Sock Sniffers: How Dogs Can Help Eliminate Malaria

Almost every day it seems that dogs serve new heroic purposes beyond being “man’s best friend.” They’ve long been relied on as guides for the visually impaired, pillars of emotional support, and some of the first on the scene when disaster strikes. Now another role is being added to the list: disease detection.

Dogs today are detecting various types of cancer by using their sense of smell, and now a new report outlines how scientists have started to enlist dogs’ superb olfactory senses to detect malaria. At the 2018 American Society of Tropical Medicine & Hygiene (ASTHM) annual meeting in New Orleans, investigators presented research on how dogs can detect the distinctive odor that is emitted by malaria parasites. The success rates from initial tests have led scientists to believe there is potential for dogs to assist in malaria eradication campaigns, which have stalled in many parts of the world.

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In a recent proof-of-concept study, trained dogs correctly diagnosed malaria infections simply by sniffing samples from socks worn briefly by children from a malaria-endemic area of West Africa. The research was conducted jointly by investigators from the London School of Hygiene & Tropical Medicine and the charity Medical Detection Dogs, which is well versed on training dogs to detect a variety of maladies, including prostate cancer and insulin abnormalities.

People with malaria have distinct odors on their skin. “Our study found dogs, which have an incredibly sensitive sense of smell, can be trained to detect these odors even when it’s just on an article of clothing worn by an infected person,” said Steven Lindsay, PhD, a public health entomologist at Durham University in the United Kingdom and the lead author of the study.

Detecting Malaria Via Sock Samples

The experiment originated at the London School of Hygiene & Tropical Medicine, where several hundred school-age children were checked for overall general health, sampled for malaria parasites, and then provided with a pair of socks to wear overnight. The following day, the socks were collected and sorted according to the malaria infection status of the children who had worn them. Socks were collected from children with malaria but no fever as well as from uninfected children; samples were then frozen.

The dogs were then trained to sniff each sample as they walked past it. They were to freeze if they thought they detected malaria or continue walking if they did not. Using only the sock samples, the dogs correctly identified 70% of infected children and 90% of uninfected children. What impressed the investigators most was that the dogs were able to identify malaria-infected children who had lower levels of parasites than required to meet clinical standards for rapid diagnostic tests set by the World Health Organization.

Dr. Lindsay and his colleagues are confident that the success rate might have reached 78% had all of the children with malaria been carrying the same type of parasite. This is because as malaria infections progress, the parasite goes through several stages of development; when it reaches maturity, the odor it generates on human skin is altered. Further testing of the children revealed that some were carriers of these mature parasites, but the dogs were not trained to detect the associated odor. The group also believes the success rate might have been higher if the dogs were actually with the children or working with socks that had been worn recently instead of frozen samples.

Looking Ahead

Although this study was devised only to establish proof of concept, the group is considering a follow-up study that would test samples from people in different parts of Africa to test whether there are geographic differences in the odors the parasites emit. The investigators believe that with additional training and more samples the dogs could end up with an accuracy rating that rivals a clinical test.

Dr. Lindsay said trained dogs could be vital to a malaria elimination campaign that requires treating anyone in a village or community who is still carrying malaria parasites, including those with no presenting symptoms. Currently, the only way to address the problem of asymptomatic carriers—who still can cause new infections—is to test or treat an entire community.

“With this innovative approach, these researchers show that new tools to tackle malaria can come from unexpected places,” said ASTHM President Regina Rabinovich, MD. “Funding to support these innovations is critical to achieving the global goal of eliminating, and eventually eradicating, malaria from its remaining strongholds.”