Typhus pathophysiology

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

Pathophysiology

Transmission

• Rickettsial agents are usually not transmissible directly from person to person except by blood transfusion or organ transplantation, although sexual and placental transmission has been proposed for Coxiella.
• Transmission generally occurs via an infected arthropod vector or through exposure to an infected animal reservoir host.

Type of Infection	Spread
Epidemic typhus	Body louse
Trench fever	Body louse
Murine typhus	Flea infested rats
Cat flea rickettsioses	Flea infested dogs and cats
Scrub typhus	Mites
Tick borne rickettsiosis	Ticks
Rickettsialpox	Mites
Anaplasmosis	Ixodes tick
Ehrlichiosis	Lone star tick
Q fever	Infected veterinary animals
Cat scratch disease	Infected cats
Oroya fever	Sandflies

Dissemination

• Scratching a louse-bite site allows the rickettsia-laden excrement to be inoculated into the bite wound.
• Following transmission, rickettsia are ingested by macrophages and polymorphonuclear cells. On ingestion, they replicate intracellularly inside the lysed cells and disseminate systemically.

Incubation

Incubation period of Typhus fever varies from one to two weeks.

Pathogensis

• The major pathology is caused by a vasculitis and its complications.
• On transmission, Rickettsia is actively phagocytosed by the endothelial cells of the small venous, arterial, and capillary vessels.
• It is followed by systemic hematogenous spread resulting in multiple localizing vasculitis.
• This process may cause result in occlusion of blood vessels and initiates inflammatory response (aggregation of leukocytes, macrophages, and platelets) resulting in small nodules.
• Occlusion of supplying blood vessels may cause gangrene of the distal portions of the extremities, nose, ear lobes, and genitalia.
• This vasculitic process also results in loss of intravascular volume with subsequent hypovolemia and decreased tissue perfusion and, possibly, organ failure.