Distribution of Infectious Bronchitis Virus Resistance in a Naïve Chicken Population

Resistance to infectious bronchitis (IB) is a polygenic trait, but little is known about how resistance distributes in the host population. In this study, a relatively large number (n = 369) of specific-pathogen-free white leghorn chickens (Gallus gallus) were challenged with an Arkansas -type virulent IB virus (IBV), and resistance was evaluated 5 days after challenge by viral load (IBV RNA) in the trachea and cecal tonsils, as well as by tracheal histomorphometry (mucosal thickness and lymphocyte infiltration). Contrary to expectations, results showed a non-Gaussian distribution of resistance of the whole population against challenge. Indeed, most chickens accumulated toward higher resistance, i.e., lower viral loads and less tracheal damage. The current results also indicated limited differences in resistance to IBV between sexes. Tracheal viral load was significantly higher in males than that in females, but tracheal damage did not significantly differ between sexes. The difference in tracheal viral load found in males and females could have implications for viral spread in commercial chicken populations.