was who. In theory, you teach them to lift the right paw against malaria and the left paw against diabetes, but that would probably introduce more errors into the equation.
All this work is deeply personal to Guest, whose father died of Parkinson's a few years ago. In 2009, his own dog, Daisy, gave him several nudges in the chest, causing him to drop a mass that turned out to be breast cancer. But she is particularly excited about some of the organization's more external research. MDD is collaborating with a scientist in Mexico City who has built a bioelectronic nose to detect cancer by smell. But his algorithms must learn to smell the smell of the malignant tissues. That's where the dogs come in. "We can tell the dog," Here are 10 cancers, that smells the loudest, "and then we pass that data to the AI," says Guest. "If machines can understand what an odor is, it will be a much more powerful tool for us in the future."
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