Babesiosis is caused by intraerythrocytic protozoan parasites of the genus Babesia. There are over 100 Babesia species but only a few can infect humans. Babesia microti is the most common infectious agent in North America. In Ontario, transmission occurs through the bite of infected blacklegged ticks called Ixodes scapularis or deer ticks.
The overall risk of acquiring babesiosis in Toronto is low but is increased if participating in activities in wooded and brushy areas.
For general information about tick-borne diseases including epidemiology and prevention, visit TPH’s Tick-Borne Diseases of Public Health Significance (TBDoPHS) webpage.
Most infections are asymptomatic.
Symptoms usually occur one to four weeks after a tick bite or one to nine weeks (and up to six months) after a contaminated blood transfusion.
Symptoms include:
Babesiosis may cause hemolytic anemia resulting in fatigue, jaundice and dark urine. Chronic infection may last weeks to months.
Risk factors for severe illness include:
Refer to Public Health Ontario’s summary table for distinguishing clinical symptoms between tick-borne diseases of public health significance.
Babesia parasites are mostly spread to humans by the bite of an infected tick. The tick usually needs to be attached and feeding on a person’s blood for at least 24 hours to transmit the parasite.
Less commonly, the parasite can spread through blood transfusions, solid organ transplantation, and through congenital transmission during pregnancy/delivery.
Testing is indicated for individuals with compatible clinical symptoms and a relevant exposure history (e.g., outdoor activity in an endemic area, tick bite(s), if known).
Microscopy is the preferred diagnostic test for babesiosis. Turnaround time is up to 24 hours from receipt at the Public Health Ontario Laboratory.
Babesia PCR may be helpful to diagnose cases with submicroscopic parasitemia or atypical morphology. This test is referred out, and samples are sent to the National Microbiology Laboratory (NML) in Winnipeg.
Babesia serology should not be used for routine diagnosis of acute babesiosis. Its role is primarily limited to individuals linked to a case of transfusion-transmitted, transplant-associated, or congenital babesiosis with negative microscopy and PCR results. This test is referred out, and samples are sent to the National Reference Centre for Parasitology (NRCP) in Montreal.
Refer to the following Public Health Ontario Laboratory resources for more information:
For patients with symptomatic babesiosis, consultation with an infectious diseases specialist is recommended. Treatment recommendations may include oral atovaquone and oral azithromycin for 7-10 days. Clindamycin plus quinine can be considered as an alternative.
For US CDC treatment guidance, see Clinical Care of Babesiosis (US CDC).