title: Epidemiology of recent outbreaks of infectious laryngotracheitis in poultry in Australia.
abstract: OBJECTIVE
  Over the past 3 years, numerous outbreaks of infectious laryngotracheitis (ILT) have occurred in poultry in Australia. The objectives of this study were to identify the viral strains involved in the recent outbreaks and to determine possible epidemiological links between these outbreaks.
  
  
  METHODS
  A combination of polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analyses of several genes of the ILT virus was used to identify genetic differences in field/vaccine ILT virus isolates. In a previous study, these procedures had demonstrated five classes (1-5) in Australia.
  
  
  RESULTS
  Analysis of 92 field ILT viruses demonstrated four new classes: 6, 7, 8 and 9. Class 6 was responsible for four outbreaks in one Victorian broiler company and demonstrated to be distinct from other Australian strains of ILT. Class 7 was the Nobilis ILT vaccine (Intervet Pty Ltd). Class 8 was responsible for the majority of the outbreaks in New South Wales and was phylogenetically close to class 7. On one occasion, classes 7 and 8 were identified in an outbreak on a Victorian farm that had used the Nobilis ILT vaccine. Class 9, also phylogenetically close to classes 7 and 8, was found only in New South Wales. The previously identified class 2 was also found to be responsible for a large number of outbreaks, mainly in Victoria.
  
  
  CONCLUSIONS
  The results demonstrate that, epidemiologically, most outbreaks of ILT in New South Wales are unrelated to those in Victoria and suggest a link between classes 8 and 9 and the Nobilis ILT vaccine (class 7).
authors.affiliation: School of Veterinary Science, The University of Melbourne, 250 Princes Highway, Werribee, Victoria 3030, Australia. hblacker@unimelb.edu.au
authors.forename: H P
authors.initials: HP
authors.lastname: Blacker
authors.forename: N C
authors.initials: NC
authors.lastname: Kirkpatrick
authors.forename: A
authors.initials: A
authors.lastname: Rubite
authors.forename: D
authors.initials: D
authors.lastname: O'Rourke
authors.forename: A H
authors.initials: AH
authors.lastname: Noormohammadi
mesh_terms: D000818:Animals; D002645:Chickens; D004196:Disease Outbreaks / Q000662:veterinary; D005260:Female; D006566:Herpesviridae Infections / Q000453:epidemiology / Q000517:prevention & control / Q000662:veterinary*; D001352:Herpesvirus 1, Gallid / Q000302:isolation & purification; D022283:Herpesvirus Vaccines / Q000008:administration & dosage; D008297:Male; D009517:New South Wales / Q000453:epidemiology; D016133:Polymerase Chain Reaction / Q000662:veterinary; D012150:Polymorphism, Restriction Fragment Length; D011201:Poultry Diseases / Q000453:epidemiology*; D014136:Tracheitis / Q000453:epidemiology / Q000662:veterinary*; D014739:Victoria / Q000453:epidemiology
chemical_list: D022283:Herpesvirus Vaccines