|GARCIA, MARICARMEN - University Of Georgia|
|CHENG, YIN - University Of Georgia|
|RIBLET, SYLVA - University Of Georgia|
|SCHNEIDERS, GUSTAVO - University Of Georgia|
|VOLKENING, JEREMY - Base2bio|
Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2016
Publication Date: 9/1/2016
Citation: Spatz, S.J., Ross, T.A., Garcia, M., Cheng, Y., Riblet, S., Schneiders, G., Volkening, J. 2016. Attenuation and protection efficacy of open reading frame C (ORF C) gene deleted recombinant of infection was laryngotracheitis virus (ILTV). Journal of General Virology. 97:2352-2362. https://doi.org/10.1099/jgv.0.000521.
Interpretive Summary: A vaccine strain of infectious laryngotracheitis was generated using genetic engineering techniques. This recombinant contained a deletion in the gene encoding the virulence factor ORF- C. The complete nucleotide sequenc of this recombinant was determined. The in vitro growth characteristics of were also determined and found to be similar to that of the parental wild type strain (USDA reference strain). In chicken experiments the vaccine candidate was found to be safe and as protective against virulent challenge as the commercial vaccine strain known as tissue culture origin (TCO).
Technical Abstract: 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 'ORF 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.