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*Cause disease in animals and are important zoonoses
*Cause disease in animals and are important zoonoses
*10 species of which ''Yersinia pestis, Yersinia pseudotuberculosis amd Yersinia enterocolitica'' are pathogenic to animals and humnans
*Rodents provide a reservoir of ''Yersinia pestis'', which is the cause of human plague; fleas transmit the infection to other animals and humans
*''Yersinia pseudotuberculosis and enterocolitica'' reside in the intestine of domestic and wild animals and birds
*Birds may cause mechanical transfer of the organisms
===Characteristics===
===Characteristics===
*Enterobacteria, but grow more slowly and at lower temperatures than other enterobacteria
*Enterobacteria, but grow more slowly and at lower temperatures than other enterobacteria
*Gram negative, non-spore forming, facultative anaerobes - rods or colibacilli
*Non-lactose fermentors
*Non-lactose fermentors
*Facuiltative intracellular pathogens
*Facultative intracellular pathogens
*Show bipolar staining in Giemsa-stained smears from animal tissue
*Pathogenic strains identified by serotyping and biotyping
===Pathogenesis===
===Pathogenesis===
*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
*The bacteria destroy macrophages in lymph nodes, liver and spleen, causing septicaemia
===Clnical infections===
===Clnical infections===