Molecular detection of the Marek disease virus in slaughtered broiler in Semnan slaughterhouse

Marek's disease (MD) is a highly contagious neoplastic disease in poultry. The causative virus is an alphaherpesvirus that causes immunosuppression and predisposes poultry to other pathogens.  Although the MD is more common in laying, the incidence of the disease is also increasing in broilers. Due to the increasing rate of infection with the marker virus in broiler chickens, this study aimed to investigate the occurrence of MD in broiler poultry farms in Semnan, Iran. The feather follicle epithelium and spleen tissues were collected randomly from 15 broilers flocks at 6-10 weeks old in Semnan slaughterhouse and were subjected to polymerase chain reaction by amplifying the meq gene. The results of this study showed of 15 flocks, two (13.6%) had a positive reaction. There was no evidence of macroscopic lesions among the studied flocks. Considering the infection of 13.6% of the studied flocks, without any macroscopic complications, it seems the MD virus is circulating in broilers and could transmit to the other birds. It is indicated that the current national vaccination has not stopped the disease in commercial chickens. Due to the immunosuppressive properties of the virus, it is considered that the MD virus, along with other immunosuppressive agents such as adenoviruses, has an essential role in the development of immunosuppression syndrome in broilers in Iran, and to reduce the economic losses caused by this disease, effective prophylactic measures should be considered by the country's health officials.