Synonyms: Monocystis stiedae, Coccidium oviforme, Coccidium cuniculi.
Hosts: Domestic rabbit, European hare (Lepus europaeus), varying hare (L. americanus), black-tailed jack rabbit (L. californicus), alpine hare (L. timidus), L. variabilis, cottontails (Sylvilagus floridanus, S. nuttalli).
Location: Liver. The coccidia are found in the bile duct epithelial cells.
Geographic Distribution: Worldwide.
Prevalence: This is the most common and most important coccidium of domestic rabbits. It also occurs in hares (Lepus), but is less common in cottontails than other species.
Morphology: The oocysts are ovoid, sometimes ellipsoidal, with a flat micropylar end, and measure 28 to 40 by 16 to 25 u with a mean of 37 by 21 u. The oocyst wall is smooth and salmon-colored. A micropyle is present. An oocyst polar granule and oocyst residuum are absent. The sporocysts are elongate ovoid, 18 to 10 u, with a Stieda body. A sporocyst residuum is present. The sporulation time is 3 days.
Life Cycle: The life cycle of this species has been studied by a number of workers (see Becker, 1934, for a review). The sporulated oocysts excyst in the small intestine. The sporozoites penetrate the intestinal mucosa, enter the hepatic portal system, and pass to the liver. Here they enter the epithelial cells of the bile ducts. The liver parenchyma cells are only rarely invaded. Development takes place above the host cell nucleus.
Each sporozoite rounds up and becomes a schizont which produces 6 to 30 or more (usually 8 to 16) merozoites which measure about 8 to 10 by 1.5 to 2.0 u. The number of asexual generations is not known. Later, some merozoites become microgametocytes which produce large numbers of comma-shaped, biflagellate microgametes, while others become macrogametes. These are fertilized, lay down an oocyst wall, break out of their host cell, pass into the intestine with the bile and thence out of the body. The prepatent period is 18 days.
Pathogenesis: In mild cases of liver coccidiosis there may be no signs, but in more severe ones the animals lose their appetites and grow thin. There may be diarrhea, and the mucous membranes may be icteric. The disease is more severe in young animals than in old. It may be chronic, or death may occur in 21 to 30 days.
Some of the symptoms are due to interference with liver function. The liver may become markedly enlarged, and white circular nodules or elongated cords appear in it. At first they are sharply circumscribed, but later they tend to coalesce. They are enormously enlarged bile ducts filled with the developing parasites. There is tremendous hyperplasia of the bile duct epithelial cells. Instead of forming a simple, narrow tube, the epithelium is thrown into great, arborescent folds, and each cell contains a parasite.
Dunlap, Dickson and Johnson (1959) found that infection with E. stiedae increased the serum B- and Y-globulin and B-lipoprotein and decreased the A-lipoprotein.