Trained rats can detect tuberculosis.

Nice when they’re fighting the spread of disease rather than the other way around. Science News looks into how to train giant, explosive-sniffing rats to find early signs of TB infections:

Since 2000, the international nonprofit APOPO has partnered with Tanzania’s Sokoine University of Agriculture to train African giant pouched rats (Cricetomys ansorgei) to pick up the scent of TNT in land mines. By 2016, the animals had located almost 20,000 land mines in Africa and Southeast Asia.

To help more people, Georgies Mgode, a zoonotic disease scientist at Sokoine, and colleagues began training the rats to recognize tuberculosis, an infectious disease that killed about 1.6 million people in 2016. The most common diagnostic tool — inspection of patients’ sputum under a microscope — can miss infections more than half the time. More accurate technologies are costly or still in testing.

“Every disease, anything organic, has a smell,” says Mgode. Mycobacterium tuberculosis, the bacterium that causes TB, emits 13 volatile chemicals that set it apart from other microbes, he and colleagues reported in 2012. Training a rat to be a TB sniffer, recognizing those smells in phlegm, takes about nine months.

Microscopy detected TB in 8,351 samples. The rats detected those, plus 2,745 more, later verified by other methods. The animals did especially well on samples from young kids, who often cough up less phlegm for testing and have low bacterial counts.