Abstract: 【Objective】 The aim of this study was to explore the pathogenicity of Bovine viral diarrhea virus (BVDV) and the immune effect of BVDV E2 recombinant protein in New Zealand White rabbits.【Method】 The BVDV virus was purified and its titer was determined by Reed-Muench method. In the pathogenicity analysis test, 10 New Zealand White rabbits were randomly divided into infection group and control group, with 5 rabbits in each group. The infected group was challenged with 1 mL purified BVDV virus (nasal drip 500 μL, ear edge intravenous injection 500 μL), and the control group was treated with equal volume of normal saline, once a day for 3 days. The clinical symptoms and body temperature were observed every day. Blood samples were collected from auricular vein on 6, 9, 12, 15 and 17 days after inoculation. On the 17th day of infection, nasal swabs were collected for RT-PCR identification. After collection, trachea, lung, spleen and small intestine tissues were dissected and pathological sections were prepared to observe the pathological changes. In the immune effect evaluation experiment, 10 New Zealand White rabbits were randomly divided into the immune group and the control group, with 5 rabbits in each group. New Zealand White rabbits were immunized with E2 recombinant protein (1 mg/rabbit) mixed with adjuvant by intramuscular multi-point injection, and the control group was immunized with equal volume of normal saline, two immunizations were given at an interval of 14 days.Serum samples were collected on 0, 7, 14, 21 and 28 d after the first immunization, and the levels of specific antibodies against recombinant protein were detected by indirect ELISA. On the 28th day after the first immunization, nose swabs were collected for RT-PCR identification, and trachea, lung, spleen and small intestine tissues were collected for pathological sections to observe the pathological changes and immunohistochemistry detection.【Result】 The titer of the purified virus was 4.16×10⁶ TCID₅₀/mL. Compared with control group, some New Zealand White rabbits in the infected group had reduced activities and slightly reduced food intake within 6 days, and gradually returned to normal after 6 days. Diarrhea symptoms appeared on the 13th day of infection, and the body temperature increased slightly on the 5th day, but all fluctuated within the normal range. Compared with control group, white blood cells and platelets in infection group were significantly and extremely significantly decreased on the 6th and 9th day of challenge (P<0.05 or P<0.01). On the 12th, 15th and 17th days of challenge, white blood cells, platelets and lymphocytes in the infection group were extremely significantly decreased (P<0.01). RT-PCR test of nasal swabs was positive, and histopathological changes of trachea, lung, spleen and small intestine were mild to severe. The results of indirect ELISA showed that the titer of serum antibody was 1:16 to 1:32 on the 7th day after the first immunization. The nasal swabs of New Zealand White rabbits in the immune challenge group were negative by RT-PCR. Histopathological observation showed slight histopathological changes in trachea and lung in the immune challenge group. On the 28th day after the first immunization, the titer of serum antibody was 1:256 to 1:512. Immunohistochemical test results showed that the results were negative in the immune group and positive in the control group.【Conclusion】 A model of disease in New Zealand White rabbits was established by intranasal and auricular vein injection of BVDV, BVDV E2 subunit vaccine could stimulate the body to produce specific antibodies and play the role of immune defense.

Key words: Bovine viral diarrhea virus(BVDV); New Zealand White rabbits; immunohistochemistry; subunit vaccine