Effect of route of infection and vaccination status on detection of Marek's disease virus from blood or spleen by polymerase chain reaction

Polymerase chain reaction (PCR) has recently emerged as an additional tool for the diagnosis of Marek's disease (MD). The effect of route of infection and vaccination status on detection of Marek's disease virus (MDV) in blood or spleen of infected commercial broiler chickens by serotype-specific PCR was investigated. Commercial vaccinated and unvaccinated broilers were placed in isolators and challenged or not challenged with virulent MDV at day 3 of age either by intra-peritoneal injection or by inhalation of feather dust. On days 7, 14, 21, 28 and 35 post infection (PI), 50 birds were weighed, blood sampled and euthanased for various measurements including MDV serotype 1 (MDV-l) PCR of spleen tissue and peripheral blood lymphocytes (PBL). Spleen and PBL were found to provide similar sensitivity of detection of MDV with a slight advantage in favour of spleen. Infection of birds by inhalation of infective feather dust resulted in a slightly later but more complete appearance of MDV in challenged birds. Vaccination delayed the detection of MDV by approximately 2 weeks and it did not protect against the lower live weight observed at day 35 PI in infected birds.