Histopathological evaluation of trachea, lung, and mesonephros in specific pathogen free-eggs embryos inoculated for titration of avian infectious bronchitis virus M41 strain.

Infectious bronchitis, being caused by a coronavirus, is a significant disease affecting broiler and layer chickens, leading to substantial losses in the poultry industry due to the high mortality rates and decreased egg yield. Nearly 30 serotypes and 100 variants were described to date; developed vaccines are being for some severe cases, like the Massachusetts strain, to mitigate the effects. Determining the vaccinal strain's titer is crucial for creating an effective vaccine, and calculating the virus infectivity in the egg embryo is very important using dilutions ranging from 10^-3 to 10^-8, from each dilution 0.10 mL is used. The aim of this study was to determine the effects of the avian bronchitis virus injected into the allantoic cavity of ten days old embryonated eggs. Real-time polymerase chain reaction tests determined the viral load in the allantoic fluid. The embryos were removed to study gross injuries. The trachea, lung, and mesonephros were removed and submitted for histopathological studies, and nuclear factor-kappa B immunofluorescence analysis. The results revealed that the dilution of one-thousandth of the virus in the embryos caused the highest organ damage and viral replication. Varying degrees of hyperemia, edema, cellular infiltration, and degeneration were observed in the trachea, lung, and mesonephros depending on the virus dilution. This study provides valuable insights into the pathogenesis of the avian bronchitis virus, and has a potential impact on achieving an effective vaccine.