A Retrospective Analysis of Select Respiratory Pathogens in Backyard Chickens in Pennsylvania

Backyard chickens have become more popular in the United States in recent years. Due to the private nature of owning backyard chickens, information on these flocks is difficult to obtain. Given the large scale of the commercial poultry industry in the United States, and particularly in Pennsylvania, understanding disease risks that backyard chickens face is vital for public health and the health of commercial flocks. Respiratory pathogens are of particular concern for backyard chickens because they are common and can spread rapidly among birds and cause severe disease. Mycoplasma synoviae (MS), Mycoplasma gallisepticum (MG), Avibacterium paragallinarum, and infectious bronchitis virus (IBV) are among the most common respiratory pathogens detected in backyard flocks. This retrospective cross-sectional study analyzed 835 backyard chicken necropsy submissions to the Pennsylvania Animal Diagnostic Laboratory System from September 1, 2019, to August 31, 2024, for the presence of these four pathogens. Avibacterium paragallinarum was found to be the most common pathogen detected, with 229 positive submissions (229/589, 39%). MS, MG, and IBV had 148 (148/502, 29%), 71 (71/631, 11%), and 71 (71/467, 15%) PCR-positive submissions, respectively. A total of 381 submissions were tested for all four pathogens of interest, and 245 of these submissions (64%) were positive for one or more pathogens. Seasonality was significant for detection of A. paragallinarum and IBV, with the greatest number of detections occurring in the summer and fall. Detections were predominantly in birds from southeastern Pennsylvania, coinciding with the most poultry-dense region of the state.