title: Demonstration of loss of attenuation and extended field persistence of a live avian metapneumovirus vaccine.
abstract: A live A type avian metapneumovirus (AMPV) vaccine which had been shown to be highly protective and short lived in experimental conditions was found to persist for longer periods in the field and to be associated with disease. Previously other factors such as possible secondary pathogens and management considerations had made it impossible to conclude whether the observed disease was a result of an increase in the vaccine virulence. In this study, an AMPV was isolated from poults on a farm which had been vaccinated with the same live A type vaccine. Full sequencing of the isolate, the vaccine and the vaccine progenitor confirmed its vaccine origin and further showed that generation of the vaccine had only involved nine substitutions of which three coded for amino acid changes. The isolated virus was inoculated into 1-day-old turkey poults in disease secure isolators and shown to cause disease with a severity similar to that caused by virulent field virus. Only two coding mutations were associated with this reversion to virulence.
authors.affiliation: Department of Veterinary Public Health and Animal Pathology, Faculty of Veterinary Medicine, University of Bologna, Via Tolara di Sopra, 50, 40064 Ozzano Emilia (BO), Italy. catelli@vet.unibo.it
authors.forename: Elena
authors.initials: E
authors.lastname: Catelli
authors.forename: Mattia
authors.initials: M
authors.lastname: Cecchinato
authors.forename: Carol E
authors.initials: CE
authors.lastname: Savage
authors.forename: Richard C
authors.initials: RC
authors.lastname: Jones
authors.forename: Clive J
authors.initials: CJ
authors.lastname: Naylor
mesh_terms: D000818:Animals; D004196:Disease Outbreaks; D029121:Metapneumovirus / Q000276:immunology* / Q000472:pathogenicity*; D018184:Paramyxoviridae Infections / Q000276:immunology* / Q000662:veterinary* / Q000821:virology; D011201:Poultry Diseases / Q000276:immunology* / Q000473:pathology / Q000821:virology; D012367:RNA, Viral / Q000032:analysis / Q000276:immunology; D020545:Respiratory Mucosa / Q000473:pathology / Q000821:virology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014422:Turkeys / Q000276:immunology* / Q000821:virology*; D014613:Vaccines, Attenuated / Q000276:immunology; D014765:Viral Vaccines / Q000276:immunology*
chemical_list: D012367:RNA, Viral; D014613:Vaccines, Attenuated; D014765:Viral Vaccines