Effective surveillance for early classical swine fever virus detection will utilize both virus and antibody detection capabilities.

Early recognition and rapid elimination of infected animals is key to controlling incursions of classical swine fever virus (CSFV). In this study, the diagnostic characteristics of 10 CSFV assays were evaluated using individual serum (n = 601) and/or oral fluid (n = 1417) samples collected from -14 to 28 days post inoculation (DPI). Serum samples were assayed by virus isolation (VI), 2 commercial antigen-capture enzyme-linked immunosorbent assays (ELISA), virus neutralization (VN), and 3 antibody ELISAs. Both serum and oral fluid samples were tested with 3 commercial real-time reverse transcription-polymerase chain reaction (rRT-PCR) assays. One or more serum samples was positive by VI from DPIs 3 to 21 and by antigen-capture ELISAs from DPIs 6 to 17. VN-positive serum samples were observed at DPIs ≥ 7 and by antibody ELISAs at DPIs ≥ 10. CSFV RNA was detected in serum samples from DPIs 2 to 28 and in oral fluid samples from DPIs 4 to 28. Significant differences in assay performance were detected, but most importantly, no single combination of sample and assay was able to dependably identify CSFV-inoculated pigs throughout the 4-week course of the study. The results show that effective surveillance for CSFV, especially low virulence strains, will require the use of PCR-based assays for the detection of early infections (<14 days) and antibody-based assays, thereafter.