Rats have long been guilty of spreading disease. But now they’ve gone into the diagnosis side. Because rats can be trained to spot tuberculosis—and to do it better than conventional techniques. The finding is in the American Journal of Tropical Medicine and Hygiene.

TB is the number-one infectious disease killer in the world. Early detection saves lives. But the most common way to diagnose TB, visually checking sputum samples for the microbe that causes the disease, requires sophisticated equipment and trained personnel. And it’s not all that accurate.

That’s why the rats come in. The critters are easy to train and can smell chemicals present with a TB infection. So scientists sent more than 20,000 sputum samples from 10,000 patients in Tanzania to be analyzed microscopically. They then presented the same samples to the rats. The results: the fancy microscopes found about 13 percent of the patients to be TB-positive. The rats identified an additional 620 cases, boosting the detection rate by 44 percent.

That may not sound like much, but remember a person with TB can infect another dozen or so people over the course of a year. So that’s more than 7000 people that could be saved by a rat.