Characterization of a Moderately Virulent Pigeon Paramyxovirus Type 1 (Subgenotype VI.2.1.1.2.2) Strain: Genetic Evolution and Pathogenicity in Pigeons

Pigeon paramyxovirus type 1 (PPMV-1) poses a significant threat to pigeon farming in China, and understanding its biological characteristics and pathogenicity is critical for vaccine development and disease control. In this study, we characterized a PPMV-1 QY strain, performed full-length genome sequencing, and constructed a phylogenetic tree based on the F gene. Then, the biological properties and the pathogenicity of the QY strain were assessed and evaluated in vitro and in vivo. The results showed that phylogenetic analysis classified the QY strain within subgenotype VI.2.1.1.2.2, the predominant circulating strain in China. The QY strain exhibited a 50% egg infectious dose (EID₅₀) of 10^-6.8/0.1 mL, mean death time (MDT) in chicken embryos of 68.7 ± 2.1 h, and intracerebral pathogenicity index (ICPI) in one-day-old chicks of 1.12, which indicate it is a moderately virulent strain. Animal experiments showed that the QY strain resulted in a mortality rate of 66.7% in healthy pigeons. Necropsy findings included cerebral congestion and swelling, hemorrhagic glandular stomach papillae, tracheal ring hemorrhages, and duodenal congestion and swelling. Histopathological analysis revealed extensive inflammatory infiltration in the lungs and liver, widespread intestinal erosion, and severe necrosis of splenic red pulp cells. In conclusion, the QY strain belongs to subgenotype VI.2.1.1.2.2 and exhibits moderate virulence, causing high mortality and severe pathological lesions in infected pigeons. These findings provide valuable insights into the pathogenicity of PPMV-1 and the specific mutations in the F protein can serve as potential attenuation targets in vaccine development against the emerging subgenotype VI.2.1.1.2.2.