Infectious bronchitis virus has the ability to change rapidly in nature. Traditionally, IBV strains are classified into different serotypes based largely on virus-neutralisation (VN) tests in several laboratory systems. Determining the serotype of an IBV strain can be important because it is generally accepted that different serotypes do not always cross-protect.
Strains of IBV can also be classified based on genetic characteristics of the spike glycoprotein gene, which for the most part correlates with serotype.
Electron micrograph of Infectious Bronchitis virus particles Cook, J.K.A. (1983). Isolation of a new serotype of infectious bronchitis‐like virus from chickens in England. Veterinary Record, 112, 104‐105.