Difference between revisions of "Piroplasmida"

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==''Theileria''==
 
==''Theileria''==
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[[Image:Theileria parva life cycle.jpg|thumb|right|150px|''Theileria parva'' Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC]]
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*Main species of veterinary importance is ''Theileria parva''
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**Causes '''East Coast Fever'''
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***Severe, proliferative lymphatic disease of cattle
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***Central and Eastern Africa
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***Transmitted by [[Suborder: Metastigmata, ticks#Ticks of Veterinary Importance|''Rhipicephalus appendiculatus'']]
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***[[Suborder: Metastigmata, ticks#Disease Transmission|Trans-stadial]] transmission
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*Other ''Theileria'' species causes production losses in cattle and sheep in the Middle East, Mediterranean and in Northern Africa
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'''Life Cycle'''
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'''Pathogenesis'''
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'''Diagnosis'''
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'''Control'''
  
 
==''Cytauxzoon felis''==
 
==''Cytauxzoon felis''==

Revision as of 16:17, 22 November 2008


Infectious agents and parasitesWikiBugs Banner.png
PARASITES
PROTOZOA



Babesia

Theileria

Theileria parva Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC
  • Main species of veterinary importance is Theileria parva
  • Other Theileria species causes production losses in cattle and sheep in the Middle East, Mediterranean and in Northern Africa

Life Cycle

Pathogenesis

Diagnosis

Control

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

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