Scoring of Histopathological Lesions and Evaluation by In Situ Hybridization in Pigs Infected with Classical Swine Fever Virus at Six Farms in Tochigi Prefecture

Abstract

The JPN/1/2018 strain of classical swine fever virus (CSFV) currently circulating in Japan is classified as having moderate pathogenicity. Within the last five years, six distinct CSF outbreaks have been documented on pig farms in Tochigi Prefecture. Histopathological analysis was conducted on 23 pigs diagnosed with CSF, and lesion severity was systematically scored to assess pathological features and explore possible underlying factors. Notably, hemorrhagic and lymphocyte-depleted lesions were frequently identified in the spleen, kidneys, and superficial lymph nodes. Nonetheless, the analysis did not reveal any definitive factors influencing the lesion scores. When employed alongside immunohistochemistry (IHC), in situ hybridization (ISH) exhibited sensitivity superior to IHC. Furthermore, ISH alone detected positive signals indicative of encephalitis, thereby establishing a link between CSFV infection and encephalitic lesions.