Avian Metapneumovirus: Current Knowledge, Critical Gaps, and Future Directions in Transmission, Pathogenesis, and Control Across Poultry Systems.

Avian metapneumovirus (aMPV) is an economically significant respiratory virus of poultry that causes major losses due to reduced egg production and increased susceptibility to secondary infections. It has global significance in poultry production systems and mainly affects turkeys, chickens, and ducks. It was first detected in South Africa in 1978 and is classified into four distinct subtypes (A-D) based upon sequence divergence of the glycoprotein (G) gene. Subtype C has historically been the dominant subtype in the US, first detected in the late 1990s, causing approximately $15 million economic loss per year in Minnesota alone. However, after a decade, aMPV re-emerged in the fall of 2023. Subtype A in California and B in North Carolina was detected for the very first time in the US, impacting multiple states, with an estimated $112 million loss in Minnesota alone. The most recent US Animal Health Association (USAHA) annual survey has now ranked aMPV as the most frequently reported issue in turkey production. Even after four decades of virus identification, areas such as transmission routes, host-virus interactions and tissue tropism within the host are not studied in detail. Addressing these gaps via current modernized research tools is crucial in minimizing the impact of aMPV on the poultry industry. Therefore, this review article summarizes current knowledge on aMPV while identifying critical research gaps and emphasizing future research directions for combating aMPV and supporting long-term sustainability of the turkey industry.