Molecular Characterization of Thymidine Kinase and Glycoprotein G Genes from a Possible Vaccine Induced Infectious Laryngotracheitis Outbreak in Egypt

Infectious laryngotracheitis virus (ILTV) is a worldwide cause of acute respiratory disease in chickens. In this study, an outbreak of laryngotracheitis in commercial layers flock, Sharkia Province, Egypt in 2011 was investigated by sequencing of thymidine kinase (TK) and glycoprotein G (gG) genes. The chickens showed clinical ILTV infection, histopathological examination revealed epithelial sloughing, development of syncytical cells, heterophilic exudation with presence of eosinophilic intranuclear inclusion bodies. The virus was isolated on chorioallantoic membrane (CAM) of embryonated chicken eggs (ECE), and it induced typical pock lesions after two passages. The obtained 647 amplicon by PCR confirmed the presence of ILTV genome. Gene sequencing of TK and gG showed high genetic homology between field isolate from commercial layer flock (Sharkia-11) and vaccine strains. To our knowledge, this is the first documented ILTV outbreak attributed to vaccination with live modified ILT vaccine in Sharkia, Egypt based on sequence analysis of TK and gG genes.