Anatomopathological, ultrastructural, immunohistochemical and molecular characterization of infectious laryngotracheitis outbreaks in poultry farms in Egypt (2018–2020)

Infectious laryngotracheitis (ILT) is a severe respiratory disease, which causes high morbidity and mortality in affected birds. In our study, ILT were reported in 42 farms from nine governates over two years (2018–2020) that showed clinical signs of ILT including dyspnea, blood expectoration of, excessive lacrimation, rattling, conjunctivitis. The disease affected different chicken breeds and age groups despite vaccination with licensed and commonly used vaccines. Samples of larynx, trachea, lungs and air sacs were examined and collected for histopathological, ultrastructural, immunohistochemical examination and molecular detection. Gross examination of laryngeal and tracheal lumen revealed different types of exudate varied from catarrhal to fibrinonecotric, also pneumonia and airsacculitis were detected. Histopathological examination showed different alternation in larynx, trachea, lung and air sac as characteristic syncytial cells containing intranuclear inclusion body hanged in fibrinoheterphilic exudate that precent in laryngeal, tracheal, bronchial and parabronchial lumen and air sacs. Tracheal lesion scoring system was used to categorize the severity of lesion in different governates. Tracheal lesion score showed that 6.02%, 26.5%, 43.3% of the birds exhibited mild, moderate, and severe changes, respectively, while 24.18% of the birds exhibited very severe changes. Furthermore, severe cases were related to the Qalyubia , Fayoum then Sharkia Governorate. Moreover, immunohistochemistry was used to detect viral particles in syncytial cells, inflammatory cells beside epithelium of trachea and lung. Transmission electron microscopy enabled the detection of virus particles and demonstrated that heterophils could be infected. PCR targeting a region in the thymidine kinase gene and glycoprotein gJ gene confirmed the presence of infectious laryngotracheitis ILT virus-specific DNA. In conclusion, anatomopathological, immunohistochemical, molecular and ultrastructural findings showed increased of ILTV severity in Egypt. Larynx, trachea, lungs and air sac should be collected and examined that aid in diagnosis. Importance of good biosecurity level to be considered.