Babesiosis is most commonly spread to humans by the bite of a tick infected with the Babesia parasite. Babesiosis is spread by deer ticks, which are carried mainly by deer, meadow voles, and mice. Deer ticks also spread Lyme disease. Humans can be infected with both babesiosis and Lyme disease at the same time. Babesiosis in otherwise healthy individuals are usually asymptomatic.
Early symptoms are tiredness, loss of appetite, and a general ill feeling.
As the infection progresses, these symptoms are followed by fever, drenching sweats, muscle aches, and headache. The symptoms can last from several days to several months. Rarely, the illness can be life-threatening. Symptoms can take anywhere from 1 to 12 months to develop after the bite of an infected tick, but less time in persons who have weakened immune systems. Babesiosis is diagnosed by examining the blood under a microscope.