Tanzania Deploys ‘HeroRats’ to Improve Tuberculosis Diagnosis
Baraka, one of ADOPO’s landmine detection rats born in Tanzania, is described as playful and curious. He has two sisters and a brother following in his footsteps.

For months, Sharifa Shomale suffered in silence from tuberculosis, not knowing what was wrong with her. Doctors suspected a viral infection. Then an unlikely hero made a life-saving discovery: a mischievous rat named Hamisi.

DAR ES SALAAM, Tanzania—Every evening, as the call to prayer from the mosque echoes in the twilight from Manzese—a tangled Dar es Salaam slum dotted with flimsily built homes, Shomale routinely swallows a dozen pills. That’s not easy for the 38-year-old mother of three children, but it’s much better than the disease itself.

“I had all TB symptoms such as a bad cough, chest pain, and I was spitting bloody mucus,” she told Health Policy Watch, describing what she later learned were common TB symptoms along with fever, loss of appetite, and weight loss.

When Shomale became pregnant with her fourth child, her symptoms worsened. Yet doctors at Palestina hospital in Dar es Salaam, where she was receiving treatment, suspected she had contracted a viral infection.

Distraught, the visibly sick Shomale started to lose weight. At some point, she feared her unborn baby wouldn’t survive given her ill health.

“The doctor asked me to take an X-ray, but the photo did not provide any clear diagnosis, “she said.

Luckily, a friend advised her to visit the “HeroRats” TB detection facility in Dar es Salaam to have her phlegm checked. To Shomale’s surprise, an African giant pouched rat with a highly developed sense of smell detected mycobacterium within hours of investigation.

“I was very relieved, knowing that doctors would prescribe proper medication and I would stick to the treatment plan,” she said.

Shomale is not alone. Tanzania is among the world’s 30 countries with the highest burden of TB. And yet here, like in other high-burden countries, many people remain undiagnosed due to a historic lack of access to diagnostics that will simply tell them that they have the disease.

A holy grail

Quick and accurate diagnosis of TB has long been an elusive holy grail for clinicians, who describe it as a major barrier to extending treatment to the estimated 10.6 million people infected with the disease in 2021, of which only 6.4 million (60%) were actually diagnosed.

The dearth of diagnostics means that one of the world’s oldest known diseases still ranks as its deadliest too, claiming some 1.6 million lives in 2021, including 187,000 HIV positive people, according to the World Health Organisation’s 2022 Global TB report.

Diagnosis of TB via the age-old technique of sputum smear microscopy, which analyzes a sputum sample under a microscope, is still only accurate about 65% of the time, despite improvements to low-cost LED smear microscopy.

More sophisticated molecular-level diagnosis with tools like GeneXpert have been expanded under initiatives by STOP TB and the Global Fund, but still remain costly and thus out of reach to people in many low- and middle-income communities worldwide.  

Rats have a hypersensitive capacity for detecting odors 

Cars pass through Sharifa Shomale’s Manzese neighbourhood in Dar es Salaam.

In the quest to stop the spread of tuberculosis, scientists in Tanzania are taking advantage of rats’ highly developed sense of smell to detect TB bacteria more rapidly and accurately.

While rats are ill-famed for stealing food in the kitchen, nibbling expensive clothes in the wardrobe, and even spreading diseases, in Tanzania they are now gaining new stature for saving lives.

The giant African poached rats, famous for their  role in detecting landmines due to their light weight, ability to sniff out chemical compounds of explosives and ignore scrap metal, are being trained by APOPO, a Belgian non-profit organisation, to detect TB bacteria and save lives.

At ‘HeroRats’ TB detection centre in Dar es Salaam, where Shomale was successfully diagnosed, a mischievous rat nicknamed Hamisi darted between six split phlegm samples placed in a glass-sided cage.

The rodent momentarily used its nose to hover above a potential TB infection, then scratched the cage’s bottom while rubbing its front paws to confirm a positive diagnosis.

Then a researcher in a white lab coat used a giant syringe to inject a mix of crushed avocado and peanut in a small hole — a treat for the rat’s job well done.

Within minutes of scuttling over the phlegm samples, the playful rat adeptly identified five potential TB cases, APOPO’s researchers said.

Since his birth in 2018, researchers say Hamisi the rat helped save the lives of many patients including Shomale. On a typical work day, Hamisi can examine up to 100 samples before going for a rest in an open-air play cage.

“Rats are very fast, they can examine many samples within a short period of time,” said Joseph Soka, APOPO’s program manager.

Rigorous training

‘HeroRats’ begin training in their infancy.

