Malaria kills hundreds of thousands of people every year, but the parasite itself, Plasmodium falciparum infects many more people than…
Malaria kills hundreds of thousands of people every year, but the parasite itself, Plasmodium falciparum infects many more people than it gets sick. The majority of people with malaria are at all times healthy, goats and parasites, and without knowing they are infected, these healthy carriers can easily spread the disease to new regions and new people who may not be so lucky.
Fortunately, man’s best friend is here to lend a helping hand to a doctor.
New research from the London School of Hygiene & Tropical Medicine suggests that dogs can identify the smell of malaria. In a small study with evidence of concept, two trained dogs could distinguish between socks bore of children who had malaria and socks from the feet to those who did not. Researchers presented their preliminary results today at the American Society of Tropical Medicine and Hygiene Annual Meeting.
Malaria is known to make people more attractive to mosquitoes. A team led by James Logan, director of the Department of Disease Control at London’s Tropical Medicine School, showed earlier that socks carried by infected children were more appealing to the small blood suckers, probably because of the smell of the plague containing more chemicals called aldehydes. With small threads connected to the antennas of the mosquito, scientists poked chemicals on them to see what odor gave rise to a reaction. Compounds called heptanal, octanal and nonanal were the most exciting to the mosquitoes and found in higher levels in the infected children’s socks.
“So if mosquitos can [smell differences in people] why not dogs?” Says Steve Lindsay, a public health entomologist at Durham University in the UK and leading investigator of the new study.
The research group with medical discovery dogs.
(Durham University / Medical Detection Dogs / London School of Hygiene & Tropical Medicine)
Lindsay and colleagues apparently asked healthy kids in Gambia to wear a pair of new socks for one night. In the morning they collected the socks – about 175 pairs – and tested the children for malaria. (About 30 children were tested positive, even if they had no symptoms.) The researchers froze the socks to preserve the smells, unpack them and send them back to the UK
Nonprofit Medical Detection Dogs spent six months training two dogs called Sally and Lexi, to distinguish between socks worn by children with malaria and socks worn by children without the disease. The bags – a Labrador retriever and a Labrador mixed breed – would cut each sample and freeze if they discovered malaria, or continue if not. After training with a sock from each pair, dogs could properly identify 70 percent of the children with malaria and 90 percent of the healthy children by snoring the socks from the other foot. The dogs even picked infected children with very low parasitic loads – 10 to 20 parasites per microliter of blood. (The World Health Organization says that a malariaelectric tool should be 75 percent accurate at 200 parasites per microliter-but then again they did not specifically mention dogs.)
“I think it’s very exciting,” said Audrey Odom John, a pediatrician doctor researcher at the Washington University School of Medicine in St. Petersburg Louis. Odom John, who was not involved in the new study, developed a breath test to detect malaria agents in infected children. “It’s really a good start,” she says about the dog’s success.
However, there are some restrictions on the work. The sample size of 175 pairs of socks is less than medical detection dogs would have liked, says Claire Guest, founder and CEO of the idea. A better test would have been 100 malaria-positive socks and 300 negative socks, she says.
Due to the small sample size, the dogs must be trained on the same socks as they tested (the training was done with a sock from each pair and the test was performed with the other). The experiment is not ideal because the dogs could have learned to recognize individuals rather than detect the malaria agency.
However, Guest and her team consider that the dogs do not memorize individuals. When the dogs failed to identify a malaria-positive child, a child was often infected with the sexual phase of the malaria parasite, as Lindsay says may have changed the smell. If the dogs simply downloaded individual smells that matched one sock to the other, they should not have consistently made this mistake.
Overall, the team believes that the dogs did well, considering that they used “small pieces of socks used [once] by a child and then frozen for a while,” said Logan. “It gives us more hope that they could do much better if they could smell a real person because the signal would be much stronger. “
Smelling a person rather than a strump can also eliminate potential disturbing factors. Many of the children shared a bed with other relatives, for example, and the socks could have picked up odors from bedding or others. And “what little boys do with their socks, no one can say that,” says Lindsay. “We had a boy who appeared with a sock. What happened to the second sock? “
Lindsay says that the sniffer dogs may be helpful in ports where they come to countries that have eradicated malaria, but there are still Anopheles mosquitoes that spread the parasite. There are still healthy people who can carry the malaria parasite to prevent them from reinstating the disease to another “clean” country. As some estimates say that up to 19 in 20 people can carry the malaria parasite without getting sick, invasive means of identifying the wearers would be a great blessing for those who work to prevent the spread of the disease.
Current diagnostic methods are not practical to show hundreds or thousands of people passing an airport. To diagnose malaria, doctors can draw blood and use a microscope to identify the parasites, but it requires education and “things that work simple but not “like clean glass slices, a functioning microscope and reliable electricity,” says Heid in Hopkins, Malaria and Diagnostic Professor at the London School of Hygiene & Tropical Medicine.
Alternatively, healthcare professionals can use a number of “quick diagnostic tests”, which means that a blood clot is released on a small device. Fifteen minutes later, a colored bar appears if an antigen produced by the malaria parasite is present in the patient’s blood. Such tests are easy to use by non-professionals in any setting. The downside is that you can not force any international traveler to submit a blood sample. A dog, on the other hand, “could go down in a row of people and be done in a few seconds,” says Logan.
And if not sniffer dogs, maybe an electronic nose can be used. A device can be designed to detect the same compounds that dogs and mosquitoes smell – but to do that, more research on specific molecules is required.
An unknown part of the jigsaw is why exactly, malaria-infected people smell different. It is unclear whether the parasites produce odors directly, if they change a person’s microbiome, or if our bodies produce odors in response to the parasites. Odom John, however, says that the malaria parasite has a similar organism as one found on plants that produce odors – “what makes pines smell like pears or lemons smells of lemons.” It is possible that the malaria parasite produces odor substances directly with its strange organics.
Another avenue of research that needs to be investigated is whether the smell is consistent across the population, so Lindsay plans to test people from all over Africa to see if the dogs can recognize malaria among their scents.
One last complicating factor is that there is more than one type of malaria. P. falciparum is the most common and lethal, but other species of the parasite can cause diminishing recurrence months after the first infection.
Malaria is a complex disease that will not be easily eradicated, even with the help of our four-legged friends. But these pops – and their human trainer – will work with all their dogs can, in lab and field, make this underdog story a success.