One person died and two others fell ill last February in New York City after contracting Leptospirosis, a disease caused by the bacteria Leptospira. The bacteria are transmitted to humans through cattle, pigs, horses, dogs and, as in this case, rats. Left untreated, Leptospira can cause kidney damage, meningitis, liver failure, respiratory distress and even death, according to the Centers for Disease Control and Prevention.