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Giant Rats Are Helping Doctors in Mozambique Sniff Out Tuberculosis

A Belgian aid organization is training cat-sized African pouched rats to use their keen sense of smell to detect the presence of tuberculosis in human mucus samples.
Photo via Reuters

Ezequiel Maconha-Otenesse had night sweats, pain in his chest, and discharge spewing from his lungs when he coughed. A local hospital in Mozambique tested the 26-year-old repeatedly for tuberculosis (TB), but it took more than five months to reach a diagnosis.

"I felt weak all the time," Maconha-Otenesse told VICE News. "I was losing weight. I didn't want to eat and the doctors couldn't tell me what was wrong."


In the end, a giant rat sniffed out what his doctors could not detect.

Maconha-Otenesse was studying at the College of Veterinary Medicine at Mozambique's Eduardo Mondlane University when he fell ill. The college happens to be where Dr. Emilio Valverde, a tuberculosis expert with the Belgian aid organization APOPO, runs a lab working on a new — seemingly bizarre — way to test for the disease.

Valverde trains African giant pouched rats to sniff out tuberculosis. The cat-sized creatures — each about a foot long and weighing roughly two pounds — use their keen sense of smell to detect the presence of tuberculosis in sputum, mucus that is coughed up from the lower airways

"The rats can process more than 100 samples in 20 minutes," Valverde told VICE News. "This is work [that would take] a lab technician at least four days."

Though curable and preventable, TB remains the world's second-deadliest infectious disease after AIDS, killing an estimated 1.5 million people in 2013. More than 95 percent of cases occur in developing countries, and Mozambique — a country of 25 million people on the southeastern coast of Africa — has been hit especially hard.

Nearly 20,000 people die from TB every year in Mozambique, according to the Global Tuberculosis Report. Part of the problem is that TB often goes undiagnosed in the country — nearly two out of three people who are infected never know they have the disease.


Valverde says the current TB detection system used in labs around the world "isn't bad, it just isn't practical for a rural country with weak infrastructure and high TB rates like Mozambique."

Some hospitals use machines that cost about $17,000 to test the presence of TB bacilli, and each sample costs $10 to test. Local hospitals mostly use microscopy, a process that is less expensive but can also be less accurate. Valverde says his giant rats offer a much cheaper, more efficient alternative. Strange as it may sound, there's legitimate science to back up his claims.

Dr. Randall Reed, co-director of the Johns Hopkins Center for Sensory Biology, has researched mammalian sense of smell and the ability of animals to detect a wide variety of odorant molecules with high accuracy.

"Training an animal with a strong and reliable sense of smell to help detect disease in a rural country like Mozambique could very possibly offer an alternative solution to help detect disease," Reed told VICE News.

Historically, humans have associated rats with the spread of diseases ranging from typhus to the bubonic plague. Their droppings and hair often trigger allergic reactions in humans, and many people view them as vile and disgusting creatures.

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But Valverde trains his rats to save human lives. He claims that in 20 months his rats have accurately detected nearly 1,200 misdiagnosed cases of TB in Mozambique, and he now hopes to see the system he runs in Maputo, the capital, replicated throughout the country. Valverde is also gathering data to present an endorsement request to the World Health Organization (WHO).


Reed said that, although mammals like the African giant pouched rats may offer a valuable solution for detection of TB in rural countries with weak infrastructure, he is concerned about the practicality. "It is questionable whether this form of detection is reliable and robust under field conditions," he said.

The US Centers for Disease Control and Prevention (CDC) told VICE News that there is a very limited amount of information available about the performance of rats to detect TB. The CDC is waiting for the WHO to evaluate Valverde's data before offering any sort of endorsement.

"CDC focuses on methods that have been reviewed and approved or endorsed by a regulatory body such as the FDA or an authoritative body such as WHO," the federal agency said in a statement.

Some medical workers say various diseases have specific odors: typhoid smells like bread, one pediatric metabolic disease smells like maple syrup, liver disease can cause some people to have fishy-smelling breath, and diabetes can produce a fruity, sweet smell. One form of tuberculosis is said to smell like beer.

Valverde's African pouched rats hail from neighboring Tanzania. They undergo a rigorous training process that begins when they're about four weeks old. Right after the rat learns to open its eyes, it is introduced to various stimuli and learns how to socialize and interact with people.

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The scientists then use a clicker — similar to the tool commonly used for dog training — to create an association between food and the clicking noise.

Once the rat associates the clicker sound with a treat, it begins training on scent discrimination. The rat is offered choices of negative and positive TB samples placed under sniffer holes.

When the rat pauses above a positive sample, a lab technician will sound the clicker. The rat then goes the corner of its cage and awaits a treat.

The APOPO rats must pass an internal accreditation process before they're entrusted with diagnosing actual patients. The test is conducted under blind conditions — meaning none of the researchers or scientists involved in the actual test know ahead of time whether the samples are positive or negative. The animals must sniff out every positive sample in order to pass.

The APOPO lab has already gained the support of Mozambique's Ministry of Health, and Valverde hopes that with the backing of the WHO the program could be used internationally in countries with infrastructure and resources similar to Mozambique.

Valverde's lab currently receives samples that were already tested by the major hospital in Maputo and other collaborating TB clinics. The positive tests are used as controls, meaning rats will hear a click sound and receive a food reward when they sniff out the TB. Further testing is required in cases where the rat indicates a sample is positive but hospital lab techs have said it was negative.

Maconha-Otenesse credits the rodents with saving his life. After the rats tested his sample and diagnosed his TB, he was able to take a letter from the lab to his doctor and receive the proper medication.

"Tuberculosis kills," he said. "I never want to see anyone mistreat those rats because they saved my life."

Follow Sarah Jones on Twitter: @SarahJReports

Sarah Jones reported on health from Mozambique as an International Reporting Project New Media Fellow.