Rats sniff out TB next door

Known for detecting land mines, the rodents could also help detect the world’s second-deadliest infectious disease, reports the International Centre for Journalists and the UN Foundation press fellow KATYA CENGEL.

On a Friday morning at a laboratory in Mozambique, 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 10 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. “One rat can evaluate more samples in 10 minutes than a lab technician can evaluate in a day.”

Training rats to detect TB is a relatively new endeavour for Apopo.

The Belgian nonprofit organisation best known for using rats to find land mines began using TB rats in Tanzania in 2008 and in Mozambique in 2013.

Currently, the animals work in 21 medical centres in Dar es Salaam, Tanzania, and double-check 75 percent of potential TB samples from medical centres 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, some 58 000 of them in Mozambique, according to the World Health Organization (WHO)—is badly in need of an innovative, rapid and affordable detection technique.

“We know that we need a new approach in the diagnosis of TB, so this could be one of the approaches,” said independent TB and HIV specialist Gaël Claquin.

Rats seem to be a promising solution: In the first 16 months of the Maputo programme, they evaluated samples from roughly 12 500 patients. Of those, 1700 had been found positive at the health clinics. The rats detected another 764 patients, an increase in the detection rate of around 44 percent, according to Apopo.

Missed Cases

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.

“More than half the cases are missed,” said Claquin, a former national programme officer for TB at the WHO in Mozambique.

 It is 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.”

How It Works

After undergoing nine months of training at Apopo headquarters in Morogoro, Tanzania, the rats are put to work in Maputo or Dar es Salaam. In Maputo, Emilio Valverde 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 recognise the scent of specific molecules that reflect the presence of the tuberculosis germ—not the explosive vapour 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.

“Each rat costs around $6700 to $8 000 to train, but relatively little to maintain over their six-to-eight-year life span,” said Valverde.

In comparison, the new rapid diagnostic test GeneXpert costs $17 000 per device and between almost $10 and $17 per test.

Rodent Drawbacks

Smelling out sickness is becoming more popular, explained Stewart Reid, with the Centre for Infectious Disease Research in Zambia.

There has been preliminary research using honeybees or even electronic instruments—like an e-nose—to detect TB. Research has also indicated that dogs can detect cancer through smell.

Ivan Manhiça, with the Mozambique Ministry of Health, appreciates the rats’ contribution to TB detection, especially their speed and affordability.

Still, the rats cannot differentiate between TB and a drug-resistant strain of the disease, said Claquin.

Ensuring that the rats’ training is consistent and high quality is critical, as is completing key clinical trials necessary to obtain World Health Organization endorsement.

Increasing the size of the now relatively small project would also be difficult, said Jennifer Topping of the UN Development Programme in Mozambique.

At present the samples are collected weekly from clinics in Maputo and brought to the rats at Eduardo Mondlane University’s College of Veterinary Medicine.

After a hard day’s work, Tariq and his companions are placed back in individual cages, where they wash their faces and get on with the ordinary task of being a rat. —NationalGeographic .com