Pre-erythrocytic development and associated host responses to Haemoproteus meleagridis (Haemosporina: Haemoproteidae) in experimentally infected domestic turkeys.

Two generations of pre-erythrocytic schizogony occurred in skeletal and cardiac muscle of domestic turkeys infected with sporozoites of Haemoproteus meleagridis. First generation schizonts reached maturity approximately five days post-inoculation (DPI) and developed in capillary endothelial cells and myofibroblasts. The schizonts ranged from 12 to 20 microns in diameter and produced long (5-6 microns), slender merozoites. Early second generation schizonts were first detected in capillary endothelial cells between 5 and 8 DPI. They were cylindrical and ranged in size from 5 to 8 microns in diameter and up to 28 microns in length. Second generation schizonts which reached maturity by 17 DPI were surrounded by a thick, hyaline wall and were packed with numerous spherical merozoites less than 1 micron in diameter. Mature megaloschizonts were fusiform, ranged from 30 to 113 microns in diameter, and extended as much as 465 microns along the long axis of muscle fibers. Merozoites developed as buds from cytomeres that formed between 8 and 14 DPI. Infected turkeys developed a moderate to severe myositis within 5 DPI and were lame in one or both legs. The myositis was associated with the necrosis of scattered groups of muscle fibers. Muscle fibers surrounding mature megaloschizonts were swollen and hyaline. Megaloschizonts were surrounded occasionally by fibroblasts and infiltrates of mononuclear cells. The morphology and site of development of mature megaloschizonts of Haemoproteus meleagridis are contrasted with those of other avian haemosporidians.