The parasite attacks the red blood cells. Symptoms, if any, begin with 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. It can take from 1 to 12 months for the first symptoms to appear, but less time for persons with weakened immune systems.
Laboratory diagnosis is based on identifying the parasite in red blood cells.
Complications and death are most common in persons whose spleens have been removed. Other people usually have a milder illness and often get better on their own. A combination of anti-parasite medicines can be effective in treating babesiosis. It is not known how common babesiosis is in the United States. Most people have no symptoms, and those who do are usually older persons and people who are already sick with other conditions.