Babesia is a tick-transmitted protozoan of major concern in the transfusion community as a result of the organism’s ready transmission through transfusion. B. microti and B. duncani (the two main species in the U.S.) are transmitted from mice to humans by the tick species Ixodes. Like malaria, babesiosis is primarily an infection of red blood cells.

Babesia has a LONG asymptomatic incubation period during which the organism can be transmitted through transfusion (numerous cases of transfusion transmission have been documented, including fatal cases). Infection in immunocompromised blood recipients can have devastating consequences. Most Babesia infections are seen in a fairly geographically limited area in the U.S., however (specifically, “…in the Northeast and upper Midwest, especially in parts of New England, New York state, New Jersey, Wisconsin, and Minnesota” per the CDC). 

The U.S. FDA has classified Babesia as a “relevant transfusion-transmitted infection” (RTTI), and, in a guidance from May 2019, FDA is “recommending” Babesia testing for all blood donors in 14 U.S. states and the District of Columbia (the full list: Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, Wisconsin and Washington, D.C.). Donors are testing using an FDA-approved nucleic acid test for Babesia.

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