ISOLATION AND MOLECULAR CHARACTERIZATION OF CIRCULATING INFECTIOUS LARYNGOTRACHEITIS (ILT) VIRUS IN EGYPT, 2018

Infectious Laryngeotrachitis (ILT) outbreaks lead to severe economic losses in the poultry industry in Egypt. At the present study, the aim was to identify the nature of a circulating ILTV (infectious laryngeotrachitis virus) strain in an outbreak occurred in Fayoum province in spring 2018. A field ILTV strain, namely Fayoum 2018, was isolated in SPF-ECE followed
by assessment of its pathogenicity in SPF chickens to calculate intra-tracheal pathogenicity index (ITPI). Thereafter, underwent molecular characterization using PCR of two fragments of ICP4 gene (688 bp and 635 bp sizes). The obtained amplicons were sequenced followed by phylogenetic analysis. The isolated Fayoum 2018 virus conferred high virulence with 0.4 ITPI. Phylogeny revealed complete identity with TCO (tissue culture origin) vaccines and the vaccine-related strains, which were previously isolated from Giza and Sharkia provinces through years 2007 to 2016. Our results indicate that Fayoum 2018 isolate retained virulence either through back-passage from bird to bird in unvaccinated flocks or flocks with un-even immunity to ILT, or retained virulence through genomic recombination with other attenuated ILT vaccine virus.