ABSTRACT
Infectious laryngotracheitis virus [ILTV] was detected in chicken laryngeal and tracheal samples from outbreaks in 4 governorates in Egypt [Kalubia, Sharkia and Gharbia]. The viral antigen was detected by AGPT and FAT in 7 isolates, which subjected to physicochemical, biological characterization and pathological investigations. Isolated ILTV produced characteristic pock lesions on CAM of Embryonated Chicken Eggs [ECEs] and characteristic intranuclear inclusion bodies by direct FAT and histopathological examination in infected CAM and tracheal smears. The isolate S3 was the most pathogenic strain [by pathogenicity test of the isolates on ECEs and susceptible chickens] and had one more protein band than the other isolates as compared to the standard virus [by SDS-PAGE]. Ether sensitivity and thermo-stability of the isolated viruses at 56[degree sign]C indicated that the local isolate loss its infectivity to ECEs after treatment with ether for 24 hours and 15 min. at 56 [degree sign]C as well as the standard control ILTV. By cross neutralization, the results revealed that the isolated strains appeared to be related to the standard ILTV through neutralization index between each other. Infectivity titre of the virus was increased by passaging it in SPF eggs till reaching the highest titre by the 5th passage