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Dog-sized rats sniff out TB in patients

Chris Tachibana writes: Could a giant, spit-sniffing rat save your life? Maybe — they can be better than humans at diagnosing tuberculosis.

A pilot program in Tanzania is using trained rats to smell TB in sputum samples. Up to 1,000 samples a week are collected from local hospitals by APOPO, a nonprofit that also trains rats to sniff out landmines. Although the TB samples have already been checked by a human under the microscope, the rat pack’s sniff tests have improved disease detection by 44 percent because the clever rodents often find TB that was missed.

While the World Health Organization estimates that 2 billion people around the world are infected with TB, it can be hard to detect under a microscope, particularly in those who are also HIV positive. That’s where the giant rats can help. They might turn out to be just as accurate at finding TB. They're low-tech and could screen for TB in resource-limited countries. They’re also faster than the standard microscope test, says Bart Weetjens, APOPO founder. A human with a microscope can process 40 samples a day. A rat can do 40 in seven minutes, he says.

Weetjens, who was inspired by a childhood pet rat, started APOPO in the 1990s to train giant pouched rats, which are native to sub-Saharan Africa, to detect land mines in the region. The rats were so good at sniffing out hidden bombs that in 2003, APOPO started training their nosy little friends to smell TB in a spit sample. Currently working with a team of 30 rats, APOPO is now optimizing their unique program, so in the future, it might be used in other communities.

Rats aren’t the only creatures making medical diagnoses. Dogs can also be trained to find disease in humans, like smelling urine samples for signs of cancer. (One little terrier recently chewed off his owner’s big toe after sniffing out a dangerous diabetes-related infection.)

But in a nose-to-nose contest, Weetjens says rats are better than bomb- or disease-sniffing dogs.

"Whatever dogs can detect, rats can detect equally well," he says, noting a rat can be trained for one-fifth the cost. "They're more calm than most small animals, very intelligent and social, and they love humans."

Rats’ reputation as disease-carrying vermin is exaggerated. Weetjens says that in 12 years of working with the giant rats, no one at APOPO has gotten sick from them. The rats themselves are resistant to TB and many tropical diseases. "They're really lovable creatures," says Weetjens. "Like a pet you can work with."