Are Babesia a risk factor for blood products in an alpine area?

After malaria, babesiosis is the second most common transfusion-transmitted vector-borne disease. This study investigates seroprevalence rates to Babesia divergens and B. microti in the Tyrol and assesses the risk of blood products being contaminated by either agent.

The area of investigation comprises the Austrian part of Tyrol. A number of 988 sera were tested for IgG antibodies against B. divergens and B. microti by in-house immunofluorescence assays (IFA). IFA-slides were tested by using commercially available hyperimmunesera.

Collection of questing ticks was performed in summer 2009 by about 120 volunteers among hunters at 25 sampling sites over a period of three months by flagging.

Of 988 sera, 21 (2.1%) were positive in IFA against the B. divergens-complex at titres of 1:128 or higher and 5 (0.5%) were positive in IFA against B. microti.

Under the presumption of a long-lasting immune response we can expect 0.5 (±0.2, 95%) seroconversions against B. divergens per 10.000 persons per year. For B. microti the same calculation results in 0.1 (±0.08, 95%) seroconversions per 10.000 persons per year. B. divergens The risk of a blood donation being contaminated by B. divergens or B. microti is estimated to be 24.2 and 5.8 per 100,000 blood donations.

The present study shows that the local population comes into seroreactive contact with at least one member of the B. divergens-complex and - to a lesser extent - B. microti. To our knowledge, it is the first demonstration of B. venatorum in the Tyrols. Thus, and as vector-borne diseases are subjected to dynamic changes, we recommend re-assessment of the risk of transfusion-mediated infections on a regular basis and to introduce PRT for blood components like platelets.