Incidence of Marek’s Disease in Vaccinated Flocks

A study was undertaken to assess the incidence of Marek’s Disease (MD) in vaccinated flocks. Blood, organ and feather follicle samples were collected from fifteen commercial layer farms in which Marek’s Disease outbreak was occurred even after vaccination with monovalent and bivalent vaccines. Blood samples were screened for serotype 1 specific132bp repeats and lymphocytes from corresponding positive samples for 132 bp repeats alone used for virus isolation. Organ samples were processed by routine procedure for isolation of virus and treated with antibiotics and filtered (0.45) before inoculation. Feather follicles were soaked in SPGA/EDTA buffer and extract used for isolation. 11 days old duck embryos were used to prepare Duck embryo fibroblast culture (DEF). Three passages were carried out in DEF and presence of positive serotype 1 virus was confirmed by PCR for 132bp repeats. Subsequently the isolates were adopted in Chicken Embryo Fibroblast (CEF) culture and produced typical MD plaques. There were three isolates of serotype 1 MD virus recovered from fifteen (20%) field cases. The finding suggests that the Marek’s Disease occurrence is prevalent in vaccinated flocks.