Synonyms: Haemoproteus anatis, Haemoproteus hermani.
Hosts: Domestic duck, domestic white Chinese goose, and over 23 species of wild ducks, geese and swans, including the Canada goose, whistling swan, wood duck, pintail, green-winged teal, Australian teal, blue-winged teal, mallard, black duck, white-winged duck, cotton teal, Australian sheldrake, wattle duck, shoveller, Baer's pochard, ring-necked duck, white-eyed duck, rufous-crested duck, baldpate, common goldeneye, surf scoter, old squaw and common merganser (Levine and Hanson, 1953; Herman, 1954; Fallis and Wood, 1957).
Location: The gametocytes are in the erythrocytes. Schizogony occurs in the endothelial cells of the blood vessels.
Geographic Distribution: Worldwide.
Prevalence: Common. This species is a parasite of wild waterfowl which may infect domestic ducks in heavily endemic regions.
Morphology: Only the sexual stages are found in the red blood cells. Except early in an infection, young stages are absent or rare. The mature macrogametes and microgametocytes are elongate and sausage-shaped, partially (or sometimes completely) encircling the host cell nucleus, often displacing it. There is frequently a narrow band of cytoplasm between the parasite and the host cell nucleus, Free macrogametes and microgametocytes may occasionally be found; these are usually round. The macrogametes and microgametocytes contain a few to 30 or more (usually 12 to 24) pigment granules which are usually coarse and round and tend to be grouped at the ends of the cell. The host cell is not enlarged.
When stained with a Romanowsky stain, the cytoplasm of the microgametocytes is pale blue or almost colorless and their nuclei are pale pink and diffuse, while the cytoplasm of the macrogametes is darker blue and their nuclei are compact and dark pink or red.
Life Cycle: The vector of H. nettionis was first discovered by Fallis and Wood (1957). It is the biting midge, Culicoides. The prepatent period in experimentally infected birds is 14 to 21 days. Schizogony has not been described, and the details of sporogony in the midge are still to be worked out. Fallis and Wood found ookinetes in the midge stomach 36 hours after ingestion; they found structures which they regarded as oocysts on the stomach wall, and other structures which they regarded as sporozoites in the salivary glands.
Pathogenesis: H. nettionis is only slightly if at all pathogenic.