【Objective】At present, the infection type of classical swine fever in China is mainly subacute or chronic infection. The aim of this study was to investigate the differences and distribution of RNA and protein expressions in pigs infected with the intermediate virulent strain of classical swine fever virus. The results could help to elucidate the replication and distribution of the subacute disease virus and to provide technical support for the early diagnosis and prevention of classical swine fever.【Method】Using the medium virulence strain (HEBHH1/95), we successfully established a subacute CSF infection animal model. Duodenum, spleen, kidney, lung, pancreas and ileocecal samples were collected from pigs for viewing in situ hybridization (ISH), immunohistochemistry (IHC) and hematoxylin-eosin staining (HE) at 1 day post infection (dpi), 3 dpi, 6 dpi, 10 dpi, 13 dpi, 20 dpi, 24 dpi and 28 dpi. The ViewRNA ISH was used to study the dynamic distribution of viral RNA in infected tissues. Immunohistochemistry (IHC) and HE staining were used to detect the distribution of viral proteins in infected tissues and their contribution to tissue damage.【Result】The clinical score increased rapidly from 6 dpi to 10 dpi, then from 11 dpi to 26 dpi the score remained at approximately 15, until at 28 dpi clinical score peaked at 20 points. The body temperature showed an upward trend from 8 dpi to 10 dpi, and then livestock suffered from continuous fever which persisted at about 40℃ from 13 dpi to 24 dpi, thereafter, the body temperature began to fall back to about 39.5℃ before the animal died. Viral RNA were detected in duodenum, pancreas, ileocecal valve and kidney at 1 dpi and in the lungs of the bronchioles, spleen oval body at 3 dpi; Viral RNAs widely distributed in each tissue at 28 dpi, and were mainly observed in the spleen artery around the lymphatic sheath, pancreatic acinar, renal tubular with secretion function. The IHC and HE staining were used to verify the results of ViewRNA ISH in similar fields of vision. The positive signals of viral proteins and the corresponding histopathological changes of duodenum, pancreas and kidney were also detected at 1 dpi, but the viral protein and tissue pathological changes were detected in the ileocecal valve, spleen and lung at 3 dpi. Viral RNA and protein localization tended to be the same in each tissue after 3 dpi.【Conclusion】All the results showed that CSFV had an increasing virus load from 1 dpi to 28 dpi detected by ViewRNA ISH, which was in consistent with the result of IHC. Moreover, CSFV was firstly tropism to secretory cells such as pancreatic acinar, renal tubular and spleen artery at the beginning of infection (1 dpi-3 dpi), and then showed pantropically infectious to all the tissues during the infection period (6 dpi-13 dpi), and during the final stage CSFV was accumulated both around lymphocytes and secretory cells (20 dpi-28 dpi).
