Infectious Bronchitis Virus in Poultry: Molecular Epidemiology and Factors Leading to the Emergence and Reemergence of Novel Strains of Infectious Bronchitis Virus

Infectious bronchitis virus (IBV) is a coronavirus that causes an acute and highly contagious disease in chickens. The virus can cause substantial economic losses throughout the poultry industry worldwide. It can affect the upper respiratory tract and the reproductive tract, and some strains can cause nephritis. The causative agent IBV is an RNA virus with great ability for mutation and recombination, thus capable of generating new virus strains that are difficult to control. There are many IBV strains found worldwide, including the Massachusetts, 4/91, D274, and QX-like strains that can be grouped under the classic or variant serotypes. In addition, new types of the virus continue to arise due to mutations and recombination events in the viral genome and even more factors, making this virus difficult to identify and extremely difficult to control. Surveillance and identification of IBV types are extremely important for control of the disease and the advancement of molecular methods has aided in this pursuit. Genetic typing of IBV, which involves reverse transcription polymerase chain reaction amplification and sequence analysis of the S1 glycoprotein gene, has revolutionized diagnosis and identification of this virus by making it possible to type and compare the relatedness of a large number of virus isolates in a short period of time. Several conventional and molecular diagnostic methods have been described for the diagnosis of IB in chickens. “All-in/all-out” operations of rearing along with good biosafety measures form the basis of prevention, whereas vaccination forms the backbone of IB control program. Both live and inactivated (oil emulsified) conventional vaccines are available. The new generation vaccines (recombinant and vector-based) developed against locally prevailing IBV strains may be more helpful and avoid the reversion of virulence in live vaccine viruses.