Dogs can pick up odors that develop on human skin due to malaria parasites.
In the United States, doctors diagnose about 1,500 cases of malaria each year, according to the Centers for Disease Control and Prevention (CDC).
Although the number of infections is relatively small, a delay in diagnosis is the primary cause of death among people with malaria in the U.S. Currently, a person's physical symptoms determine diagnosis, but, ideally, the CDC recommend that laboratory tests — such as microscopic analyses of blood smears — should confirm the symptoms.
New research, however, shows that dogs can diagnose the infection quickly, accurately, and in a noninvasive way. Steven Lindsay, a public health entomologist at the Department of Biosciences at Durham University in the United Kingdom, is the lead investigator of the new study.
Lindsay summarized the findings at the American Society of Tropical Medicine and Hygiene (ASTMH) Annual Meeting, which this year took place in New Orleans, LA.
"People with malaria parasites generate distinct odors on their skin, and 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."
Dogs sniff out 70 percent of malaria cases
As the study's lead author explains, the research began in The Gambia, where specialists tested hundreds of school children for malaria parasites and gave them a pair of socks to wear overnight.
The researchers collected the socks the next day, sorted them according to the children's status of malaria infection, and stored them in a freezer for several months. Lindsay and colleagues only collected socks from children who had malaria but did not develop fever, as well as children who did not have the parasite.
In the meantime, experts at the Medical Detection Dogs charity trained dogs to freeze if they detected malaria, or move on if they did not. In this experiment, using the sock alone, the dogs accurately identified 70 percent of the malaria infections and 90 percent of the children who did not have the disease.
The researchers report that the levels of parasites identified by the dogs were lower than those required by existing "rapid diagnostic tests," which offer a diagnosis in 2–15 minutes.
Also, Lindsay says that the diagnostic accuracy rate might have been even higher if the children were all carrying parasites that were in a similar stage of development.
The researcher explains that as the infection advances, the parasite goes through different stages, and when it reaches a level of maturity, its odor on the human skin might change. The dogs were not trained to detect these mature parasites.
Finally, the researchers think that the accuracy rate would have also been higher if the dogs had access to more recently worn socks, rather than frozen socks.
A quick and easy way to diagnose malaria
The researchers comment on the significance of their "proof-of-concept" study. They point out the urgent need for new diagnostic tools, as the global number of malaria cases and deaths has been rising over the past 2 years.
"Worryingly, our progress on the control of malaria has stalled in recent years, so we desperately need innovative new tools to help in the fight against malaria," says Prof. James Logan, head of the Department of Disease Control at the London School of Hygiene & Tropical Medicine and a co-author on the study.
"Our results show that sniffer dogs could be a serious way of making [a] diagnosis of people who don't show any symptoms, but are still infectious, quicker, and easier."
Prof. James Logan
"With this innovative approach, these researchers show that new tools to tackle malaria can come from unexpected places," says Dr. Regina Rabinovich, the president of the ASTMH.
"Funding to support these innovations is critical to achieving the global goal of eliminating — and eventually eradicating — malaria from its remaining strongholds," adds Dr. Rabinovich.