Myofibers were necrotic and fragmented and have plump oval nuclei with one or two prominent nucleoli. Macrophages contained clusters of lightly basophilic organisms with a small clear halo. These organisms were tissue gram stain and acid-fast positive. They were not observed in other organ systems including kidney, brain, lung, liver, heart, or intestinal tract. Mononuclear inflammation and muscle necrosis and fragmentation.
Arrows point to intracytoplasmic organisms in macrophages.
Acid fast stain. Acid fast organisms within macrophages. These electron micrographs are actually from a microsporidian infection in a budgie and are used here for illustration purposes only. They enter the host cell through mechanical forces of an extruded polar filament from the sporoplasm. The sporoplasm then actively migrates through the host tissue.