Comparative pathogenicity study of Malaysian QX-like and variant infectious bronchitis virus strains in chickens at different age of exposure to the viruses

Abstract

A recent study showed that infectious bronchitis viruses (IBV) circulating in Malaysia can be classified into 2 groups as Malaysian QX-like and variant strains. In this study, the pathogenicity of IBS130/2015 (QX-like) and IBS037A/2014 (variant) in 1-day-old and 30-day-old specific-pathogen-free (SPF) chickens were characterized. Even though both strains caused respiratory and kidney infections based on immunohistochemistry (IHC), real-time quantitative PCR (qPCR) and ciliostasis study, the results showed that QX-like strain was more pathogenic, caused higher mortality and showed higher tissue tropism to the kidney than the variant strain. On the other hand, the Malaysian variant strain although causing low or no mortality depending on the age of the infected chickens, the virus showed high tissue tropism to the respiratory tracts than the QX-like strain. In addition, IHC and qPCR indicated the presence of both IBV strains in the epithelium lining of villi of jejunum and cecal tonsil; however, no pathological changes were detected in these organs. In summary, both the Malaysian QX-like and variant IBV strains are able to infect the respiratory and kidney of chickens irrespective of the age.