Infectious bronchitis virus Mass-type (GI-1) and QX-like (GI-19) genotyping and vaccine differentiation using SYBR green RT-qPCR paired with melting curve analysis.

Infectious Bronchitis Virus (IBV) is a highly contagious virus of chicken, causing huge economic losses in the poultry industry. Many genotypes circulate in a given area, and optimal protection relies on vaccination with live attenuated vaccines of the same genotype. As these live vaccines are derived from field viruses and circulate, understanding the prevalence of different IBV genotypes in any area is complex. In a recent study, the genome comparison of an IBV QX vaccine and its progenitor field strain led to the identification of vaccine markers. Here we developed a simplex SYBRgreen RT-qPCR assay for differentiation between QX-like field and vaccine strains and a multiplex SYBRgreen RT-qPCR assay for IBV genotyping with melting curve analysis, as each virus produced distinct and reliable melting peaks. Both the simplex and the multiplex assays showed excellent efficiency, sensitivity and specificity representing a low cost diagnostic tool for IBV genotyping and vaccine differentiation.