Evidence for Marek's disease in turkeys in Germany: detection of MDV-1 using the polymerase chain reaction

Since 1994 tumorous lesions have been monitored in turkeys on three farms in Germany. On one of these farms, chickens also had tumorous lesions. Affected turkeys were retarded in growth, apathic, pale and almost unable to move. The older the animals got, the more indistinct the clinical signs became. Mortality started at an age of 5 weeks and reached between 20% and 60% by the end of the fattening period of about 20 weeks. The aetiological differential diagnosis includes reticuloendotheliosis (RE), lymphoproliferative disease (LPD), lymphoid leukosis (LL) and Marek's disease (MD). Repeated serological examinations did not establish the presence of antibodies against REV, LLV or MDV-1. Cloacal swabs were negative for LL P27 antigen in ELISA. Solid tumors of various sizes as well as diffuse infiltrations were predominantly seen in the liver, spleen and kidney. Pleomorphic cell infiltration was rarely noted in the plexus brachialis and nervus ischiaticus. Herpesvirus of turkeys (HVT) was the only virus isolated from buffy coat cells derived from affected turkeys in chicken embryo kidney cell (CEK) and chicken embryo fibroblast (CEF) cultures. Use of polymerase chain reaction (PCR) for the amplification of the 132 bp repeat region provided evidence for the presence of MDV-1 DNA in tumor tissue from several diseased turkeys. No evidence was found for the presence of REV.