In 2022, highly pathogenic avian influenza virus (HPAIV) H5N1 clade 2.3.4.4b was detected in United States (U.S.) poultry, quickly escalating into an outbreak that surpassed the 2014-15 HPAI U.S. event in scale and impact. Unlike the 2014-15 HPAI outbreak, the 2022/3/4 outbreak has included numerous detections of HPAI in previously infrequently affected commodities such as broiler chickens and commercially-raised upland game birds. In late 2023 and early 2024, an upland game bird producer in South Dakota experienced detections of HPAI across their multi-premises system. The first detection of H5 HPAIV occurred in November 2023 on a premises located in an active HPAI Control Area, and the most recent detection of HPAI in the system occurred in January 2024. We used a stochastic within-barn HPAI transmission model parameterized using premises-specific mortality data and diagnostic test results to estimate the times of HPAI introduction onto each premises and to examine the adequate contact rate and basic reproduction number within individual barns of pheasants. Across the system, the estimated transmission metrics were considerably lower than those calculated from outbreaks in other poultry species. Herein, we discuss the progression of HPAI infection in this commercial upland game bird system. Specifically, we examine potential interactions between the estimated within-barn transmission metrics, shifts in management practices that occurred during the outbreak, and other available metadata to better understand reasons behind the occurrence and dynamics of this slow-spreading H5 HPAI infection observed in commercial upland game birds.

Amos Ssematimba Secure Food Systems Team, College of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108 Department of Mathematics, Faculty of Science, Gulu University, P.O. Box 166, Gulu, Uganda Kaitlyn St. Charles Secure Food Systems Team, College of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108 Peter Bonney Secure Food Systems Team, College of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108 Marie Culhane Secure Food Systems Team, College of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108 Carol Cardona Secure Food Systems Team, College of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108

Biosecurity, mitigation, control, and post-epidemic considerations in poultry