Graft-versus-host disease (GVHD) is a common side effect of an allogeneic bone marrow transplant. An allogeneic transplant uses blood cells from a family member, unrelated donor or cord blood unit.
Nearly all vertebrate animals host one or more species of the protozoan parasites that produce the infection referred to as coccidiiasis or coccidiosis. Thousands of coccidian species of herbivorous, omnivorous, and carnivorous animals have been described, and many more exist that remain unnamed.
The disease is caused by a protozoan, a relative of coccidia, that is found in cecal worms of poultry and other fowl. The bird is infected by the cecal worm and is then infected by the blackhead organism Histomonas meleagridis.