Abstract
In this study, we compared three classical swine fever (CSF) outbreaks that occurred in Ibaraki Prefecture (outbreaks 1, 2, and 3 were at non-vaccinated, 10 days post-vaccination, and approximately 90 days post-vaccination, respectively). In particular, we analyzed the characteristics of outbreak 3, which occurred in a fattening pig group approximately 90 days after primary vaccination. In outbreaks 1 and 2, hemorrhagic lesions, high viral loads, and transmission to other barns were observed. In contrast, in outbreak 3 there were no hemorrhagic lesions, high Ct values, negative fluorescent antibody assay, and no CSF virus isolation, and also no viral genome were detected in tha enviroment. Additionally, no horizontal transmission to other barns was observed, and pigs with high neutralizing antibody titers were confined to the affected pig barn. Moreover, the principal lesions observed in the necropsied pigs were pneumonia and pericarditis, indicating that CSF was unlikely to have been the primary cause of death. Taken together, these findings suggest that CSF vaccination may have contributed to the suppression of pathological changes, reduction of viral replication, elimination of viruses capable of intracellular proliferation, and the prevention of environmental contamination and horizontal transmission within the farm.
