History of Avian Metapneumovirus Subtype C in the United States.

Since its first detection in turkeys in South Africa in the late 1970s, avian metapneumovirus (aMPV) has emerged as a major pathogen of concern for poultry worldwide, causing acute respiratory disease with significant economic consequences. The virus has spread throughout every continent besides Australia, with distinct subtypes (A-D) identified in different regions and hosts. In the United States, the emergence of subtype C in the mid-1990s led to widespread outbreaks in turkeys and established an endemic presence for almost a decade. Eradication efforts took years of surveillance, molecular characterization of the new subtype, concentrated region-wide eradication plans, and vaccine development before they were fully successful. The recent detection of new subtypes (subtypes A and B) in the United States in 2024, after nearly two decades of aMPV-free status, underscores the continual need for vigilant monitoring and adaptive management of this highly contagious and impactful respiratory disease. This review seeks to cover the historical emergence, progression, and eradication of aMPV subtype C (aMPV/C) in the United States, while drawing on lessons learned from the epidemic for the broader global avian industry.