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Babesiosis is caused by microscopic parasites that infect red blood cells and are spread by certain ticks. In the United States, tick-borne transmission is most common in particular regions and seasons: it mainly occurs in parts of the Northeast and upper Midwest and usually peaks during the warm months.

Although many people who are infected with Babesia do not have symptoms, for those who do effective treatment is available. Babesiosis is preventable, if simple steps are taken to reduce exposure to ticks.

Babesia microti is transmitted by the bite of infected Ixodes scapularis ticks—typically, by the nymph stage of the tick, which is about the size of a poppy seed.

The following ticks are known to transmit babesiosis in humans:

  • Blacklegged (deer) Tick  (Ixodes scapularis)


Signs + Symptoms

Many people who are infected with Babesia microti feel fine and do not have any symptoms. Some people develop flu-like symptoms such as:

  • Fever
  • Chills
  • Sweats
  • Headache
  • Body Aches
  • Loss of Appetite
  • Nausea & Vomiting
  • Fatigue

Because Babesia parasites infect red blood cells, babesiosis can cause hemolytic anemia (from the destruction of red blood cells). Babesiosis can be a severe, life-threatening disease, particularly in people who do not have a spleen, have a weak immune system for other reasons (such as cancer, lymphoma, or AIDS), have other serious health conditions (such as liver or kidney disease), or are elderly.



Most asymptomatic persons do not require treatment. Health care providers may consult CDC staff about whether to treat someone who has babesiosis, what type(s) of therapy to use, how to monitor the status of the infection, and how long to treat. Treatment decisions should be individualized, especially for patients who have (or are at risk for) severe or relapsing infection.

For ill patients, babesiosis usually is treated for at least 7-10 days with a combination of two prescription medications — typically either:

  • Atovaquone PLUS Azithromycin; OR
  • Clindamycin PLUS Quinine (this combination is the standard of care for severely ill patients).