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Analytical Chemistry


Rodents on the job

by Melody M. Bomgardner
April 25, 2016 | A version of this story appeared in Volume 94, Issue 17


Tuberculosis-sniffing rats save time, work for peanuts

Credit: Apopo
A smeller rat: Apopo’s training and research center in Tanzania.
This image shows animal trainers in Tanzania with a tuberculosis-detecting African giant pouched rat.
Credit: Apopo
A smeller rat: Apopo’s training and research center in Tanzania.

To ferret out false-negative tests for tuberculosis, some clinical labs in Africa are turning to specially trained assistants: African giant pouched rats. In Dar es Salaam, Tanzania, and other locations, the rodents sniff out infections with a high degree of speed and accuracy, according to Apopo, the nonprofit organization that runs the training operation.

The skilled rodents are in demand. In cities that do not have modern lab equipment and instead rely on traditional smear tests, 50% or more of positive TB cases are not caught. Apopo-trained rats are tasked with rescreening negative results. Their success rate is closer to 80%, says Charlie Richter, Apopo’s U.S. director.

“We put them in a special cage, where they can sniff 10 samples at once. They can go really, really fast.” Richter says. In Tanzania, that has translated to 7,445 additional TB patients identified since 2007.

See how African giant pouched rats are trained to detect tuberculosis in samples from patients.
Credit: APOPO HeroRATs/YouTube

The rats take about nine months to fully train—and almost all of the trainees successfully graduate from the program. Because they live about eight years and cost very little to feed—including peanut butter rewards—the rats are very cost-effective, Richter adds.

The giant rats are now being put to work in clinics in Mozambique, a country with one of the highest TB prevalence rates in the world. Apopo is gathering additional data in the hopes that rats can be promoted to first-line screeners.

The organization’s scientists don’t really know why the rats do such a good job. “We don’t know what the molecules are that they are detecting—possibly it is a volatile given off by the TB bacteria itself,” Richter suggests. When asked what the patients think of the technology, he acknowledges, “We don’t tell patients they were diagnosed by rats.”

Lab mice sport tail tattoos

You don’t have to be a TB-sniffing rat to have an important job in science. If you are the lab mouse with the fastest time in the maze, you want to make sure everyone knows it. Now, a device developed by Somark Innovations can tattoo identifying marks right on your tail.

Credit: US Patent & Trade Office
Nice ink: Somark’s patented system for mouse tail tattoos.
This patent diagram shows Somark’s system for tattooing the tails of lab mice.
Credit: US Patent & Trade Office
Nice ink: Somark’s patented system for mouse tail tattoos.

No one has asked the mice, but researchers who work with lab animals say this method promises to be less stressful for everyone.

“It looks awesome,” says J. Alex Grizzell, a neuroscientist who works with rodents at the University of Tennessee, Knoxville. “I’ve had to use ear clip methods and, when that’s problematic, a simple Sharpie—always a problem for long-term identification.”

Somark’s Labstamp system includes a cartridgelike container that secures the mouse—and its tail—in place. The cartridge with mouse is then placed in a printing device loaded with a needle and ink. According to the company, UV-fluorescent inks are available—handy for dark-colored mice.

See how the Somark Labstamp mouse tattoo system works.
Credit: APOPO Somark/YouTube

Melody Bomgardner wrote this week’s column. Please send comments and suggestions to



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