Surveillance for Avibacterium paragallinarum in autopsy cases of birds from small chicken flocks using a real-time PCR assay

Infectious coryza is a severe respiratory disease of chickens associated with large economic losses in affected commercial flocks. The fastidious causative pathogen, Avibacterium paragallinarum, is difficult to recover and identify, resulting in delayed diagnosis and enhanced spread of the agent. Small poultry flocks are increasingly common in rural and suburban environments. We assessed the frequency of A. paragallinarum using real-time PCR and clinical conditions present in samples from such flocks submitted to the California Animal Health and Food Safety Laboratory System (Davis, CA) in 2018. From the 294 samples collected for our study, 86 (30%) were PCR-positive for A. paragallinarum. Juvenile birds (≤1 y) were significantly more likely to be PCR-positive (p = 0.017), and birds diagnosed with respiratory disease had lower Ct values (p = 0.001) than those without. Concurrent infections were also identified, including with Mycoplasma gallisepticum (18.6%), M. synoviae (18.6%), infectious bronchitis virus (12.8%), and infectious laryngotracheitis virus (7.0%). Only 46.5% of PCR-positive chickens had antemortem respiratory signs, making endemic infections in these flocks highly likely. Our study demonstrates that A. paragallinarum is present in small-flock operations including those without respiratory disease and may present a risk for airborne pathogen transmission to commercial poultry operations.