Résumé
A total of 986 serum samples were collected from IB non vaccinated 26 broiler farms in El- Menia; A total population of 135500 bird. All tested farms were ELISA positive for IBV antibodies. The percent of positivity were 42.86, 33.04, 48.37, 31.01, 43.09, 34.01 and 33.68 in samples from Abo- Korkas, Bani- Mazar, Dear-Mawas, EI-Menia, Malawy, Mtay and Smaloot; respectively. IB virus was successfully isolated by 4 blind passages in SPF chicken embryos, which showed curling and dwarfing and were positive to Dot-ELISA against reference antibodies IBV. Pathogenicity of the obtained virus isolate was studied in both broiler and layer chicken. In broiler chick, pathogenicity was performed in groups aged 1, 7, and 14 days. No mortality was seen in group infected at 14 day of age, while it was 8/2 chicks in both 1 and 7 days. Examined tissue sections of trachea, lung and kidney of birds at 4 and 14 days post infection in different age groups revealed severe histopathological changes especially in birds inoculated at 1 and 7 days old as compared with birds inoculated at 14 day old. In layer chicken the isolate resulted in mild respiratory manifestations [sneezing, coughing], decline of egg quantity and quality [rough shell and shell less eggs] 2 weeks after challenge as well as mortality reached 20%. Postmortem examination of succumbed broiler and layer birds revealed severe renal congestion and mild congestion in trachea and larynx