An otherwise-healthy 52-year-old office worker showed up to a hospital emergency department in Buenos Aires with an unshakable fever he developed the week before. Besides the high temperature, he seemed fine. So, after testing negative for COVID-19, doctors sent him home with supportive care. But the fever didn’t go away.

There was one other possibility that seemed to tick all the boxes: fever, gastrointestinal symptoms, low oxygen saturation, pulmonary edema, and shock—a hantavirus infection.