Immune response to Massachusetts and Brazilian variant strains of infectious bronchitis virus in broiler chickens

This study aimed to assess the virulence and immune response in broiler chickens vaccinated with the Massachusetts H120 strain and the BR Variant strain of bronchitis via serological, histomorphometric, and histopathologic analyses of the tracheal mucosa. We used 162 one-day-old chicks, housed in random blocks within two temperature and light-controlled enclosures. Both the Massachusetts H120 and BR Variant strains were administered via ocular and spray routes. Blood samples were collected at four, seven, 14, 21, and 28 days of age for humoral response analysis using ELISA, from which we 2024derived an immune response profile for each vaccine group based on the geometric mean titer (GMT). Tracheal fragments were collected at four, seven, and 14 days of age and processed using standard histological techniques. Histomorphometric measurements were analyzed using ANOVA and Tukey's post hoc test (p < 0.05). The GMTs for both H120 and BR strains across the different administration routes were comparable in terms of humoral immune response. We observed significant histomorphometric differences (p < 0.05) among the strains and vaccine administration routes. The H120 group exhibited higher lesion scores across all ages. The results indicate that the BR Variant strain elicits a lower post-vaccinal reaction and provides superior homologous protection under the challenges of poultry farming in Brazil.