Typhoid fever pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aysha Anwar, M.B.B.S[2]

Pathogenesis

The pathogenesis of typhoid fever consists of following sequence of events.

Innoculation

• Orofecal transmission.
• Infective dose 1000 to 1 million organisms.

Gastrointestinal Infection

Stomach

• Bacterium enters stomach.
• Survives pH as low as 1.5

Small intestine

• Adherence to mucosal cells via special proteins.
• Invade mucosal M cells overlying peyer's patches
• Internalisation in M cells of ileum.
• Translocation to underlying lymphoid tissue and draining lymph nodes.

Systemic spread

• Dissemination of S.typhi to reticuloendothelial system.
• Spreads via lymph and blood
• Replication within reticuloendothelial system such as spleen, liver, bone marrow.
• Evades immune system by hiding intracellularly within macrophages.

Chronic carrier state

• Resides and multiplies in gall bladder
• Excretion in urine and stool infecting other individuals.