| In the United States, more than 90% of chicken meat is produced in the southeastern states, and most egg production resides in the eastern half of the country and Texas. Several molecular epidemiological studies have indicated that most infectious bronchitis (IB) virus (IBV) isolates obtained from outbreaks of respiratory disease in these regions correspond to Ark-type IBV in spite of extensive vaccination programs which include IBV ArkDPI-derived vaccines. Accumulating evidence suggests that Ark-type strains may have a distinct capacity to circumvent preventive measures. Two strategies by which Ark-type IBV strains may maintain a high prevalence in commercial chickens are: (1) Unusually high genetic and phenotypic variability, and (2) synergism with... |
