First detection of Schmallenberg virus RNA in bovine semen, Germany, 2012

In analogy to the related Akabane virus, transmission of Schmallenberg virus (SBV) by contaminated semen has primarily been considered negligible. However, the potential economic consequences for stock-bull breeders prompted the investigation of reliable diagnostic methods for SBV-RNA detection in bovine semen. Twelve extraction methods were compared using a dilution series of SBV-spiked semen as well as serum and medium samples for control. The most promising methods were subsequently used with semen samples obtained in an intensive field study. In total, frozen semen from 95 SBV-seroconverted bulls collected in the field between May and November 2012 were tested for SBV-RNA with an optimised standard operating procedure. The highest diagnostic and analytical sensitivity for the extraction of SBV in semen was found for the Trizol(®) LS Reagent lysis with or without combined purification of the viral RNA with magnetic beads. A total of 29 of 766 semen batches from 11 of 95 SBV-infected bulls were PCR-positive (Cq-values 26-37). Intermittent virus excretion was observed in 2 of the bulls. SBV-RNA-positive semen was coincidentally detected with early SBV-antibodies in 4 bulls. In bulls that showed seroconversion together with consecutive positive semen batches, SBV-RNA was predominantly found in the seminal cell fraction, while in bulls with single positive results only, SBV-RNA was detected exclusively in the seminal plasma.