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Abstract
Infectious laryngotracheitis (ILT) is an upper-respiratory disease of poultry of worldwide distribution. The disease is caused by infectious laryngotracheitis virus (ILTV), a member of the family Herspesviridae, is characterized by acute respiratory signs, and is common in areas of intense poultry production. Currently, the main method of control of the disease is by vaccination with live attenuated vaccines. In ovo vaccination is a highly effective mass of vaccination commonly utilized in the United States, and is characterized by reduced costs in labor associated with high protective index of the chickens. In an effort to enable in ovo vaccination with ILTV, attenuation of the virus by deletion of genes associated with virulence has been performed. Recently, a recombinant ILTV depleted of open reading frame C (ORF C) gene induced protection similar to that of the TCO vaccine when delivered via eye drop in three week old SPF chickens. The objectives of this study are to evaluate the attenuation and protection efficacy of a recombinant ORF C ILT virus when delivered in ovo in the absence and presence of maternally derived antibodies; and to evaluate the protection efficacy of the recombinant ORF C virus when administered singly via in ovo, spray, or nasal-oral, and when administered in ovo followed by either spray or nasal-oral routes at eight-days of age in commercial layers. The results of this work indicate that the ORF C recombinant virus is capable of eliciting protection against ILT in chickens, however is still not sufficiently attenuated for in ovo vaccination; the protection efficacy of ORF C recombinant virus was affected by maternally derived antibodies; and priming by in ovo immunization with ORFC was essential to elicit a strong protective response to ILTV challenge.