Amelioration of Marek's disease and absence of vaccine protection in immunologically deficient chickens

MAREK'S disease (MD) is a lymphoproliferative disease of chickens which is generally considered to be neoplastic¹. It is probably the most commonly occurring neoplasm of any animal and until recently it caused extensive economic loss, estimated to be in excess of 150 million dollars annually, to the poultry industry². Several viral vaccines which will effectively prevent the disease have been developed³ and the most extensively used is a herpesvirus isolated from turkeys (HVT)⁴, which will prevent the disease in laboratory and field trials^5,6.