Rat that sniffs out TB on HWN SPOTLIGHT

At a laboratory in southern Africa, Tariq correctly identified all six spit samples known to be positive for tuberculosis, the world's second most fatal infectious disease.

Tariq is no scientist, though. He's a lab rat—an African giant pouched rat, to be exact. Every weekday, the trained rodent and eight of his brethren take turns in a glass-sided cage at Eduardo Mondlane University's College of Veterinary Medicine.

Underneath the cage floor, a removable tray with ten samples of human mucus is inserted. Tariq walks the length of the cage, scratching the floor when he suspects that a sample is positive for tuberculosis, an airborne bacterial disease.

He works rapidly, taking only eight minutes to get through five trays containing a total of 50 samples. "Rats are very fast," said his trainer, Catia Souto, adding that one rat can evaluate more samples in ten minutes than a lab technician can evaluate in a day. (Related: "5 Animals With Spectacular Sniffers.")

Training rats to detect TB is a relatively new endeavor for APOPO, the Belgian nonprofit organization that's best known for using rats to find land mines. APOPO began using TB rats in Tanzania in 2008 and in Mozambique in 2013. Currently, the animals work in 21 medical centers in Dar es Salaam, Tanzania's capital, and double-check 75 percent of potential TB samples from medical centers in the Mozambique capital of Maputo.

Like the battle against land mines, the fight against TB—which claimed 480,000 lives in Africa in 2012, 58,000 of them in Mozambique, according to the World Health Organization—is badly in need of an innovative, rapid, and affordable detection technique. (Read "War on Disease—Challenges for Humanity.")

"We know that we need a new approach in the diagnosis of TB, so this could be one of the approaches," said Gaël Claquin, a TB/HIV specialist in Mozambique who is not directly involved in the APOPO project.

And so far, rats seem to be a promising solution: In the first 16 months of the Maputo program, the rats evaluated samples from roughly 12,500 patients. Of those, 1,700 had been found positive at the health clinics. The rats detected another 764 patients, an increase in detection rate of around 44 percent, according to APOPO.

Like many developing countries, Mozambique relies on a TB detection technique that's more than a century old.

Trained lab technicians use microscopes to look at mucus, or sputum, samples of potentially infected patients to see if TB bacteria are present.

The accuracy of the technique depends on the performance of the lab technicians and the state of the equipment.

In Mozambique, more than half the cases are missed, said Claquin, a former national program officer for TB at the World Health Organization (WHO) Mozambique. It's these cases that Tariq and his eight rodent buddies are tasked with finding.

Lab technicians can make mistakes, said APOPO rat trainer Lila Denis

"People can die because of that. So we check [the sample] again to see if it is positive or negative."

Trainer Onesia Nhampara rewards Maria for identifying TB in a mucus sample at APOPO's lab in Maputo, Mozambique.

After undergoing nine months of training in Morogoro, Tanzania, where APOPO is headquartered, the rats are put to work in the capital cities of Maputo or Dar es Salaam. In Maputo, Emilio Valverde, manager of the APOPO Mozambique TB Program, is in charge.

"What the rats are trained to do is associate the smell of TB with a reward, so it's what they call operative conditioning," Valverde said.

It is the same principle applied to detecting land mines, only the rats are trained to recognize the scent of specific molecules that reflect the presence of the tuberculosis germ—not the explosive vapor associated with land mines.

To keep the animals motivated, positive samples are mixed in with the unknown samples. When the rat alerts by scratching at a known sample, a buzzer is sounded and the rat is rewarded with a treat.

Any suspect samples are triple-checked, and if found to be positive, they're reported back to the clinics.