Impact Of Highly Pathogenic Porcine Reproductive And Respiratory Syndrome Attenuated Vaccine TJM Strain (HP-PRRSV TJM) Vaccination On The Immunological Response To Classical Swine Fever Vaccine

To investigate the impact of vaccination of pigs with a highly pathogenic porcine reproductive and respiratory syndrome attenuated vaccine TJM strain (HP-PRRSV TJM) on the efficacy of classical swine fever vaccine, thirty-five pigs were used in the study. The pigs were randomly divided into 7 groups, with 5 in each group. In the first group, pigs were vaccinated with HP-PRRSV TJM; the pigs in the second group were vaccinated with a classical swine fever modified-live vaccine. In both the third and forth groups, pigs were vaccinated with HP-PRRSV TJM and the classical swine fever modified-live combo vaccine. The fifth and sixth group, were negative control groups and pigs received only harvests of Marc-145 (for growth of PRRSV) and ST (for growth of CSFV) cells, respectively. The seventh group was served as non-vaccination controls. The vaccination was administered intramuscularly (i.m.) for all pigs. After vaccination, all pigs were observed for clinical manifestations and blood samples, with and without heparin, were collected on days 0, 3, 7, 10, 14, 21, and 28 post-vaccination. Heparinized blood samples were used to detect CD3~+, CD4~+, and CD8~+ T lymphocytes and white blood cell counts. Serum samples from non-heparinized blood were used to measure the antibody titers against PRRSV or CSFV. After vaccination, all pigs remained healthy with normal physiological indices. Result demonstrated that the second and the forth groups were not significant different (p<0.05) in antibody titers to CSFV, white blood cell counts and T lymphocyte subsets distribution. These results clearly indicated that HP-PRRSV TJM had no negative impact on the immune response of vaccinated pigs to classical swine fever vaccine.On day 28 post-vaccination, pigs from the 1st, 3rd, and 5th group were challenged with highly pathogenic PRRSV (HP-PRRSV). The 2nd, 4th, and 6th groups were challenged with virulent CSFV -SM strain. Following challenge, the pigs were clinically observed for diseases typical to the infection by HP-PRRSV or CSFV-SM strain. Pigs were bled for serum and lymphocytes, on days 0, 3, 7, 10, and 14 post-challenge. Serum samples were used to detected antibody titers and heparinised blood was used in white blood cell count and T lymphocyte subsets detection. The pigs were either died from the challenges or euthanized at the end of the study, and necropsies were performed and gross pathology was examined and recorded.After challenge with HP-PRRSV, pigs from the 1st and 3rd groups did not show any obvious changes in body temperature and clinical symptoms of PRRS throughout the experiment. Pigs from these groups were not significantly different (p<0.05) in antibody level, white blood cell count and T lymphocyte subsets. However, the percentages of CD3~+, CD4~+, and CD8~+ lymphocytes significantly decreased in the 5th group as compared to the vaccinate group (p<0.01). In addition, total WBC dropped in the pigs of the 5th group. Most importantly, the vaccinated pigs in the 1st and 3rd groups were protected completely, but the negative control pigs in the 5th group developed typical clinical symptoms of PRRS, with a mortality rate of 80%.After challenge with virulent CSFV-SM strain, pigs from the 2nd and 4th group did not show any obvious changes in body temperature and clinical signs of CSF throughout the experiment. Pigs from these groups were not significantly different (p<0.05) in antibody level, white blood cell count and T lymphocyte subsets. Compared to the 2nd and 4th groups, result showed that percentages of CD3+ and CD4+ lymphocytes significantly decreased in the 6th group, while there was an increase in the percentage of CD8+ lymphocytes in later period of infection. Additionally, although the level of ELISA antibody to CSFV increased in 7-14 days after challenge, total WBC dropped in the pigs of the 6th group. Similarly as in PRRSV challenge, after challenge with CSFV-SM, the vaccinated pigs in the 2nd and 4th groups were completely protected, but the negative control pigs in the 6th group had typical clinical symptoms of CSF, with a mortality rate of 100%. Pathological observations demonstrated various degree lesions, bleeding and necrosis in the most of the organs, such as lung, kidney, tonsil and lymph nodes in the pigs of the 6th group.Conclusion: vaccination of pigs with classical swine fever modified-live vaccine and the HP-PRRSV TJM at the same time, HP-PRRSV TJM did not show immunosuppression to the immune response of pigs to classical swine fever vaccine. In other hand, vaccination of CSFV vaccine also did not immunosuppress the pig immune response to PRRSV vaccine.