Isolation and identification of a subtype C avian metapneumovirus in chickens in Jiangsu, China

Avian metapneumovirus (aMPV) is a viral pathogen that mainly causes respiratory signs and drops in egg production in turkeys, chickens, and ducks. Here, an aMPV subgroup C (aMPV/C) strain, designated GX22-01, was isolated and identified from severe respiratory disease in broiler breeder chickens in 2022 in Jiangsu, China, as evidenced by indirect immunofluorescence and western blotting using specific anti-viral protein antibodies and by sequence analysis of viral nucleoprotein (N) gene. N gene sequencing indicated that the GX22-01 strain shares a high identity (94.3%-99.8 %) with aMPV/C isolates, especially with Chinese aMPV/C isolates from ducks and chickens, which are divided into aMPV/C cluster through N gene-based phylogenetic analysis. The aMPV/C GX22-01 strain was continuously passaged in Vero cells and the viral titers approximately reached 10^6.0 TCID₅₀/0.1 mL. Pathogenic analysis showed that aMPV/C GX22-01 strain inoculation caused respiratory signs in 2-week-old specific-pathogen-free (SPF) chickens and resulted in pathogenic damage in tracheae and lung tissues, accompanied by positive viral signals using indirect immunohistochemistry. These results provide epidemiological and pathogenic data for developing effective measures against aMPV/C infection in China.