Synonyms: Diplospora lieberkuhni (Labbe, 1894) Grasse, 1953; Hyaloklossia lieberkuhni (Labbe, 1894) Labbe, 1896; Klossia lieberkuhni Labbe, 1894; Isospora lieberkuehni (Labbe, 1894) Laveran and Mesnil, 1902.

Type host: Pelophylax esculenta (L., 1758), Pool frog.

Other hosts: Lithobates pipiens (Schreber, 1782), Northern leopard frog; Pelophylax ridibunda (Pallas, 1771), Marsh frog; Rana temporaria L., 1758, Grass frog; Bombina variegata (L., 1758), Yellowbelly toad.

Type locality: EUROPE: France.

Geographic distribution: EUROPE: Bulgaria, Czech Republic, France, Poland; NORTH AMERICA: U.S.A.: Wisconsin.

Description of oocyst: Oocyst shape in situ: asymmetrically ellipsoidal; number of walls: 1; wall thickness: "very thin"; wall characteristics: transparent, elastic, and fragile; L x W: 35-45 x 20-25; L/W ratio: not given; M: absent; OR: absent; PG: absent. Distinctive features of oocyst: intracellular development and sporulation.

Description of sporocysts and sporozoite: Sporocyst shape: broadly spindle-shaped to ellipsoidal; L x W: 25-30 x 14-16; L/W ratio: not given; SB: absent; SSB: absent; PSB: absent; SR: present; SR characteristics: spheroidal to subspheroidal cluster of irregular granules, 9.5-17 x 7-12; SZ: elongate, banana-shaped, 17-21 x 3-4 with a small, round RB at their rounded end (line drawing). Distinctive features of sporocysts: very thin wall.

Prevalence: Usually not stated, but 1 of 137 (<1%) L. pipiens in Wisconsin (Levine & Nye, 1977); 2 of >2000 (<0.1%) P. esculenta in Poland (Kazubski & Grabda-Kazubski, 1973); 4 of 16 (25%) frogs during April and May and 0 of 18 (0%) frogs in July in the Czeck Republick (Modrý et al., 2001) and Vojtková (1976) not stated; Laveran and Mesnil (1902b) in France and Nöeller (1923) in Germany both reported a high degree of infection in young P. esculenta.

Sporulation: Endogenous, within the tubular epithelial cells of the kidney.

Prepatent and patent periods: Unknown, but oocysts may rupture intracellularly releasing sporocysts into the renal tubes.

Site of infection: Epithelium of renal tubes.

Endogenous development: According to Laveran and Mesnil (1902b), within only 48 h after ingesting oocysts, the parasite produces an intense infection in various organs of the body with both meronts and gamonts. Nöller (1923) found sporozoites in the spleen of 16 day old tadpoles after he had infected them with sporocysts. Merogony occurred in the spring in the glomerular epithelium of the kidneys of young frogs, but did not develop to gamonts until the summer. Merozoites were short and crescent-shaped with a central N. Gamonts also developed in glomerular epithelial cells. Macrogamonts were elongate ovoidal to ellipsoidal bodies with a large N and a granular cytoplasm. Mature microgamonts had peripherally arranged N and each microgamete had 2 flagella. Levine and Nye (1977) found from 1–12 merozoites per host cell in the cytoplasm of kidney tubule epithelial cells where they completely destroyed the cytoplasm, but left the N intact although sometimes shrunken. The merozoites they saw were elongated and slightly curved, ~6–7 long, with a central or subcentral spherical or squarish N, ~1, and similar to those described by Nöller (1923).

Pathology: Produces marked pathological changes in the kidneys where they form large, whitish cyst-like structures filled with granular contents consisting of mostly immature oocysts (Kazubski & Grabda-Kazubski, 1973).

Materials deposited: SSU rRNA sequences in GenBank (AF298623).

Remarks: Lieberkühn (1854) was the first to find this renal coccidium in P. esculenta in France. Later, Labbé (1894b) described it under the name Klossia lieberkühni and two years later, in 1896, after re-evaluating its status, he erected the genus Hyaloklossia to accommodate this species. Later authors (Laveran & Mesnil 1902b; Minchin 1903) placed H. leiberküehni into the genus Diplospora Labbé 1893; still others (Nöller 1923; Doflein & Reichenow 1953) placed it into the genus Isospora (Schneider 1881). Recognizing that the genus Isospora is now known to be polyphyletic, Modrý et al. (2001) collected I.” lieberküehni from P. esculenta in the Czech Republic, extracted DNA, and amplified and sequenced the SSU rRNA gene. Using various phylogenetic analyses to examine the phylogenetic position of this enigmatic organism to species in both the Eimeriidae (Isospora, Eimeria, Cyclospora) and the Sarcocystidae (Sarcocystis, Toxoplasma, Hammondia, Neospora, and others) they concluded that, the unique combination of morphological, biological and phylogenetic features was sufficient to re-erect and emend the oldest available synonym, Hyaloklossia with H. liberküehni as the type species. Nöller (1923) believed that the endogenous stages reported in organs other than the kidneys by Laveran and Mesnil (1902b) were actually Lankesterella minima, and that the endogenous stages of H. (=I.) lieberküehni are limited to the kidney. Nöller (1923) also gave the details of the life history noting that oocysts deposited in the water were swallowed by tadpoles in which the SZ make their way to the glomeruli of the kidneys, where merogony takes place in the epithelial cells. Resulting merozoites then invade the tubule epithelium, which was found heavily infected with other meronts in young frogs during late April and early May. Several weeks later, macro- and microgamonts were found in tubule cells where the oocysts formed (Wenyon 1926). Nöller (1923) said microgametes were biflagellate. Levine and Nye (1977) reported the infection in 1 L. pipiens from Wisconsin, USA, as a new host and geographic record based solely on merozoites seen in the kidney tubule epithelial cells. We feel that Levine and Nye (1977) had no justification in identifying H. lieberküehni based on merozoites seen in the kidney tubules and their report may represent an undescribed species of apicomplexan from the northern leopard frog. Pellérdy (1974, p. 725) indicated that this species, along with I.mesnili, E. ranarum and E. salamandrae, are all intranuclear parasites.