A novel mitigation strategy for the prevention of transfusion-transmitted malaria.

BACKGROUND: Malaria is caused by protozoa of the genus Plasmodium and transmitted by Anopheles mosquitos. In the US, blood donors are assessed for malaria risk, including donor travel or previous residence in endemic areas and history of malaria by questionnaire and deferred for three months or three years, respectively. METHODS: The Procleix Plasmodium Assay is a qualitative nucleic acid test based on transcription-mediated amplification (TMA) for the detection of 18S ribosomal RNA of P. falciparum, P. ovale, P. vivax, P. malariae, and P. knowlesi for use on the Procleix Panther system. Analytical sensitivity was evaluated with in vitro transcripts and infected red blood cells. For clinical specificity, 12,800 individual donations and 283 pools of 16 samples from routine US donors were screened. Malaria risk was evaluated by testing 862 donors deferred for 3 years. Reactive results were confirmed with in-house real-time TMA assay and serology. RESULTS: Assay sensitivity was 8.47-11.89 RNA copies/mL and 2.10-6.82 infected red cells/mL. Specificity was 99.99% in 12,800 individual donations and 100% in 283 pools of 16. Of 862 tested deferred donor samples, one donor (0.12%) confirmed positive individually and in pools; he remained confirmed positive for 13 months. The infected donor was a prior resident of a malaria-endemic area in West Africa. CONCLUSIONS: The Procleix Plasmodium Assay showed high sensitivity and specificity and detected Plasmodium RNA in an asymptomatic presenting donor. This assay may prove helpful as a screening test versus the use of risk questions to reduce the number of donors deferred for malaria risk.

Estimated Plasmodium 18S ribosomal RNA prevalence in asymptomatic blood donors from three African countries.

BACKGROUND AND OBJECTIVES: The World Health Organization (WHO) African Region accounts for 94% of malaria cases globally, with variability recognized within endemic regions. To determine the detection rate of Plasmodium RNA in blood donors resident in malaria-endemic areas, samples from three African countries were tested using a Plasmodium nucleic acid test. MATERIALS AND METHODS: Whole blood (WB) samples collected from routine donors in Cameroon, Madagascar and Mali were shipped frozen to the United States. Samples were tested individually from WB lysates with the Procleix Plasmodium assay (transcription-mediated amplification [TMA]). Reactive samples were considered either repeat reactive or initial reactive only, depending on TMA-retest results. When available, matching plasma samples were tested for Plasmodium antibodies by enzyme immunoassay (EIA). RESULTS: Plasmodium repeat reactivity ranged from 41% (91/223 tested) in Cameroon to 12% (26/216) in Mali and 1% (3/249) in Madagascar. Initially reactive samples, where reactivity did not repeat, were identified from Cameroon (5/223; 2%) and Mali (2/216; 1%). The matched-plasma subgroup had EIA reactivity ranging from 86% (113/131 tested) in Cameroon to 59% (10/17) in Mali and 27% (68/248) in Madagascar. CONCLUSION: Plasmodium ribosomal RNA (rRNA) detection and antibody rates varied greatly in the three countries studied. Detection of Plasmodium rRNA can provide an additional tool to address malaria risk in blood donors.

Nucleic acid testing for monkeypox in United States blood donor specimens.

BACKGROUND: The 2022 multi-country outbreak of monkeypox (mpox) resulted in blood collection and public health agencies closely monitoring for changes in transmission dynamics that could pose a threat to the blood supply. While mpox virus (MPXV) is not known to be transfusion transmissible, there have been several studies demonstrating the detection of MPXV in blood. We evaluated the performance characteristics of a research use only (RUO) nucleic acid amplification test for MPXV. The assay was developed to detect MPXV DNA in plasma and serum specimens from human blood donors. METHODS AND MATERIALS: The sensitivity of the RUO MPXV Assay was determined using a synthetic DNA sequence, purified full-length genomic DNA, and a chemically inactivated virus. Specificity was determined using fresh plasma samples collected from blood donors during the outbreak. Plasma samples collected from donors considered at increased risk for exposure to mpox were also tested. RESULTS: For sensitivity, the 95% limit of detection (LOD) ranged from 0.26 copies/mL (inactivated virus) to 31.65 copies/mL (synthetic DNA) to 166.61 copies/mL (for full-length DNA). All donor samples tested with the RUO MPXV Assay were nonreactive, resulting in a specificity of 100% (95% CI, 99.93%-100.00%). DISCUSSION: The RUO MPXV Assay was developed as a potential blood donation screening assay in response to the outbreak. While not directly comparable, the 95% LOD fiducial limits obtained from partial- and full-length DNA analysis were similar to other manufacturers' MPXV assays. Additionally, this assay demonstrated high specificity for screening blood donors.

Minimal infectious dose and dynamics of Babesia microti parasitemia in a murine model.

BACKGROUND: Babesia microti is a parasite that infects red blood cells (RBCs) in mammals. It is transmitted to humans by tick bites, transfusion, organ transplantation, and congenital acquisition. Although the Babesia natural history and seroprevalence in donors have been well described, gaps in knowledge relevant to transfusion remain. STUDY DESIGN AND METHODS: Mice were infected with dilutions of parasitized blood to address the minimal infectious dose and the kinetics of parasitemia by quantitative polymerase chain reaction (qPCR) and of antibodies by enzyme immunoassay. RESULTS: In immunocompetent DBA/2 mice infected with 100 parasitized RBCs (pRBCs) and in immunodeficient NSG mice infected with 63 pRBCs, parasitemia was detectable in five of five mice each. Peak parasitemia up to 2 × 107 pRBCs/mL at 2 to 3 weeks or 5 × 108 pRBCs/mL at 6 weeks was observed for DBA/2 and NSG mice, respectively. Protracted fluctuating parasitemia was observed for 8 months in DBA/2 mice, whereas NSG mice exhibited a high-plateau parasitemia. Antibody titers continued to increase until 6 to 18 weeks in DBA/2 mice and remained high through 6 months. This study also investigated the analytical performance of Babesia assays that detect parasite DNA or RNA using a blinded panel. A Babesia assay targeting parasite RNA was approximately 10-fold more sensitive compared to qPCR targeting DNA. CONCLUSION: The mice in this study were highly susceptible to Babesia infection using as few as 1 to 2 log pRBCs and maintained chronic parasitemia. If the infectious dose in human transfusion recipients is comparably low, a highly sensitive assay targeting parasite RNA may safeguard the blood supply, particularly before antibody detection.