A STUDY ON ISOLATION AND MOLECULAR CHARACTERIZATION OF INFECTIOUS LARYNGOTRACHEITIS VIRUS

Abstract

Avian infectious laryngotracheitis (ILT) is a severe clinical respiratory disease of chickens caused by infectious laryngotracheitis virus (ILTV) resulting in dyspnoea, bloody coughing and reduced production in commercial poultry flocks. This study was designed for molecular detection of ILTV in commercial poultry flocks showing clinical respiratory symptoms and gross pathological lesions in dead birds. Simultaneously, infected cell protein 4 (ICP4) gene of the ILTV was characterized by direct sequencing and subsequent bioinformatics assay. Field samples were collected from the 100 dead birds obtained from nine different poultry flocks of Chittagong and Gazipur district and cultivated into 9-11 day old embryonated chicken eggs through chorioallantoic membrane (CAM) route inoculation. Among them only 18 samples showed gross pathological lesions on CAM and in embryo (stunted growth of the embryo, haemorrhagic embryo, embryo mortality and pock like lesions on CAM). The eighteen samples were then subjected to mRT-PCR for screening of respiratory viruses. Out of the 18 only 12 samples showed either single or mixed (with two or three viruses) infections involving avian influenza virus (AIV), Newcastle disease virus (NDV), infectious bronchitis virus (IBV) and infectious laryngotracheitis virus (ILTV). For confirmatory diagnosis of ILTV specific PCR of ICP4 gene was performed. In both mRT-PCR and PCR assay only 3 samples (3%) were found positive for ILTV. From the PCR product direct sequencing of ICP4 gene was conducted and gene bank accession number was obtained for control vaccine (KC576526) which is a Chicken embryo origin vaccine and for field isolates (KC576525). Bioinformatics assay identified the field isolate of ILTV to be genomically similar to the vaccine isolate. Phylogenetic assay also confirmed the close relation between vaccine and field isolate of Bangladesh. From these findings it could be postulated that clinical infection of ILTV in Bangladesh were originated from Chicken embryo origin vaccines.