Application of a Commercial Real-Time RT-PCR Assay for Surveillance of Classical Swine Fever: Evaluation by Testing Sequential Tissue and Blood Samples

The applicability of the commercial TaqVet CSFV real-time RT-PCR assay (TaqVet CSF) as a diagnostic tool for herd surveillance of classical swine fever (CSF) was evaluated in an experimental setup on a group of 28 pigs infected with a moderately virulent classical swine fever virus (CSFV) strain of wild boar origin ('11722-WIL'). Based on the viral distribution determined in tissue by the real-time RT-PCR assay (rRT-PCR), the tonsils were found the most suitable tis- sue for CSFV detection. In the tonsils, the viral genome was detected during the incubation phase, as early as 2 days post infection (dpi), and during the clinical phase until the end of the experiment (24 dpi). In blood, viral RNA detection was delayed by 2 days compared to the corresponding tonsils. Virus was irregularly detected in muscles, indicating the poor reliability of meat for CSFV monitoring. For surveillance programmes, the effectiveness of the rRT-PCR kit was also evaluated on blood samples collected at the scale of the animal group and compared to the individual diagnosis based on analysis of tonsils. The present study indicated that, at the very early stages of infection, comparable detection efficiency was achieved by using large numbers of blood samples or smaller number of tonsils. The increased size of sampling is necessary to compensate the lower viral load observed in blood. Based on these results, testing of blood can be proposed as an acceptable alternative to tonsils for herd surveillance with the TaqVet CSF kit, providing that extended sampling is undertaken.