Clinical/serological outcome in humans bitten by Babesiaspecies positive Ixodes ricinusticks in Sweden and on the Åland Islands

The risk of contracting babesiosis after a tick bite in Sweden and on the Åland Islands, Finland, is unknown. We investigated clinical and serological outcomes in people bitten by Ixodes ricinusticks positive for Babesiaspecies. Ticks, blood and questionnaires were obtained from study participants in Sweden and on the Åland Islands. Sixty-five of 2098 (3.1 %) ticks were positive by real-time PCR. Three Babesiaspecies were detected, Babesia microti(n = 33), B. venatorum(n = 27) and B. capreoli(n = 5), the latter species not known to cause human infection. Half (46 %) of the BabesiaPCR-positive ticks also contained Borreliaspp. Fifty-three participants bitten by a BabesiaPCR-positive tick and a control group bitten by a BabesiaPCR-negative tick were tested for B. microtiIgG antibodies by IFA. The overall seroprevalence was 4.4 %, but there was no significant difference between the groups. None of the participants seroconverted and no participant with a BabesiaPCR-positive tick sought medical care or reported symptoms suggestive of babesiosis. Given the prevalence of Babesiain I. ricinusticks in southern Sweden and on the Åland Islands, babesiosis should be considered a possible diagnosis in symptomatic residents who seek medical care following tick exposure.