Geographic distribution of IBV lineages

ABSTRACT

Infectious bronchitis virus (IBV) is a leading cause of economic losses within the poultry industry, affecting both meat-type birds and layers. The highly contagious viral disease caused by Avian coronavirus was first described in the 1930s and still remains a global problem for the poultry industry. Infection by Avian coronavirus causes respiratory disease, nephritis, decreased egg production depending on the viral pathotype and the age of the affected flocks. Live attenuated and inactivated vaccines are used to control the disease, but poor cross-protection between different serotypes complicates control efforts. IBV exists in a wide variety of genetically distinct types and new variants are identified relatively frequently. As the emergence of new IBV variants may impede the efficacy of the vaccines, monitoring the prevalence and genetic characteristics of IBV is of utmost importance. Currently, a phylogeny-based classification system defined by Valastro and coworkers is used for the classification of IBV strains. At present, IBV strains are divided into 8 genotypes (GI-GVIII) and 39 distinct lineages (GI-1 to GI-31, GII-1, GII-2, GIII-1, GIV-1, GV-1, GVI-1, GVII-1 and GVIII-1) and a huge number of unclassified inter-lineage recombinants. Most IBV lineages are confined to specific geographic regions, and some countries report the circulation of unique lineages. In contrast, the GI-1, GI-13, GI-16 and GI-19 lineages are widely distributed. The aim of this review is to summarize the most recent knowledge about the distribution of the genetic groups of Avian coronavirus.