Morphology

a. S. bovicanis (S. cruzi)

• Meronts found in endothelial cell are quite small, measuring 2-8 µm in diameter.
• Bradyzoite cyst can be large and visible to naked eye as whitish streaks running in direction at muscle fibers.
• Cyst wall is thin and smooth and has small number of flattened protensions 0.3-0.6 µm long, without fibrils.
• Sporulated oocyst are fully sporulated and dumb-bell shaped, if passed in feces, with thin oocyst wall sunken between two sporocyst, without a micropyle, polar granule, or oocyst residuum.
• Sporocyst are ellipsoidal, 14.3-17.4 x 8.7-13.3 µm , smooth colorless without a steida body but with a residuum and each has four sporozoites.

b. S. bovifelis

• First generation meronts contains more than 100 tachyzoites and measures 37×22 µm.
• Second generation meronts, usually measure 14×6.5 µm and contain upto 35 tachyzoites.
• Sporocyst are upto 8 mm long with a straited wall, 7 µm thick and may be visible to naked eye.
• Oocyst are smooth, colorless and contain two sporocyst. Each sporocyst contain four sporozoites.
• Sporocyst are dumb-bell shaped in appearance with no micropyle, polar granule or oocyst residuum.
• Sporocyst are ellipsoidal without a steida body but with a residuum.

c. S.ovicanis

• Fires-generation meronts are found in endothelial cells and contain 120-280 merozoites.
• Tissue cyst are microscopic in size (500×60-100 µm) and are found in skeletal and cardiac muscle.
• Wall of cyst appears thick and radially straited with long palisade-like protrusions without fibrils.
• Oocyst are sporulated when passed in faeces and contain two sporocyst, Each sporocyst contain four sporozoites.

d.  S. ovifelis

• Syn : tenella, S. gigantea, S. medisiforms, Isospora bigemina
• Meronts are found in endothelial cells and are quite small measuring 2-8 µm in diameter.
• Bradyzoite cyst measures about 1.5 cm x 0.2-5mm.
• Cyst wall has numerous cauliflowers like protrusions, each containing numerous fibrils.
• Parasitized host cell is enclosed in connective tissue forming secondary cyst wall.
• Sporulated sporocyst are ellipsoidal.