You’ve probably heard about domestic dogs that are trained to sniff out drugs, explosives, and bad guys.
You may also know that canines can detect the tiny molecular changes that distinguish cancer cells from healthy ones. Dogs in studies have perceived lung and breast cancer via a whiff of a patient’s breath, ovarian cancer from smelling blood, melanoma from the scent of skin, and colorectal cancer from the stink of stool samples. (Explore a human-body interactive.)On August 1, 2013, Jonathan Ball (right) introduces Marta Drexler, an ovarian cancer patient, to McBaine, who is participating in a study about how dogs detect cancer. Photograph by Matt Rourke, AP
But enough about canines; they aren’t the only creatures with olfactory systems many times more sensitive than ours that we can tap for help.
This list is ever growing, but here’s a quick look at some unexpected “sniffers” that can perceive scents undetectable by humans—such as the VOCs (volatile organic compounds) associated with diseases—and then share their findings with us.
In brand-new work published online in Scientific Reports, scientists reveal that fruit flies—those tiny, pesky buggers that dive bomb your fruit bowl but also contribute vastly to the world of lab science—have quite a penetrating sniffer that can be used to detect cancer cells.
The insects’ antennae are covered in receptor neurons that let them recognize very low concentrations of medically relevant odors. What’s good about flies versus dogs as sniffers is that their response is physiological (a boost in calcium within the cells), not behavioral, and can be observed right there on the antennae surface. (The scientists use a technique called calcium imaging, which employs a fluorescing sensor that lights up calcium as it increases.)
Also unlike dogs, flies’ “answers” to questions (i.e., “is there breast cancer here?”) aren’t affected in any way by the handler, which is one critique of some sniffer-dog techniques. Study co-author Giovanni Galizia of the University of Konstanz in Germany said that flies could become the gold standard when it comes to assessing sniffers of the future.
Giant African Pouched Rat
Tuberculosis kills… especially in sub-Saharan Africa where, in 2012, there were more than 255 cases of this bacterial disease per 100,000 people, according to the World Health Organization. And one of the tools used to detect this disease? The giant African pouched rat.
Maybe it’s not so surprising; if you’ve ever watched a rat of any sort skittering around in the bushes or a back alley, you’ll note that its whiskered nose vibrates nonstop. But these super-size, big-cheeked rodents in Tanzania are following their noses to save human lives.
While the smear biopsy (looking at a patient’s spit under a microscope) is still the most widely used TB detection method in Africa, it isn’t very precise and the diseased cells are easy to miss.
The rat, on the other hand, can smell the difference between TB and other germs in human saliva more than 86 percent of the time, according to studies. And the animal picks up around 44 percent more cases than does the microscope. The same species has been used to smell for landmines in war-torn countries.
We humans aren’t the only animals that suffer from disease, and detecting illness in our creature cousins can be vital to industries such as beekeeping and farming.
Scientists at the Monell Chemical Senses Center in Philadelphia found that mice react strongly to a disease-related chemical, or more likely a suite of chemicals, in the poop of birds (in this case, ducks) with avian flu.
Most likely the smelly bit isn’t actually the stink of the flu, but is instead released by the duck as part of its immune response, the scientists wrote of their finding.
Regardless, the research showed that mice have highly perceptive snouts and can be trained to find markers of avian or other diseases—leading to an earlier response to outbreaks, and with that a reduced chance of the disease spreading to humans.
You are still more likely to see dogs making rounds at the airport, but in some terminals honeybees have invaded security checkpoints. (Related: “Detection Dogs: Learning to Pass the Sniff Test.”)
Like flies, honeybees have incredibly sensitive antennae, and they are surprisingly quick and easy to train if you reward them with enough sugar water.
Developers from a company called Inscentinel have come up with a handheld device, resembling a hand vacuum cleaner, that holds 36 bees gently within cells while they work; the “vacuum” draws air over the bees from a sample (a bag, for example), and the insects are trained to extend a proboscis at a particular smell, a movement that sends information to a screen on the detector.
The user can immediately see how many bees respond positively, indicating, say, the scent of an explosive. If enough bees vote “yes,” it’s time to pull a passenger aside. Bees probably won’t replace dogs at airports anytime soon, but they’re another potential tool in the crime-fighting kit.
Called electronic noses or gas sensor arrays, these chemical analyzers are being used more and more to look for markers of cancer in cell cultures and in breath. But scientists and developers aren’t satisfied yet with the existing products and continue their research to improve the design and sensitivity, trying to make the electronic noses more precise than animals (a tough goal; dogs can tease out scents present in parts per trillion).
Said fruit fly researcher Galizia, “Natural receptors are still far superior to e-noses. I would guess the most promising path for quite a while will be to learn from the animal world and even build hybrid systems” that use both electronics and nature. (Read about robots in National Geographic magazine.)
Meanwhile, work like his team’s on the fly could propel us toward a more sensitive electronics-only olfactory machine—a tool that wouldn’t beg for sugary treats or belly rubs.
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