95% fatality rate. This organism infects people when warm freshwater is forced high up the nose while swimming or diving, allowing it to travel along the olfactory nerve into the brain, where it feeds on and destroys brain tissue. Despite its terrifying reputation, infections are actually very rare considering how many millions of people swim in freshwater every year. The organism is known as Naegleria fowleri, often called the “brain-eating amoeba.” Photo by Francine Marciano Cabral.