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===Pathogenesis===
===Pathogenesis===
*Faemcal-oral transmission
*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:
**Degeneration of microvilli
**Degeneration of microvilli
*Systemic disease:
*Systemic disease:
**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
**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
**Possession of Pathogenicity islands associated with virulence
===Clinical infections===
===Clinical infections===
*Some serotypes are host-specific, some are not
*''S.'' Tymphimurium infects many species; causes severe diarrhoea; non-invasive; causes of food poisoning in humans, e.g. from infected poultry
*''S. enteritidis'': non species-specific; losses in young birds; causes food poisoning in humans
*''S.'' Dublin: invasive serovar; infects cattle
*''S.'' Cholerae-Suis: primarily infects pigs; also causes severe human disease
*''S.'' Pullorum: infects poultry; egg-transmitted; causes bacillary white diarrhoea, known as pullorum disease
*''S.'' Gallinarum: infectes older birds; known as howl typhoid
*''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
*''S.'' Abortis-ovis: infects sheep
*''S.'' Abortus-equi: infects horses outside of the UK
*''S.'' Typhi, ''S.'' Paratyphi: infect humans