The oropouche virus (OROV) is primarily transmitted by Culicoides paraensis midges but transmission also occurs by some Culex mosquitoes and vertically during childbirth. Endemic in the Amazonian region of South America and the Caribbean, OROV causes dengue-like symptoms. Recent deaths from the virus have also been documented. Since OROV infection also causes mild and asymptomatic cases, transfusion-transmitted infections (TTI) may be possible, though no TTIs have been documented. To understand the potential for the OROV TTIs, researchers retrospectively screened blood samples from the 2023-2025 OROV outbreak in Brazil. Based on RT-qPCR of 661 mini-pools of 18 donor plasma samples per pool (representing 11,898 individual donations collected during the peak of the outbreak November 2023 to May 2024), 43 of 661 (6.5%) mini-pools were positive with 22 of 43 mini-pools with viral copies above 1000 per mL. Furthermore, genome sequencing of OROV revealed that asymptomatic viral infections were caused by viral strains with the same M1 linage from the Amazon responsible for the outbreak. Serology tests targeting two OROV proteins from samples collected pre- and post- outbreak confirmed an increase in seropositivity from 13% pre-outbreak among donors to 30% post-outbreak. From these studies, researchers estimated that the RNA-detectable window in donors is 5.4 days (95% C.I., 3.8 to 7.0) and that 390,000 infections occurred during this outbreak, of which 3200 cases were reported. Further surveillance of OROV and the potential as a TTI is needed.
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