Pathogenesis

The clinical effects of Salmonella inoculation depends upon the organism's virulence factors and host defence factors.

Host factors:

• very young or very old, other illness, immune suppression, gastric hypochlorhydria - infecting dose must usually be greater than 100,000 organism though in the presence of hypochlorhydria, a lower infective dose may cause illness

Virulence factors:

• S. cholerae suis is prone to cause septicaemia
• S. virchow and S. dublin have increased invasive potential
• S. typhimurium may possess specific plasmids increasing virulence

Once infection is established, diarrhoea occurs due to enterotoxin-induced electrolyte transport defects across the intestinal mucosa of the ileum and due to invasive inflammation of the colon and lower ileum.