Cryptosporidium sp. oocysts from a dog (arrows) a Trichuris vulpis egg is visible out of focus on the right. Transmission is via ingestion of the oocyst, which is immediately infective when passed and contains four sporozoites. Oocysts are viable for months unless exposed to extreme temperatures (below freezing or greater than 65°C) or desiccation.
Cystoisospora felis and Cystoisospora rivolta
Two species of coccidia in cats include Cystoisospora felis (larger of the two, ovoid in shape, sizes range from 38-51 μm by 27-29 μm, oocyst wall is smooth with no micropyle, sporulation time is 72 hrs) and Cystoisospora rivolta (smaller of the two, ellipsoidal in shape, sizes range from 21-28 μm by 18-23 μm, micropyle is present at narrower end, sporulation time is 4 days). Both species are usually non-pathogenic.
Eimeria bukidnonensis and Eimeria auburnensis
Two Eimeria species of cattle. Eimeria bukidnonensis (pear-shaped to oval, yellowish brown to dark brown in color, average size of 44 μm by 31 μm, micropyle present at narrower end, sporulation time 72-96 hrs) is at the top of field of view and Eimeria auburnensis (one of the most common coccidia in cattle, oocyst shape varies from ellipsoidal to tapering, sizes range from 32-46 μm by 20-25 μm, sporulation time is 48-72 hrs) is at the bottom of the field of view.
The major pathogenic coccidium of cattle, oocysts are spherical to ellipsoidal in shape, with sizes ranging from 15-22 μm by 13-18 μm. The wall of the oocyst is thin and smooth, being clear to pale-yellow in color. There is no visible micropyle and sporulation occurs in 23-24 hours. Disease is characterized by hemorrhagic diarrhea.
Neospora caninum or Hammondia heydorni oocyst
Oocysts, both sporulated and nonsporulated, found in canine feces, measuring 11 μm in diameter, viewed at 1000X. Oocysts of Neospora caninum and Hammondia heydorni are almost identical in morphology, with Hammondia heydorni sometimes described as approximately 1 μm larger on average. Oocysts of Neospora caninum are only rarely found in canine fecal preparations.
Histologic section of bovine dermis showing 'pearl' cysts. Cattle serve as an intermediate host for this ampicomplexan, which forms spherical bradyzoite packed cysts which may be found in the dermis, subcutaneous tissues, fascia, and mucosa of affected animals. Visible cysts in the scleral conjunctiva are the most characteristic clinical sign of infection.
Besnoitia darlingi tissue cysts in the dermis, subcutaneous tissues, and fascia of an opossum. Cats have been shown to be the definitive host of Besnoitia darlingi and opossums (Didelphis virginiana) the intermediate host. Opossums acquire infection through the ingestion of infected tissues or water contaminated with oocysts from cat feces.
Hemosporidians, Malarias, and Hepatozoon
Characteristic "onion skin" cyst of Hepatozoon americanum in a histologic muscle preparation from an infected dog. These cysts are associated with parasite schizogony within leukocytes situated between striated muscle fibers, and are pathognomonic for infection with this parasite. Here, the parasite has invaded the host cell and induced cyst formation, but has not yet begun to undergo schizogony