Haematological and histological findings in experimental Newcastle disease

To obtain more information about pathogenesis of haemorrhages in Newcastle disease, blood cells counts with special emphasis on thrombocytes were perf ormed in 25 specific pathogen-free chickens experimentally infected by ocul ar instillation of 10(6) embryo-lethal doses 50% of a velogenic viscerotrop ic strain of Newcastle disease virus (Chimalhuacan strain); five control ch ickens were included. Histological evaluation of the bone marrow, the brain , the kidneys, the lungs and the proventriculus was carried out. Birds were killed at 24 h post infection, followed by 12 h intervals. Whole blood and tissue samples were collected. In the bone marrow early necrosis of haemat opoietic islands was noted at 48 hpi. At 60 hpi, an increase in heterophil and a decrease in monocyte and lymphocyte counts was observed; thromboblast s showed basophilia, nuclear and cytoplasmic vacuolation. During the same p eriod, swelling and vacuolation of capillary endothelial cells were evident , mainly in the lungs. We consider thrombocytopenia and endothelial damage to be the main causes of haemorrhages in this animal model. A significant r eduction at 72 h post infection (hpi) of thrombocyte counts and multifocal necrosis of bone marrow cells was observed. Our results suggested that thro mbocytopenia was the end result of a direct viral damage to bone marrow pre cursor cells.