Babesia is a parasitic protozoan that's known to cause babesiosis in humans. Babesia is spread by the bite of an infected Ixodes tick, the same tick that also transmits Borrelia burgdorferi. Babesiosis causes a form of parasitic, hemolytic disease. Symptoms include fever, fatigue, body aches, nausea, and vomiting. In severe cases, babesiosis can lead to serious health complications such as acute respiratory distress syndrome, heart failure, splenic rupture, and death.