Viral respiratory diseases are important causes of economic losses to the poultry industry worldwide. They are responsible for impaired growth of the ocks, reduced egg production, and quality, mortality, and slaughter downgrading. In addition, they may be associated with intercurrent bacterial infections, contributing to increased economic losses (including costs for diagnoses, vaccines, antimicrobials, and treatment). Two viral respiratory diseases (the very virulent Newcastle and the highly pathogenic avian inuenza) have the potential to devastate poultry industry, but biosecurity efforts have kept the world’s main poultry-producing regions free of these pathogens. Three other viral respiratory diseases (infectious laryngotracheitis, swollen head syndrome, and infectious bronchitis [IB]) are highly prevalent and frequent in industrial poultry ocks worldwide. Of these, IB has been considered the most economically important .