title: Titration of Marek's disease cell-associated vaccine virus (CVI 988) of reconstituted vaccine and vaccine ampoules from Dutch hatcheries.
abstract: Thirty-one outbreaks of Marek's disease (MD) were reported in the Netherlands and retrospectively analyzed. The outbreaks occurred mostly in vaccinated commercial layer and a few breeder flocks of several breeds; however, the cause of the outbreaks could not be established. Therefore, in a prospective study, the occurrence of true vaccine failures was assessed onfive hatcheries. The plaque-forming units (PFU) of MD vaccine per chicken dose were determined through in vitro assays on vacine ampoules (2 to 5 per hatchery) and samples of reconstituted vaccine (approximately 22 per hatchery). All forty reconstituted vaccine samples of hatcheries 1 and 4 showed PFU doses <10(3). In hatchery 4, 14 samples showed extreme low PFU (< or = 10 PFU). In hatcheries 2, 3, and 5, the numbers of MD vaccine suspensions with a titer > or = 10(3) PFU, which is the standard required, were 1 (5%), 17 (77%), and 3 (14%), respectively. Some vaccine ampoules showed < 10(3) PFU per chicken dose. This study shows the usefulness to assess the PFU per chicken dose of reconstituted MD vaccine and vaccine ampoules to unravel true vaccine failures, which could result in disease outbreaks in the field.
authors.affiliation: Poultry Health Centre, Animal Health Service, P.O. Box 9, 7400 AA Deventer, The Netherlands.
authors.forename: W J M
authors.initials: WJ
authors.lastname: Landman
authors.forename: S B E
authors.initials: SB
authors.lastname: Verschuren
mesh_terms: D000818:Animals; D002645:Chickens; D004196:Disease Outbreaks / Q000662:veterinary; D025922:Mardivirus / Q000276:immunology*; D008380:Marek Disease / Q000453:epidemiology / Q000276:immunology*; D022501:Marek Disease Vaccines / Q000276:immunology*; D009426:Netherlands / Q000453:epidemiology; D011201:Poultry Diseases / Q000453:epidemiology* / Q000276:immunology / Q000821:virology
chemical_list: D022501:Marek Disease Vaccines