Rapid detection of subtype B avian metapneumoviruses using RT-PCR restriction endonuclease digestion indicates field circulation of vaccine derived viruses in older turkeys

Live vaccines predominantly control avian metapneumovirus (AMPV) infection in the poultry industry but vaccine virus can be found for extended periods after application. The most frequently used AMPV vaccine in Italy, VCO3 subtype B, was shown to contain a unique Tru9I restriction endonuclease (RE) site within the amplicon resulting from of a commonly used AMPV diagnostic RT-nested PCR. Analysis of European and database logged subtype B AMPV sequences confirmed the sequence only occurred in the VC03 vaccine. A subsequent RT-PCR-RE study of field samples, collected from turkeys between 2007 and 2012, detected subtype B vaccine derived strains in twelve of ninety tested samples, collected from birds below 12 weeks of age.