Rabbit fever cases are on the rise as a fourth case was confirmed in Suffolk County, prompting health officials to urge the public to stay aware and take precautions. Tularemia, commonly known as rabbit fever, is a highly infectious disease caused by the bacterium Francisella tularensis. County health officials identified a tick bite as the source for one of the four local infections but have not disclosed how the other patients were exposed. 3 “Rabbit fever” cases are spiking in Suffolk County, with a fourth case now confirmed. 3 Tularemia is a highly infectious disease, also called rabbit fever, caused by the bacterium Francisella tularensis.