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===Pathogenesis===
 
===Pathogenesis===
   −
*Faemcal-oral transmission
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*Faecal-oral transmission
 
*Comparitively large dose required for infection due to gastric acid, normal intestinal flora and local immunity
 
*Comparitively large dose required for infection due to gastric acid, normal intestinal flora and local immunity
 
*Enterocolitis:
 
*Enterocolitis:
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**Degeneration of microvilli
 
**Degeneration of microvilli
 
*Systemic disease:
 
*Systemic disease:
**Bacteria invade the body
   
**Bacteria internalised by intestinal epithelial cells  
 
**Bacteria internalised by intestinal epithelial cells  
 
**Stimulate immune response on reaching the lamina propria
 
**Stimulate immune response on reaching the lamina propria
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**Bacteria either destroyed by the phagocytic cells or survive and multiply in the cells to cause systemic disease
 
**Bacteria either destroyed by the phagocytic cells or survive and multiply in the cells to cause systemic disease
 
**Intracellular carriage if bacteria no completely removed
 
**Intracellular carriage if bacteria no completely removed
 +
**Invasive potential of certain strains e.e ''Salmonella'' Dublin associated with carriage of a large plasmid, encoding genes to allow intracellular survival in macrophages and also to allow iron acquisition
 +
**''Salmonellae'' are facultative intracellular organisms, allowing them to move from the gut in macrophages and cause a bacteraemia and lesions throughout the body
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**Possession of Pathogenicity islands associated with virulence
    
===Clinical infections===
 
===Clinical infections===
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 +
*Some serotypes are host-specific, some are not
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*''S.'' Tymphimurium infects many species; causes severe diarrhoea; non-invasive; causes of food poisoning in humans, e.g. from infected poultry
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*''S. enteritidis'': non species-specific; losses in young birds; causes food poisoning in humans
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*''S.'' Dublin: invasive serovar; infects cattle
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*''S.'' Cholerae-Suis: primarily infects pigs; also causes severe human disease
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*''S.'' Pullorum: infects poultry; egg-transmitted; causes bacillary white diarrhoea, known as pullorum disease
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*''S.'' Gallinarum: infectes older birds; known as howl typhoid
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*''S.'' Pullorum and ''S.'' Gallinarum now rare in UK due to eradication programs including the Pullorum test (whole blood slide agglutination to detect antibody to both ''S.'' Pullorum and ''S'' Gallinarum
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*''S.'' Abortis-ovis: infects sheep
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*''S.'' Abortus-equi: infects horses outside of the UK
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*''S.'' Typhi, ''S.'' Paratyphi: infect humans
     
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