Difference between revisions of "Piroplasmida"

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==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 - WikiBlood|macrophages]]
 
**In Theileria the exoerythrocytic stage occurs primarily within [[Lymphocytes - WikiBlood|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 - WikiBlood|macrophages]] one to three days before they are observed in [[Erythrocytes - WikiBlood|erythrocytes]]
 
 
'''Pathogenicity'''
 
*[[Suborder: Metastigmata, ticks|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 [[Lungs - Anatomy & Physiology|lung]], [[Heart - Anatomy & Physiology|heart]], [[Lymph Nodes - Anatomy & Physiology|lymph nodes]] and on mucous membranes, splenomegaly, lymphadenomegaly, and hydropericardium
 
 
*Microscopically, numerous large schizonts are present within the cytoplasm of endothelial-associated [[Macrophages - WikiBlood|macrophages]]
 
**Infected macrophages become markedly enlarged (up to 75μm) and may occlude the lumens of numerous vessels of many tissues, especially the [[Lungs - Anatomy & Physiology|lungs]]
 
**Minimal inflammatory reaction is present in tissues
 
 
 
'''Diagnosis'''
 
*Merozoites within [[Erythrocytes - WikiBlood|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''
 

Latest revision as of 22:38, 9 April 2010