Avian metapneumovirus infections in poultry flocks in Poland - molecular evidence for emerging divergence from vaccine strains.

Despite use of aMPV vaccines, clinical signs of disease caused by aMPV infection with field strains were widely reported in poultry production in Poland.The strains detected formed a distinct cluster of "Polish field strains".Two complete aMPV-B genomes revealed several non-synonymous mutations, especially in G and SH genes, that may account for the poor protection provided by the vaccines.Phylogenetic analysis of two Polish complete genomes revealed a significant genetic distance from available aMPV-B strains.