Variability Assessment of California Infectious Bronchitis Virus Variants.

Area of Science:

• Veterinary Virology
• Molecular Epidemiology
• Avian Pathology

Background:

• Infectious bronchitis virus (IBV) causes significant economic losses in the poultry industry.
• California variant 1737 (CA1737) and California variant 1999 (Cal 99) have been identified as prevalent IBV genotypes in California.
• Understanding the genetic variability of IBV strains is crucial for disease control.

Purpose of the Study:

• To compare the genetic variability of prevalent California IBV variants (CA1737, Cal 99) with reference strains (M41, Ark) in the S1 gene hypervariable region.
• To investigate the evolution of IBV subpopulations during serial passages in embryonated chicken eggs.

Main Methods:

• Analysis of 1444 infectious bronchitis (IB) cases diagnosed between 1997 and 2012 in California.
• Epidemiologic analysis to identify IBV outbreak peaks and prevalent genotypes.
• Serial passaging of IBV strains (CA1737, Cal 99, M41, Ark) in embryonated chicken eggs.
• Sequencing and analysis of S1 gene hypervariable regions to detect genetic subpopulations and nonsynonymous changes.

Main Results:

• CA1737 and Cal 99 were the most prevalent IBV genotypes during the study period, with outbreaks mainly in broiler chickens aged 35-49 days.
• M41 showed low variability with the predominant population persisting.
• Ark exhibited high variability, with the original field sequence becoming extinct after the first passage.
• Cal 99 and CA1737 displayed intermediate variability, with distinct subpopulations emerging and evolving during passaging.

Conclusions:

• The California IBV variants CA1737 and Cal 99 exhibit intermediate genetic variability compared to Massachusetts 41 and Arkansas strains.
• Serial passaging reveals distinct evolutionary dynamics of different IBV genotypes.
• The findings contribute to understanding the genetic diversity and evolution of IBV in poultry populations.