A longitudinal study of Babesia microti infection in seropositive blood donors

Abstract

BACKGROUND Babesia infection is caused by intraerythrocytic tickborne parasites. Cases of transfusion-transmitted babesiosis have been increasingly recognized. To date, no Babesia test has been licensed for screening US blood donors. We conducted a longitudinal study to assess the course and markers of Babesia infection among seropositive donors identified in a seroprevalence study. STUDY DESIGN AND METHODS Eligible donors had B. microti indirect fluorescent antibody (IFA) titers ≥1:64. Enrollees were monitored up to 3 years, by IFA and three methods for evidence of parasitemia: B. microti nested PCR analysis (at two laboratories), hamster inoculation, and blood-smear examination. RESULTS Among 115 eligible donors, 84 (73%) enrolled. Eighteen enrollees (21%) had evidence of parasitemia for 30 total specimens (17% of 181), which were collected in 9 different months and tested positive by various approaches: PCR (25 specimens/16 persons), hamster inoculation (13 specimens/8 persons), and blood smear (1 specimen positive by all three approaches). Overall, 14 persons had ≥1 specimen with positive PCR results at both laboratories (12 persons) and/or had parasitologically confirmed infection (8 persons). Three of nine persons who had >1 specimen with evidence of parasitemia had nonconsecutive positives. Several enrollees likely had been infected ≥1 year when their last positive specimen was collected. The final three specimens for seven persons tested negative by all study methods, including IFA. CONCLUSION Seropositive blood donors can have protracted low-level parasitemia that is variably and intermittently detected by parasitologic and molecular methods. Donor-screening algorithms should include serologic testing and not solely rely on molecular testing.

Transfusion-transmitted babesiosis: is it time to screen the blood supply?

“…Consistent with other reports [6,30], this study suggested that both seropositivity and parasite DNA may persist in some donors for relatively long periods of time following infection. These findings may be of particular significance with respect to consideration of criteria for re-entry of donors who are deferred based on B. microti screening results.…”

“…PCR is more sensitive than thin blood smear and is widely considered to be a confirmatory test [29]. A negative PCR result does not rule out babesiosis because parasite concentration may be below the limit of detection, [26,30]. Although parasitemia as low as 6 parasites in a milliliter of blood can be identified in principle [26], the limit of detection for these assays varies depending on such parameters as sample volume.…”

“…Firstly, blood donors who have been very recently infected (window period) are by definition antibody negative. Secondly, people who have cleared a B. microti infection typically exhibit a measurable antibody titer lasting for months and sometimes years [6,30]. In endemic populations, the majority of seropositive individuals have been found to be PCR negative and thus are most likely to represent prior rather than active infections [34,35].…”

“…PCR is not a true gold standard for infection because a positive result may simply indicate the presence of “dead DNA” rather than active infection, although microbial DNA generally is rapidly cleared from the blood [6] [30]. Conversely, a small number of cases have been reported in which B. microti seropositive but PCR negative individuals were further tested for active infection by inoculation of their blood into hamsters from which B. microti was later recovered [30,36]. These cases demonstrate that some seropositive, PCR-negative donors harbor active B. microti infection.…”

Transmission ofBabesia microtiParasites by Solid Organ Transplantation

“…To date, no Babesia tests for screening US blood donors have been licensed by the Food and Drug Administration, and no pathogen-reduction technologies for cellular blood components have been approved ( 31 – 35 ). However, the Blood Products Advisory Committee of the Food and Drug Administration that was convened on May 13, 2015, supported the concepts of year-round B. microti serologic testing of all US blood donors and of B. microti nucleic acid–based testing of donors in selected states (details remain to be determined) ( 36 ).…”