The newest recruit in the fight on TB

Giant rats sniff out tuberculosis

Yashica isn't your typical laboratory technician. For one thing, there's the tail. For another, he'll literally work for peanuts.

Yashica is an African giant pouched rat, Cricetomys gambianus, that on a recent afternoon at the zoo here demonstrated his preternatural sense of smell by scuttling along a metal bench and sniffing out splotches of grenadine syrup.

This trick that amuses zoo visitors in Europe holds promise for diagnosing tuberculosis in sub-Saharan Africa. A team of scientists reported last month in the online Pan African Medical Journal that the rodents are better than human lab techs at identifying TB bacteria in a dollop of mucus.

And they're cheap.

"We have an innovative and adaptable technology that utilizes a local resource," says Bart Weetjens, founder of Tanzania-based nonprofit Apopo and a co-author of the journal paper. Apopo primarily trains African giant pouched rats to sniff land mines for de-mining activities in Mozambique, Thailand and other countries.

Mr. Weetjens says he became interested in tuberculosis a few years ago after reading a World Health Organization report about the rapid spread of the disease and learning that TB-infected saliva had a tar-like smell that could aid diagnosis. He figured if humans can smell it, rats definitely could.

Tuberculosis killed 1.7 million people in 2009, according to estimates from the WHO. Identifying infections at an early stage is crucial to curbing TB's spread in sub-Saharan Africa.

In the West, TB is often diagnosed using bacterial cultures and sophisticated blood tests. There's no money for that in much of Africa, so technicians look at slides of mucus under a microscope—a cheaper method, but one that misses a lot of cases.

When working, Apopo's rats run up and down glass enclosures filled with sputum samples, indicating when they've identified infected ones by scratching the floor with their paws. A rat takes seven minutes to work through the same number of samples as a lab technician would assess in a full day, Apopo says.

In the study, lab technicians using conventional diagnostic methods examined sputum specimens from 12,329 patients and found 1,671 positive cases of TB, or about 14% of the total. The rats, given the negative samples to evaluate, found an additional 716 TB infections, representing a 43% increase in the detection rate.

One drawback: The rats turn up many false-positive findings of TB, so the results need to be confirmed by conventional lab methods. Researchers are working on ways to reduce the number of false positives.

The study's results confirmed similar research by Apopo from 2009 in which the rats had a 44% increased rate of detection over the conventional lab technique. The researchers, including Apopo officials and Tanzanian academic and government scientists, heated the samples to destroy infectious microorganisms before they were evaluated, the study says.

"Using rats is an interesting, innovative way of thinking. They could accelerate detection compared to just microscopy" says Mario Raviglione, director of the WHO's Stop TB Department in Geneva. "The next challenge would be to see how implementation works" in real-life situations, not just in a lab, he says.

The rats' expertise takes time to acquire. The animals are weaned and socialized from the age of four weeks. Training lasts nine months, during which the rats learn to associate sniffing out certain scents with a food reward. It takes about €6,000 (about $8,518) to train one little critter, a relative bargain compared with conventional techniques. The TB-detection program is still in a research phase, Apopo says. However, the group is working with several hospitals in Africa to offer TB screening as a backup for the facilities' own lab work.

The African giant pouched rat is three feet long nose to tail on average and lives about six to eight years. They are partial to nuts and congenitally short-sighted. The rats got their start with land mines in the 1990s. Mr. Weetjens, a 44-year-old former industrial engineer from Belgium who has raised rodents since he was a boy, says he was impressed by the African rat's sense of smell and inspired by Princess Diana's anti-land-mine crusades.

In 1997, Mr. Weetjens, who now spends most of his time in Tanzania, set up Apopo to train giant pouched rats to detect TNT, an ingredient in most mines, and to deploy them on the minefields of Africa. "There was an appeal world-wide for new, sustainable detectors," Mr. Weetjens says. "We chose rats."

Apopo, which is an acronym in Dutch for Anti-Personnel Landmines Detection Product Development, is funded by the United Nations Development Programme, private foundations and governments, including Belgium and Norway. Charitable rodent fanciers can sponsor a rat and get regular updates on its progress.

Two rats can search the same area in an hour as a human de-miner can in a day. Because they weigh just two or three pounds, they don't set off the devices as they search. The rats de-mine on leashes, wearing harnesses similar in size to a Chihuahua's. When they find a mine, they scratch at the earth. Apopo has trained 150 de-mining rats.

On a recent afternoon at the Antwerp zoo, Yashica, who has been trained to sniff out sweet syrup, emerges from his home in the nocturnal enclosure to show off his olfactory skills. Two keepers put him on the bench in front of about 30 visitors. Children in the audience select where to conceal a vial of grenadine syrup. His whiskers twitching, Yashica scampers up and down the bench before scrabbling at the surface.

Time after time, he finds the prize. The crowd applauds.

Watch a video here.

Wall Street Journal

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Published: Sept. 6, 2011, 12:52 p.m.

Last updated: Sept. 6, 2011, 12:54 p.m.

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