Difference between revisions of "Piroplasmida"
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− | ==Cytauxzoon felis== | + | ==''Babesia''== |
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+ | * May cause haemolysis and [[General Pathology - Pigmentation and Calcification#Haemoglobin|haemoglobin pigmentation]]. | ||
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+ | ==''Theileria''== | ||
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+ | ==''Cytauxzoon felis''== | ||
*Cytauxzoon is classified in the order ''Piroplasmida'' and family ''Theileriidae'' | *Cytauxzoon is classified in the order ''Piroplasmida'' and family ''Theileriidae'' |
Revision as of 20:05, 18 November 2008
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Babesia
- May cause haemolysis and haemoglobin pigmentation.
Theileria
Cytauxzoon felis
- Cytauxzoon is classified in the order Piroplasmida and family Theileriidae
- This family has both an erythrocytic and a tissue (leukocytic) phase
- The Babesiidae, a related family, is characterized by having a primarily erythrocytic phase in the mammalian host
- Its morphological features are indistinguishable from the erythrocytic form of Cytauxzoon
- Cytauxzoon felis, B. equi, and B. rodhaini have been linked to both the babesias and theilerias by RNA gene sequence analysis
- It has been suggested that these organisms be reclassified within a separate family
Life Cycle
- Large schizonts of C. felis develop in macrophages
- In Theileria the exoerythrocytic stage occurs primarily within lymphocytes
- In C. felis, schizonts develop within mononuclear phagocytes, initially as indistinct vesicular structures and later as large, distinct nucleated schizonts that actively undergo division by true schizogony and binary fission
- Later in the course of the disease, schizonts develop buds (merozoites) that separate and eventually fill the entire host cell
- Each schizont may contain numerous merozoites
- Ultrastructurally, schizonts lack a parasitophorous vacuole, and individual merozoites possess rhoptries
- The host cell ruptures, releasing merozoites into the tissue fluid and blood
- Merozoites are then believed to enter erythrocytes to form the intraerythrocytic stage
- Merozoites appear in macrophages one to three days before they are observed in erythrocytes
Pathogenicity
- Ticks are implicated as the natural vector for Cytauxzoon
- Most cases of infection have been associated with the presence of these parasites on the hosts
- Experimentally, Dermacentor variabilis can transmit the organism from bobcats to domestic cats. In a white tiger that developed a natural, fatal infection in Florida, two female Lone Star ticks (Amblyomma americanum) were present on the inguinal skin.
- Clinically, the disease in cats is characterized by fever, depression, dyspnea, anorexia, lymphadenopathy, anaemia, and icterus leading to death in three to six days
- Gross findings include pale or icteric mucous membranes, petechiae and ecchymoses in the lung, heart, lymph nodes and on mucous membranes, splenomegaly, lymphadenomegaly, and hydropericardium
- Microscopically, numerous large schizonts are present within the cytoplasm of endothelial-associated macrophages
- Infected macrophages become markedly enlarged (up to 75μm) and may occlude the lumens of numerous vessels of many tissues, especially the lungs
- Minimal inflammatory reaction is present in tissues
Diagnosis
- Merozoites within erythrocytes, best seen on peripheral blood or tissue impressions, are variable in morphology and can occur as round, oval, or signet ring-shaped bodies
- Are 1-5 micrometers in diameter
- Small, peripherally placed basophilic nucleus
- Organisms that must be distinguished from the intraerythrocytic phase of C. felis include Babesia and Hemobartonella
- The blood stage may appear similar to the ring forms of Hemobartonella and to the piriforms of Babesia
- Unlike Cytauxzoon, babesiosis and hemobartonellosis do not have a tissue stage of infection
- Differential diagnosis for the tissue phase of cytauxzoonosis includes other small (less than 5 μm), intrahistiocytic organisms such as Toxoplasma, Leishmania and Histoplasma