Attenuation and Protection Efficacy of ORF C Gene-Deleted Recombinant of Infectious Laryngotracheitis Virus

J Gen Virol. 2016 Sep;97(9):2352-2362. doi: 10.1099/jgv.0.000521. Epub 2016 Jun 9.


Infectious laryngotracheitis (ILT) is a highly contagious respiratory disease of chickens caused by infectious laryngotracheitis virus (ILTV). The disease is controlled by the use of live-attenuated vaccines. Previously we reported the complete nucleotide sequence of the ILTV vaccine strain (TCO) and identified a nonsense mutation in the gene encoding the ORF C protein. This suggested that the ORF C protein might be associated with viral virulence. To investigate this, an ILTV recombinant with a deletion in the gene encoding ORF C was constructed using the genome of the virulent United States Department of Agriculture (USDA) challenge strain (USDAch). Compared to the parental virus, the ΔORF C recombinant replicated in chicken kidney (CK) cells with similar kinetics and generated similar titres. This demonstrated that the ORF C deletion had no deleterious effects on replication efficacy in vitro. In chickens, the recombinant induced only minor microscopic tracheal lesions when inoculated via the intra-tracheal/ocular route, while the parental strain induced moderate to severe microscopic tracheal lesions, even though virus load in the tracheas were comparable. Groups of chickens vaccinated via eye-drop with the ∆ORFC-ILTV were protected to levels comparable to those elicited by TCO vaccination. To our knowledge, this is the first report that demonstrates the suitability of ∆ORFC as a live-attenuated vaccine to prevent the losses caused by ILTV.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Cell Line
  • Chickens
  • Gene Deletion*
  • Genes, Viral
  • Herpesviridae Infections / pathology
  • Herpesviridae Infections / prevention & control
  • Herpesviridae Infections / veterinary*
  • Herpesviridae Infections / virology
  • Iltovirus / genetics*
  • Iltovirus / immunology*
  • Iltovirus / pathogenicity
  • Iltovirus / physiology
  • Poultry Diseases / pathology
  • Poultry Diseases / prevention & control*
  • Poultry Diseases / virology
  • Trachea / pathology
  • Treatment Outcome
  • Vaccines, Attenuated / administration & dosage
  • Vaccines, Attenuated / genetics
  • Vaccines, Attenuated / immunology
  • Vaccines, Synthetic / administration & dosage
  • Vaccines, Synthetic / genetics
  • Vaccines, Synthetic / immunology
  • Viral Load
  • Viral Vaccines / administration & dosage
  • Viral Vaccines / genetics
  • Viral Vaccines / immunology*
  • Virulence Factors / genetics*
  • Virus Replication


  • Vaccines, Attenuated
  • Vaccines, Synthetic
  • Viral Vaccines
  • Virulence Factors