Babesiosis Information for Health Professionals

Babesia microti is a protozoan parasite of the piroplasm family which causes a malaria-like illness in humans.  The parasite is transmitted to humans by bites from I. scapularis (the blacklegged tick or deer tick), the same vector that transmits the agents of Lyme disease, human anaplasmosis, one form of human ehrlichiosis, and a strain of Powassan virus. Babesia parasites can also be transmitted by blood transfusion.

On this page:
Clinical Presentation
Supportive Laboratory Findings


Babesiosis is a malaria-like illness caused by red blood cell parasites (Babesia spp.). It is carried by the same ticks that carry Lyme disease.

  • MDH recommends at least 2 of the following 3 tests: PCR, peripheral blood smear, or serology.
  • Recommended treatment is atovaquone + azithromycin (for mild to moderate cases) or clindamycin + quinine (for severe cases) x 7-10 days. Repeated treatment and monitoring of parasitemia levels may be necessary for patients with certain forms of immune compromise.
  • Transfusion-transmitted babesiosis can occur and should be considered in transfusion recipients who develop anemia, thrombocytopenia, or a febrile illness after receiving cellular blood products. Suspect cases should be promptly reported to associated blood banks and MDH.
Full May 6, 2011: Tick-borne Disease Health Alert


Clinical Presentation

  • The clinical spectrum ranges from mild and self-limited to serious.
  • Severe infections are most common in patients who have had a splenectomy or are otherwise immunosuppressed.
  • A gradual onset of illness may include: malaise, anorexia, and fatigue followed more acutely by fever, chills, myalgias, arthralgias, nausea and vomiting.
  • Hypotension and renal failure have been reported.
  • Cases of babesiosis acquired through blood transfusions have been documented. Include babesiosis in the rule-out for patients who develop a febrile illness with thrombocytopenia following blood transfusion. Suspected transfusion-associated babesiosis cases should be reported to MDH and the supplying blood center.

Supportive Laboratory Findings

  • Supportive laboratory findings include:
        • anemia
        • thrombocytopenia
        • hemolysis
        • hepatic dysfunction


  • In acutely ill patients, careful examination of blood smears by experienced individuals usually reveals intraerythrocytic parasites.
  • Other tests include polymerase chain reaction (PCR) and indirect immunofluorescence assay (IFA).
  • Co-infections with Borrelia burgdorferi (Lyme disease agent) or Anaplasma phagocytophilum (the agent of human anaplasmosis) can also occur, increasing illness severity.


  • Babesiosis is treated with atovaquone plus azithromycin, or with quinine plus clindamycin; treatment should be undertaken with the assistance of an infectious disease specialist.



  • Reporting Babesiosis
    Minnesota Rules Governing Communicable Diseases require health care providers to report confirmed or suspected cases of Babesiosis to the Minnesota Department of Health (MDH) within 1 working day.

MDH staff also are available to provide clinical consultation regarding diagnosis and treatment of Babesiosis and other tick-borne diseases. Call 651-201-5414 for a clinical consultation.

More information


Updated Thursday, May 29, 2014 at 09:18AM