Impact of H9N2 Infection on the Pathological and Immunological Effects of the IBD Vaccine in Chicks: A Study of Vaccine Interaction and Immune Response

Abstract

Abstract Background: This study aimed to investigate the impact of H9N2 infection on the pathological and immunological effects of the IBD vaccine, and how their interaction affects the immune response to other vaccines. The objective was to determine if H9N2 infection before IBD vaccination influences the efficacy of the vaccine and if it impacts other vaccines' immune response. One hundred SPF chicks were divided into four groups in four isolators that were either H9N2 challenged, IBD vaccinated, both, or neither. Blood samples were collected weekly to measure antibody titers against IBDV, ND, H5, and H9. Cloacal swabs were taken on the 4th and 8th days post-vaccination to quantify the IBD vaccine shedding. Five chicks per group were euthanized at the 17th, 21st, and 25th days old to calculate immune organ indices and conduct histopathological examinations. Results: The study's results revealed that pre-challenge with H9N2 affected many factors. The dual-treated group had a significant decrease in the bursal index compared to the other groups. The bursal microscopical score and renal lesion score of the dual-treated group recorded a significant rise when compared to the other groups. The shedding of the IBD vaccine was negatively affected by pre-infection with H9N2, so the dual-treated group recorded a significant decrease in IBDV shedding in comparison to the IBD-vaccinated group. Additionally, the immune response against the IBD vaccine significantly decreased in the dual-treated group. Finally, there was an increase in the immunosuppressive effect of the IBD vaccine, which reflected a significant decline in the antibody titers against ND and H5 in the dual-treated group. Conclusion: The study suggests that early diagnosis of H9N2 before IBD vaccination is crucial. Pre-challenge with H9N2 significantly impacted the pathological and immunological effects of the IBD vaccine. The results showed a decrease in IBD vaccine shedding and immune response against the IBD vaccine in the dual-treated group. The immunosuppressive effect of the IBD vaccine also affected the immune response to other vaccines, as shown by the significant decline in the antibody titers against ND and H5 in the dual-treated group. Therefore, the study highlights the importance of considering H9N2 infection status before administering the IBD vaccine to ensure optimal immune response and protection.