Pathological Investigation of Infectious Laryngotracheitis (ILT) in Chickens of Bangladesh

Respiratory diseases are the most common cause of death in a poultry flock in Bangladesh. Knowledge of the avian respiratory system is essential for developing a health monitoring plan for a poultry flock, recognizing problems that may occur, and taking action to correct them. Infectious laryngotracheitis (ILT) is a major viral respiratory disease of chickens. Besides chickens, pheasants and peafowls can be naturally infected by contact with chickens actively shedding infectious laryngotracheitis virus (ILTV). This study was to taken to identify the clinical signs, gross and histopathology in natural cases of infection in the field. Clinical signs of ILT were found nasal discharge, conjunctivitis and reduced egg production. In severe cases, gasping, coughing, expectoration of bloody mucus and marked dyspnea were found which may lead to suffocation. Death was observed due to obstruction of the trachea by hemorrhage or exudates. 20% mortality was recorded in the field in this study. Gross lesions were most consistently observed in the larynx and trachea, even though the conjunctiva and other respiratory tissues. Tissue changes in tracheal and laryngeal tissues were mild, with only excessive amount of mucus, conjunctivitis, sinusitis, and mucoid tracheitis, or severe, clotting blood with hemorrhage and diphtheric changes. Inflammation extended down the bronchi into the lungs and air sacs. Edema and congestion of the epithelium of the conjunctiva, infraorbital sinuses and lungs were observed in mild forms of ILT. Epithelial hyperplasia, metaplasia, multifocal degeneration and, in a few epithelial cells, nucleic inclusion bodies were detected in the trachea. Multinucleated cells (syncytia) were formed and lymphocytes, histiocytes, and plasma cells migrate into the mucosa and submucosa. Later, cell destruction and desquamation were resulted in a mucosal surface either covered by a thin layer of basal cells or lacking any epithelial covering. Blood vessels within the lamina propria with severe congestion and serofibrinous exudated were observed in the tracheal lumen and lungs.