Infectious laryngotracheitis in layer birds from Tamil Nadu, India

Infectious laryngotracheitis (ILT), caused by Gallid herpesvirus1, is one among the respiratory diseases of poultry gradually spreading worldwide, including Indian subcontinent. Present study was carried out to identify the pathogen from the suspected cases of the disease. The tracheal tissue samples (pooled) were collected from the birds suspected to have died of ILT from 26 commercial poultry farms located in and around Namakkal district of Tamil Nadu state of India. On post-mortem examination, haemorrhagic caseous exudate and fibrinous pseudo-membrane adhered to tracheal mucosa were noticed. A total of 22 farms were found positive through PCRs targeted against ICP4 gene and the thymidine kinase (TK) gene followed by confirmation through sequencing. Histopathology examination revealed decilliation, hyperplasia, degeneration and/or loss of tracheal epithelium with severe submucosal edema. There was infiltration with numerous lymphocytes, macrophages and plasma cells in milder infections, whereas presence of fibrinous exudates admixed with numerous erythrocytes and inflammatory cells like heterophils and lymphocytes were seen indicating the severe acute form of the disease. A fibrinous pseudomembrane was seen firmly attached to the inflamed and necrotic mucosa in subacute cases. Further, virus was isolated from randomly selected 5 PCR positive tracheal tissue samples in embryonated chicken eggs through chorioallantoic membrane (CAM) route. The typical pock lesions were observed on CAM along with engorged blood vessels and thickening of the membrane. Present study has reported the disease ILT among poultry flocks in the Namakkal district of Tamil Nadu and raises the concern for thorough investigation of the nature of prevailing pathogen in the region.