A new leash on infections: dog that sniffs out a deadly superbug

December 18th, 2012
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Beagles are known as good hunters. So why not send them in search of deadly bacteria?

That’s what Dutch doctors are hoping to do by training the dogs’ famously sensitive sense of smell to sniff out deadly pathogens that plague hospitals and put patients at risk.

Doctors spent two months training a two-year-old beagle named Cliff to learn to lie down or sit whenever he smelled the presence of Clostridium difficile, stubborn bacteria that cause severe, hard-to-treat diarrhea and sometimes life-threatening colitis. Cases of C. difficile have reached historical highs in recent years, claiming 14,000 lives in the U.S. each year, primarily in hospital or long-term care settings. Reporting in the BMJ, the researchers say the hound accurately detected C. diff in nearly all of 50 stool samples, and accurately did not respond to another 50 samples that were negative for the bacteria.

That success justified testing Cliff’s sense of smell around patients in a hospital, and indeed he correctly identified 25 of 30 people who were sick with the infection, and also identified 265 of 270 who were not sick – a remarkable rate of accuracy for a diagnostic tool that’s almost instantaneous and completely non-invasive. It’s also encouraging since Cliff was trained to detect even the slightest presence of C. difficile, wafting in the air from a wooden stick, piece of fabric or plastic vial carrying the bacteria.

“It would be very interesting to see whether you can use a dog like Cliff to actually reduce C. difficile incidence,” says lead study author Marije Bomers in an email to TIME. Bomers, an internal medicine doctor at VU University Medical Center in Amsterdam, says that dogs could potentially conduct a “pet scan” of hospitals or healthcare facilities where C. difficile is a particular problem. Early detection, she hopes, could lead to stricter hygiene and containment strategies that could ultimately lead to reduced transmission. “The idea holds great potential,” Bomers says, “but more research has to be done first to see whether this concept actually works.”

There’s good precedent for exploiting canines’ refined sense of smell: dogs routinely sniff out explosives and other chemicals used to make bombs, and they have even been tested as a potential cancer screener, to pick out the scent of lung and colon tumors in patients’ breath.

Needless to say, Cliff isn’t the only option for sussing out C. difficile. Assays that detect the bacteria are pretty reliable, but require culturing cells that nurture the pathogen, which can take one to two days. by that time, patients may have passed on the infection to others. And while newer and quicker enzymes tests can also pick out the bug, those screens are more expensive and require specialized equipment that not many hospitals or public health facilities would have.

The recent rise in C. difficile infections is concerning because most occur among frail and immune-suppressed patients who are receiving care in close quarters, such as hospital wards or nursing homes, where infections can spread quickly. Most have received antibiotics, which may make them more susceptible to C. difficile since the drugs can also kill off some of the healthy bacteria that reside in a person’s gut, allowing C. difficile to run rampant. Treatment is not always effective and, ironically, usually requires more antibiotics.

Bringing in dogs for rapid detection was an idea born after Bomers and colleagues heard a nurse remark on the distinctive smell of diarrhea coming from patients with C. difficile.

“We thought, ‘Hey, if a human nose can recognize C. difficile with reasonable accuracy, a dog should be able to do it easily, since they have such an amazing sense of smell,” Bomer says. It’s not clear whether Cliff is smelling the bacteria itself in high concentrations, or the toxins that the bacteria produce. Either way, Bomer’s study shows that Cliff is smelling the pathogen with admirable accuracy.

So far, in fact, there’s only one barrier in bringing in sniffer dogs to detect C. difficile. Not every patient loves having a dog around – while some may love it too much. For their research study, Bomers and colleagues tried to bring Cliff in to do his work in a pediatrics ward. But alas, the researchers write in their journal article, the kids soon “became excitable by having an animal on the ward” and they “distracted the dog,” who couldn’t perform his duties. Even dogs, it seems, will use any excuse to put off work.

~ Courtesy of Time

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