Pathogenicity and Clinical manifestation of Salmonella Typhi

Pathogenicity and Clinical manifestation of Salmonella Typhi

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Last Updated on May 14, 2020 by Sagar Aryal

Pathogenesis of Salmonella Typhi (Enteric fever/Typhoid fever)

  • Enteric fever is usually caused by strains of Salmonella Typhi & Paratyphi A, B, and C.
  • Enteric fever is generally characterized by infection of reticuloendothelial system & intestinal lymphoid tissue accompanied by sustained fever & bacteremia.
  • The transmission occurs via oral route usually with contaminated foods & water.
  • Salmonella Typhi has an Acid tolerance response (ATR) gene that protects them from the acidity of the stomach.
  • After escaping from the stomach, S. Typhi passes to ileum & colon.
  • It penetrates through the mucosal barrier and is inserted by M-cells (Micro folds-cells of the intestine) or gut epithelial cells through Bacteria mediated endocytosis(BME).
  • BME is mediated by the TypeIII secretory system (TTSS) encoded on Salmonella pathogenicity Island-1 (SPI-1).
  • The bacilli are resistant to the lysosomal content of M-cells & multiply within them.
  • The bacilli are released into underlying lamina propria & presented to the macrophages.
  • They evade killing within the macrophage which is accounted to many virulence traits possessed by S. Typhi such as:
    • Vi-antigen increases resistance to peroxides of macrophages.
    • PhoP & PhoQ gene products modified bacterial LPS.
    • ATR gene products
    • Spv gene products
  • They are then carried by mesenteric lymph nodes to the bloodstream rather than invading adjacent epithelial cells resulting in primary transient bacteremia.
  • The bacilli are phagocytosed into the blood stream by phagocytic cells.
  • These phagocytic cells carry the bacilli into the liver, spleen & bone marrow and they grow within them.
  • After a rapid multiplication, phagocytic cells undergo apoptosis and the bacilli are released into blood stream initiating continuous secondary bacteremia and septicemia.
  • Thus, bacteremia and septicemia are manifested by a daily high fever which is a characteristic of enteric fever.

Pathogenicity and Clinical manifestation of Salmonella Typhi

Image Source: Dahab Clinic.

Clinical Manifestation of Salmonella Typhi

Stage I (1st week)

  1. The slowly rising temperature at 103-104°F.
  2. Malaise
  3. Headache
  4. Abdominal pain & myalgia
  5. Constipation

End of 1st week

  • Dry cough
  • Diarrhea
  • Rose spots may appear on the upper abdomen and on the back of sparse.
  • Abdominal distension with tenderness
  • Splenomegaly

Stage II (2nd week)

  • Signs & symptoms of Stage I progress

End of 2nd week

  • Delirium,
  • The complication and then coma or death (if untreated).

Stage III (3rd week)

  • Febrile become toxic and anorexic.
  • Weight loss
  • Typhoid state ( Apathy, confusion, and psychosis)
  • High risk (5-10%) of hemorrhage and perforation may cause death.

Stage IV (4th week) (Recovery period)

  • If the individual survives to the 4th week, then the fever, mental state, and abdominal distension slowly improve over a few days.
  • Intestinal and neurologic complications may still occur in surviving untreated individuals.
  • Weight loss and debilitating weakness last months.


  2. Greenwood D, Slack RCB, and Peutherer J (2001). Medical Microbiology ELBS,
  3. Pelczar MJ, Chan ECS, and Krieg NR (1993).Microbiology 5th edition,
  4. Cheesbrough M (2007). Medical Laboratory Manual for Tropical Countries Vol.2 ELBS London.


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