title: Reversion to virulence of a subtype B avian metapneumovirus vaccine: is it time for regulators to require availability of vaccine progenitors?
abstract: Empirically derived live avian metapneumovirus (AMPV) vaccines developed during the late 80s and early 90s have generally performed well in controlling turkey rhinotracheitis. Nonetheless, unstable attenuation was previously demonstrated in an AMPV subtype A vaccine. Until now this had not been investigated in subtype B vaccines due to lack of any similar availability of a vaccine progenitor or its sequence. The publication of the full genome sequence for the VCO3 vaccine progenitor facilitated a conclusive investigation of two AMPVs isolated from poults on a farm which had been vaccinated with VCO3 derived vaccine. Full genome sequencing of the isolates and their comparison to sequences of the vaccine and its progenitor, confirmed their vaccine origin. After determining the absence of extraneous infectious agents, one of these virus isolates was inoculated into 1-day-old turkeys in disease secure isolators and shown to cause disease with a severity similar to that caused by virulent field virus. This suggests that instability in live AMPV vaccines may be generalized and highlights the need for availability of vaccine progenitor sequences for the field assessment of all live viral vaccines.
authors.affiliation: Department of Animal Medicine, Production and Health, University of Padua, Viale dell'Università, 16, 35020 Legnaro (PD), Italy.
authors.forename: M
authors.initials: M
authors.lastname: Cecchinato
authors.affiliation: Department of Veterinary Medical Sciences, University of Bologna, Via Tolara di Sopra, 50, 40064 Ozzano Emilia (BO), Italy. Electronic address: elena.catelli@unibo.it.
authors.forename: E
authors.initials: E
authors.lastname: Catelli
authors.affiliation: Department of Veterinary Medical Sciences, University of Bologna, Via Tolara di Sopra, 50, 40064 Ozzano Emilia (BO), Italy.
authors.forename: C
authors.initials: C
authors.lastname: Lupini
authors.affiliation: Department of Veterinary Medical Sciences, University of Bologna, Via Tolara di Sopra, 50, 40064 Ozzano Emilia (BO), Italy.
authors.forename: E
authors.initials: E
authors.lastname: Ricchizzi
authors.affiliation: Department of Veterinary Medical Sciences, University of Bologna, Via Tolara di Sopra, 50, 40064 Ozzano Emilia (BO), Italy.
authors.forename: S
authors.initials: S
authors.lastname: Prosperi
authors.affiliation: Department of Infection Biology, University of Liverpool, Leahurst Campus, Neston, Cheshire CH64 7TE, United Kingdom.
authors.forename: C J
authors.initials: CJ
authors.lastname: Naylor
mesh_terms: D000818:Animals; D016679:Genome, Viral; D029121:Metapneumovirus / Q000235:genetics* / Q000276:immunology; D018184:Paramyxoviridae Infections / Q000517:prevention & control / Q000662:veterinary*; D011201:Poultry Diseases / Q000517:prevention & control*; D017422:Sequence Analysis, DNA; D014422:Turkeys; D014613:Vaccines, Attenuated / Q000276:immunology; D014765:Viral Vaccines / Q000276:immunology*
chemical_list: D014613:Vaccines, Attenuated; D014765:Viral Vaccines
keywords: Avian metapneumovirus; Environmental vaccine identification; Farm disease; Reversion to virulence; Vaccine progenitor availability