Haematological and histological findings in experimental newcastle disease

Abstract

To obtain more information about pathogenesis of haemorrhages in Newcastle disease, blood cells counts with special emphasis on thrombocytes were performed in 25 specific pathogen-free chickens experimentally infected by ocular instillation of 106 embryo-lethal doses 50% of a velogenic viscerotropic strain of Newcastle disease virus (Chimalhuacan strain); five control chickens 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 haematopoietic islands was noted at 48 hpi. At 60 hpi, an increase in heterophil and a decrease in monocyte and lymphocyte counts was observed; thromboblasts showed basophilia, nuclear and cytoplasmic vacuolation. During the same period, 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 reduction at 72 h post infection (hpi) of thrombocyte counts and multifocal necrosis of bone marrow cells was observed. Our results suggested that thrombocytopenia was the end result of a direct viral damage to bone marrow precursor cells.