Apoptosis as a cause of death in chicken embryos inoculated with Newcastle disease virus.

Eleven-day-old chicken embryos were inoculated by the allantoic route with the GB strain of Newcastle disease virus (NDV). At 0, 24, 36 and 42 h post-inoculation (p.i.), the brain and heart tissues were harvested for DNA extraction, and the thymus and the brain were fixed and processed for light and electron microscopy. At 42 h p.i., most of the embryos had died; however, no histopathological changes could be seen in the embryos at any stage of infection. DNA extracted from the brain cells started showing fragmentation at 24 h p.i., and from the heart muscle cells at 36 h p.i. Electron microscopy of the brain and thymus showed condensation of the nuclear chromatin, apoptotic bodies, various forms of crescent formation and some evidence of necrosis. Fragmentation of cellular DNA, crescent formation and apoptotic bodies are the typical signs of cells undergoing apoptosis. We suggest that apoptosis of the heart and brain is probably a cause of death of chicken embryos in acute Newcastle disease infection.