title: Increased virulence of modified-live infectious laryngotracheitis vaccine virus following bird-to-bird passage.
abstract: Modified-live (ML) infectious laryngotracheitis (ILT) vaccine viruses, both tissue-culture-origin (TCO) and chicken-embryo-origin (CEO), were passaged 20 times in specific-pathogen-free chickens. After serial bird-to-bird passage, increased virulence was observed for CEO virus but not TCO virus. Increased mortality and increased severity and duration of respiratory disease were observed in chickens inoculated with chicken-passaged CEO viruses; only mild respiratory disease (no mortality) occurred in chickens inoculated with chicken-passaged TCO viruses. These findings suggest that ML ILT vaccine viruses may increase in virulence after bird-to-bird passage.
authors.affiliation: Department of Microbiology, Pathology, and Parasitology, College of Veterinary Medicine, North Carolina State University, Raleigh 27606.
authors.forename: J S
authors.initials: JS
authors.lastname: Guy
authors.forename: H J
authors.initials: HJ
authors.lastname: Barnes
authors.forename: L
authors.initials: L
authors.lastname: Smith
mesh_terms: D000818:Animals; D002645:Chickens; D006566:Herpesviridae Infections / Q000382:microbiology / Q000473:pathology / Q000662:veterinary*; D001352:Herpesvirus 1, Gallid / Q000276:immunology / Q000472:pathogenicity*; D011201:Poultry Diseases / Q000382:microbiology* / Q000473:pathology; D012141:Respiratory Tract Infections / Q000382:microbiology / Q000473:pathology / Q000662:veterinary; D012692:Serial Passage; D013047:Specific Pathogen-Free Organisms; D014132:Trachea / Q000473:pathology; D014765:Viral Vaccines / Q000009:adverse effects*; D014774:Virulence
chemical_list: D014765:Viral Vaccines