Table 2.

Quantification of risk of transfusion transmitted babesiosis and assay development.

	Overview	Study Design	Major Finding	Reference
Efficacy of detection methods	Development of prototype EIA	Development of protype EIA using recombinant, immunodominant peptides BMN1-17 and MN-10.	69/72 (95.9%) IFA samples detected by EIA. 98/107 (91.5%) positive IgG blot samples detected using EIA. 53/63 (84.1%) positive IgM blot samples detected by EIA. All 12 PCR positive samples detected.	Houghton et al. Transfusion 2002 [36]
	Development of a real time PCR assay for detection of B. microti	Investigational study combining spiking experiments, probit analysis, and performance assessment using clinical sample panels.	Spiking experiment positive rate of detection: 445 copies/mL: 100%; 44.5 copies/mL: 97.5%; 4.45 copies/mL: 81%. The blinded probit analysis: detection rate: 95%: 12.92 parasites/2 mL; 50%: 1.52 parasites/2 mL of whole blood; Clinical samples: 13 of 21 samples were positive. Healthy donors: 0 of 48 positives.	Bloch et al. Transfusion 2013 [37]
	Development and validation of cobas Babesia assay (Roche diagnostics)	Evaluation of analytical performance of molecular assay (cobas Babesia assay, Roche diagnostics) targeting 4 major species of Babesia using individual and pooled samples Spiking experiments, cross-reactivity, and donor samples assessed to determine performance characteristics of the assay.	Limit of detection: B. microti 6.1 infected red blood cells (iRBC)/mL; B. duncani 50.2 iRBC/mL; B. divergens 26.1 iRBC/mL; B. venatorum 40.0 iRBC/mL. Specificity: ID-NAT: 99.999% (95% CI:99.996, 100); MP-NAT (6 donations): 100% (95% CI: 99.987, 100).	Stanley et al. Transfusion 2021 [38]
Parasite persistence in blood products	Babesia tolerance of storage conditions	B. divergens inoculated into blood bags containing leukoreduced red blood cells (RBCs) and stored at 4 °C for 0 to 31 days. Parasite viability assessed through interval sampling.	Viability maintained through 31 days of refrigerated storage despite altered morphology, reduction in parasitemia and lag to exponential growth.	Cursino-Santos et al. Transfusion 2014 [39]
Animal models for determining the risk of TTB.	Immunopathogenesis	6 Rhesus macaque monkeys were transfused with either hamster or monkey-passaged B. microti–infected red blood cells to simulate TTB	First detectable parasitemia 4 days in monkey-passaged cells (vs. 35 days in hamster passaged cells). Window period (detectable parasitemia by qPCR to detected antibody response): 10 to 17 days. Multilineage immune activation albeit not NK or Treg cells.	Gumber et al. Transfusion 2016 [40]
	Minimum infectious dose and kinetics of parasitemia	Murine model infected with different dilutions of B. microti parasitemic blood. Responses compared between immunocompetent and immunodeficient mice.	Peak parasitemia: 2 × 107 pRBCs/mL at 2 to 3 weeks and 5 × 108 pRBCs/mL at 6 weeks immunocompetent and immunodeficient, respectively. Chronic infection: fluctuating parasitemia in immunocompetent mice; high plateau parasitemia in immunodeficient mice. Minimum infectious dose: 100 parasitized RBCs in immunocompetent mice and 63 parasitized RBCs in immunodeficient mice; able to establish infection in all mice in respective cohorts.	Bakkour et al. Transfusion 2018 [35]

Abbreviations: IFA—indirect fluorescent antibody; EIA—enzyme immunoassay; PCR—polymerase chain reaction; TTB—transfusion-transmitted babesiosis; IDT—individual donor testing; MP-NAT—minipool nucleic acid testing.