Rajshekhar Gaji was staring at something that should not exist. Under his microscope, parasites that should have been thriving were instead dying—completely unable to survive without a protein his lab had managed to switch off.

“It was an amazing day,” said Gaji, assistant professor of parasitology at the Virginia–Maryland College of Veterinary Medicine. That moment of discovery could eventually help the 40 million Americans walking around with a microscopic parasite permanently residing in their brains.

The findings are published in the journal mSphere.