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Reporting Obligations

Confirmed and suspected cases shall be reported to the local Health Unit.

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Aetiologic Agent

Babesiosis is a tickborne disease caused by intraerythrocytic protozoan parasites of the genus Babesia. There are over 100 Babesia species known to infect vertebrates, but only a few species have been reported in humans. 

Babesia microti (B. microti) is carried by Ixodes scapularis, the blacklegged or deer tick.

Clinical Presentation

Most infections are asymptomatic, however, infected individuals may show mild to severe systemic symptoms such as fever, chills, sweats, headache, body aches, loss of appetite, nausea, or fatigue.

Babesiosis can cause a type of anemia called hemolytic anemia. Clinical symptoms of hemolytic anemia include fatigue, jaundice and dark urine (haemoglobinuria). Chronic infections may last weeks to months.

Infections can become severe and life-threatening in individuals in persons with asplenia, immunocompromise, or advanced age.

Modes of Transmission

A bite by infected tick carrying Babesia parasites that has been attached for at least 24 hours.

Babesia parasites can spread through blood transfusions, solid organ transplantation, and through congenital transmission (during pregnancy/delivery).

Incubation Period

Signs and symptoms typically occur after 1-4 weeks from a bite of an infected tick and 1-9 weeks (up to 6 months) after contaminated blood transfusion.

Period of Communicability

There is no evidence of person to person spread.

Babesia parasite can be spread by blood transfusion, solid organ transplantation and congenital transmission—from an infected mother to her baby (during pregnancy or delivery).

Risk Factors/Susceptibility

Persons with history of tick bites in an area where ticks carry Babesia parasite.

Travel to high tick prevalence or areas of known endemicity for Babesia infections.

Occupations/activities in tall grass or wooded areas where ticks reside.

Please refer to PHO’s Infectious Disease Trends in Ontario reporting tool and other reports for the most up-to-date information on infectious disease trends in Ontario.

Diagnosis and Laboratory Testing

Diagnosis is based on laboratory confirmation or supportive laboratory evidence with clinically compatible signs and symptoms of infection. 

Laboratory Confirmation

  • Detection of Babesia spp. (including B. microti, B. duncani, B. divergens, B. venatorum, and others species) nucleic acid by molecular methods from an appropriate clinical specimen (e.g., whole blood).


  • Identification of Babesia spp. organisms by microscopic examination from an appropriate clinical specimen.

Supportive Laboratory Evidence of Infection

  • Serological demonstration of B. microti total or IgG antibody titres ≥ 1:64 by indirect immunofluorescence assay (IFA).


  • Serological demonstration of B. divergens total or IgG antibody titres ≥ 1:256 by IFA.


  • Serological demonstration of B. duncani total or IgG antibody titres ≥ 1:512 by IFA

Clinical Evidence

Clinically compatible signs and symptoms are characterized by fever, chills, intense sweats, headache, dark urine, jaundice, myalgia, arthralgia, hepatosplenomegaly, anemia, and/or thrombocytopenia. Most infections are asymptomatic.

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Treatment and Case Management

Treatment is under the direction of the attending health care provider.

Patient Information

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Infectious diseases protocol 2023

Appendix 1: Case Definitions and Disease Specific Information: Babesiosis – Ministry of Health

Centers of Disease Control and Prevention: Babesiosis

Public Health Ontario: Babesiosis