Wright's stain, 500x

Leucocytozoon sp. and Hemoproteus sp.

This blood smear contains hemoparasites found in a Great Horned Owl. Two common parasites are Leucocytozoon sp. (black arrow) and Hemoproteus sp. (red arrow). The black arrow at the top of the image illustrates a Leucocytozoon sp. gametocyte and the lower arrow illustrates a Leucocytozoon sp. macrogametocyte. This parasite is usually intracellular, living within leukocytes or erythrocytes. Despite this parasite’s name, there is some debate as to which cell type is infected. Leucocytozoon sp. is transmitted by blackflies and can be found in many avian species. The pathogenicity of the parasite is generally low, but some species are more susceptible to disease, such as water fowl, turkeys, and young birds of prey. The diagnosis requires examination of a blood smear.

Hemoproteus sp. (red arrow: Hemoproteus sp. gametocyte) is found frequently in many avian species and is distributed worldwide. This organism is transmitted by blood-sucking insects which can act as intermediate hosts. The parasite is found mostly in erythrocytes and is often seen encircling the nucleus. It has a granular content often accompanied by some black pigment. The low pathogenicity of this organism is such that infected birds rarely show signs of illness, except for highly susceptible species such as pigeons and quails.