Marek's disease in broiler chickens: effect of route of infection and herpesvirus of turkey-vaccination status on detection of virus from blood or spleen by polymerase chain reaction, and on weights of birds, bursa and spleen

The polymerase chain reaction (PCR) has recently emerged as an additional t ool for the monitoring and diagnosis of Marek's disease. We investigated a number of factors that may influence the interpretation of PCR results in c ommercial broiler chickens including the effects of route of infection and herpesvirus of turkeys (HVT)-vaccination status. We also investigated the s uitability of peripheral blood lymphocytes ( PBL) and spleen as tissues for Marek's disease virus (MDV) detection. HVT-vaccinated and unvaccinated com mercial broiler chickens were challenged or not challenged with virulent MD V either by intraperitoneal injection or inhalation of feather dust contain ing the virus. Blood and spleen samples were collected at weekly intervals to day 35 post-infection for PCR of spleen or PBL. Live weight and lymphoid organ weights were also measured. Spleen and PBL were found to provide sim ilar sensitivity of detection of MDV with a small advantage in favour of sp leen. In terms of the timing of detection of MDV, intraperitoneal challenge broadly mimicked natural challenge via inhalation, although infection of b irds by inhalation of infective feather dust resulted in slightly later but more complete detection of MDV in challenged birds. Vaccination with HVT d elayed the detection of MDV by approximately 10 to 14 days and did not prot ect against the reduced growth observed in challenged chickens at day 35 po st-challenge.