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*Cause disease in animals and are important zoonoses
 
*Cause disease in animals and are important zoonoses
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*10 species of which ''Yersinia pestis, Yersinia pseudotuberculosis amd Yersinia enterocolitica'' are pathogenic to animals and humnans
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*Rodents provide a reservoir of ''Yersinia pestis'', which is the cause of human plague; fleas transmit the infection to other animals and humans
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*''Yersinia pseudotuberculosis and enterocolitica'' reside in the intestine of domestic and wild animals and birds
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*Birds may cause mechanical transfer of the organisms
    
===Characteristics===
 
===Characteristics===
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*Enterobacteria, but grow more slowly and at lower temperatures than other enterobacteria
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*Enterobacteria, but grow more slowly and at lower temperatures than other enterobacteria  
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*Gram negative, non-spore forming, facultative anaerobes - rods or colibacilli
 
*Non-lactose fermentors
 
*Non-lactose fermentors
*Facuiltative intracellular pathogens
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*Facultative intracellular pathogens
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*Show bipolar staining in Giemsa-stained smears from animal tissue
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*Pathogenic strains identified by serotyping and biotyping
    
===Pathogenesis===
 
===Pathogenesis===
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*Survive in phagolysosomes and do not interfere with degranulation or lysosomal fusion
 
*Survive in phagolysosomes and do not interfere with degranulation or lysosomal fusion
 
*Resistant to macrophage killing mechanisms
 
*Resistant to macrophage killing mechanisms
*The bacteria destroy the macrophages in lymph nodes, liver and spleen, causing septicaemia
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*The bacteria destroy macrophages in lymph nodes, liver and spleen, causing septicaemia
    
===Clnical infections===
 
===Clnical infections===
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