To evaluate the extraction efficiency of viral nucleic acids from the
mussel tissue, approximately 104 plaque forming units of mengovirus
(MC0),was added as internal process control to all portions of homogenized
DT prior to proteinase K (N30 units/mg, FinnZymes, Finland)
treatment. The relative recovery efficiencies and the inhibition during
detection of HEV, RV-A and PCV2 in mussel DT, were determined in
two independent runs usingmussel DT froma confirmed negative sample
and pig slurry previously shown to contain 1.2 × 104, 5.4 × 104 and
3.8 × 105 PCR units ml−1 of HEV, PCV2 or RV-A particles, respectively.
One PCR unit was defined as the highest dilution that tested positive
by the assay. The recovery efficiencieswere calculated as the differences
in average Ct (ΔCt) values obtained from nucleic acid extracts of 140 μl
pig slurry alone and 2 g DT spiked with 140 μl slurry prior to PK treatment.
To determine the effect of PK treatment on the virus recoveries
during nucleic acid extraction, Ct values obtained from virus detection
in pig slurry by the inclusion and exclusion of PK prior to the nucleic
acid extraction were compared.