At the age of four weeks, when he was still learning to open his eyes, Hamisi was exposed to various stimuli, and was conditioned to socialise with humans before he underwent special training to identify TB bacteria, Soka said.

The trained rats were able to screen tuberculosis samples with an accuracy of up to 85%, according to Soka. In contrast, smear microscopy, which also uses mucus from the patient’s lower respiratory tract, has a lower rate of sensitivity, ranging from 20% to 60%, he said.

In combination, the rats can help improve the pace and accuracy of sputum smear diagnosis, he said, noting that “we use the rats to re-evaluate human sputum samples from our partner clinics. One rat can screen a hundred samples in just 20 minutes.”

While a lab technologist can take a few hours peeping through a microscope to detect tuberculosis strains on a cultured phlegm sample, a trained rat can screen dozens of sample in minutes at a cost of as little as two cents ($.02) a sample screen, Soka said.

Despite their skill in detecting tuberculosis, the rats have their limitations since they cannot distinguish between different types of TB strains or identify the particularly dangerous strains that respond to only a few medications, known as multi-drug resistant (MDR) or extremely drug resistant (XDR), APOPO scientists say.

More than 579,770 sputum samples from 337,737 suspected TB cases have been screened since the project started in 2011, APOPO officials told Health Policy Watch.

For Shomale, who finally gave birth to a healthy baby boy, the TB diagnosis motivated her to immediately start treatment and reduce chances to pass on the pathogen to the rest of her family members.

“When I started taking the pills, I was no longer worried about infecting others,” she said.

A heavy burden

Tanzania is among the 30 countries with the highest burden of tuberculosis in the world. According to WHO, 142,000 Tanzanians (253 per 100,000) fell ill with TB in 2018, including 40,000 (28%) that also were reportedly living with HIV/AIDS. 

Among those, however, just 75,828 people received a lab-confirmed diagnosis. This means that some 47% of those people living with TB remained untreated, at risk of dying or transmitting the disease to friends, family and neighbors.

Health authorities in Tanzania have for decades relied heavily on smear microscopy — an outdated diagnostic technique which involves collecting and examining human sputum samples under a microscope.

Critics say positive TB cases are repeatedly going undiagnosed due to the shortage of services in rural areas and the equipment’s high margin of error.

And given the deeply rooted cultural stereotypes and low awareness of chronic diseases afflicting people in rural areas, many TB patients are stigmatized even by members of their own families – who may perceive the patients as “bewitched” rather than ill, bringing a curse upon their local community. 

On the edge of death

Mathew Kaloli writhed in pain and agony. Too frail to get on his feet, the 66-year-old fisherman from the country’s northeastern Bagamoye district suffered from chronic drug-resistant tuberculosis.

Because his diagnosis was delayed, his chances of survival were slim. “My father has lost hope of living,” his son Karim told Health Policy Watch.

An old X-ray photo showed the disease’s devastation to Kaloli’s right lung. Nestling on the chest like a delicate balloon, the lung – which should normally appear white in the photo – looked dark. The X-ray showed the landscape of the chest cavity, scrambled beyond repair.

Unlike Shomale, whose TB diagnosis was positively confirmed quickly after she sought help, Kaloli suffered in silence for many months, to the point where the disease could outwit most antibiotics. 

In an interview with Health Policy Watch, Riziki Kisonga — a pulmonologist at Tanzania’s National Tuberculosis and Leprosy programme, said the fight against tuberculosis requires rapid, innovative, and affordable detecting techniques.

“As an infectious disease that primarily affects the lungs, TB can prove fatal in the absence of timely and comprehensive treatment,” he said.

Patients need to seek treatment

Microscopic view of mycobacterium tuberculosis in the lungs.

Powerful and effective drugs are freely available in public and private health facilities across Tanzania, but TB patients often fail to show up at health facilities to receive them.

While rapid diagnosis is one barrier, it is not the only one. It is common, for instance, for some TB patients to stop taking the drugs when they start to feel better, Kisonga said, even though they may not yet be fully cured.

“If a patient takes the right medication for the right duration as advised by doctors, chances are high he/she can get cured,” he said.

Kisonga urged TB patients to get comprehensive treatment – to the end of a  course, along with using proper cough etiquette to avoid infecting others.

“Early diagnosis and effective complete treatment is the key for cure,” Kisonga said.

For Shomale, the novelty of a life-saving discovery being made by a rat has made a lasting impression..

“I always trap and kill rats at home. I never thought they would someday help doctors find a disease in my own body.”

Image Credits: ADOPO, Rwebogora, Laëtitia Dudous, Roche .

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