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Screening for Babesia Microti in the US Blood Supply

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Background Babesia microti, a tickborne intraerythrocytic parasite that can be transmitted by means of blood transfusion, is responsible for the majority of cases of transfusion-transmitted babesiosis in the United States. However, no licensed test exists for screening for B. microti in donated blood.
We assessed data from a large-scale, investigational product-release screening and donor follow-up program. Methods From June 2012 through September 2014, we performed arrayed fluorescence immunoassays (AFIAs) for B. microti antibodies and real-time polymerase-chain-reaction (PCR) assays for B. microti DNA on blood-donation samples obtained in Connecticut, Massachusetts, Minnesota, and Wisconsin.
We determined parasite loads with the use of quantitative PCR testing and assessed infectivity by means of the inoculation of hamsters and the subsequent examination for parasitemia. Donors with test-reactive samples were followed. Using data on cases of transfusion-transmitted babesiosis, we compared the proportions of screened versus unscreened donations that were infectious.
Results Of 89,153 blood-donation samples tested, 335 (0.38%) were confirmed to be positive, of which 67 (20%) were PCR-positive; 9 samples were antibody-negative (i.e., 1 antibody-negative sample per 9906 screened samples), representing 13% of all PCR-positive samples. PCR-positive samples were identified all through the year; antibody-negative infections occurred from June through September.
Approximately one third of the red-cell samples from PCR-positive or high-titer AFIA-positive donations infected hamsters. Follow-up showed DNA clearance in 86% of the donors but antibody seroreversion in 8% after 1 year. In Connecticut and Massachusetts, no reported cases of transfusion-transmitted babesiosis were associated with screened donations (i.e., 0 cases per 75,331 screened donations), as compared with 14 cases per 253,031 unscreened donations (i.e., 1 case per 18,074 unscreened donations) (odds ratio, 8.6; 95% confidence interval, 0.51 to 144; P=0.05).
Overall, 29 cases of transfusion-transmitted babesiosis were linked to blood from infected donors, including blood obtained from 10 donors whose samples tested positive on the PCR assay 2 to 7 months after the implicated donation. Conclusions Blood-donation screening for antibodies to and DNA from B. microti was associated with a decrease in the risk of transfusion-transmitted babesiosis. (Funded by the American Red Cross and Imugen; number, NCT01528449 .).
Source: By Moritz ED, Winton CS, Tonnetti L, Townsend RL, Berardi VP, Hewins ME, Weeks KE, Dodd RY, Stramer SL. Screening for Babesia microti in the U.S. Blood Supply. N Engl J Med. 2016 Dec 8;375(23):2236-2245.

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One thought on “Screening for Babesia Microti in the US Blood Supply”

  1. secretscientist says:

    It would be wise and save more lives if there was a genus specific Babesia test. There is evidence that B. microti is NOT the most prevalent species of Babesia in the US, at least in sick human populations.

    The paper (link below) shows that of samples tested for Babesia, B. duncani is more prevalent than B. microti, and that B. duncani is found across the US rather than confined to the Pacific Northwest as is always stated in medical literature.

    There is also anecdotal evidence provided by tick-born-disease -treating physicians that B. duncani is more prevalent than B. microti on the East coast.

    By not testing for other species of Babesia, people receiving blood transfusions could receive the blood contaminated with other species of Babesia which could result in death.

    “Comparison of the Babesia duncani (WA1) IgG Detection Rates among Clinical Sera Submitted to a Reference Laboratory for WA1 IgG Testing and Blood Donor Specimens from Diverse Geographic Areas of the United States”

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