Avian metapneumovirus (aMPV) causes acute respiratoryinfection in turkeys with sudden onset and rapid spread in the infected flocks.Vaccinated flocks frequently showed clinical signs typical like thenon-vaccinated flocks in Egypt, this situation suggest a virulent vaccine viruswas circulating in the field. Oropharyngeal and nasal sinus swabs werecollected from 100 turkeys from 10 commercial farms with mild to moderaterespiratory signs. Virus isolation and propagation was done in SPF embryos ofchicken eggs via yolk sac inoculation and further passed in Vero cells. RT-PCRfor detection of aMPV was done on field samples as well as on virus isolates. Genotyping of viruses was done through RT-PCRtargeting Fusion (F) and the surface Glycoprotein (G) genes and partialsequencing of PCR products was used for genetic and phylogenetic analyses. Theresults were compared with two live attenuated commercial vaccines commonlyused in the field. Analysis of nucleotide and amino acid sequences for F and Ggenes indicated that they were very closely related to each other and belongingto B subtype of aMPV isolated from Europe. The Egyptian viruses were very closeto VCO3 vaccine strain indicating their possible origin. Phylogenetic analysisindicates clustering of the Egyptian field viruses with European strains of Bsubtype. These results are supporting that they may have a common progenitorfrom vaccine strains and suggesting evidence of reversion of attenuated vaccinevirus to virulence. This is the first report describing the emergence ofvaccine-derived mutants from the B subtype aMPV in broiler turkeys in Egypt.
