Molecular epidemiologic survey of infectious bursal disease viruses in broiler farms raised under different vaccination programs

SUMMARY Over a span of nearly 4 yr, 246 bursal tissue samples were collected from Brazilian commercial broiler flocks (Gallus gallus) throughout the country and imprinted to sample collection cards (Flinders Technology Associates (FTA) cards). A total of 75 infectious bursal disease virus (IBDV) strains was successfully detected from the FTA card imprints and were submitted for further identification and molecular characterization. Nucleotide and predicted amino acid sequences of the IBDV surface protein VP2 were used to identify strains of the virus and place them into phylogenetic groups. The amino acids across the hypervariable region of VP2 in this study varied, but around half of all positive samples were classified as vaccine virus. The IBD viruses fell into 3 categories: variant IBDV, classic IBDV (vaccine), and very virulent (vv) IBDV. The samples were collected according to the 3 different vaccination strategies used in broilers: vectored vaccine, antigen-antibody complex vaccine, and conventional live vaccine. The genetic profile and frequency of the strains recovered from the flocks were highly dependent on the vaccination program. This information helps us gain a better understanding of the current landscape of IBD in Brazil and provides additional scientific data to support selection of the most effective vaccination strategies, products, and practices to prevent disease.