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Typhus fever

Typhus is defined as a group of diseases caused by bacteria that are spread to humans by fleas, lice, and chiggers.
Typhus fevers include scrub typhus, murine typhus, and epidemic typhus.
Chiggers spread scrub typhus, fleas spread murine typhus, and body lice spread epidemic typhus.
The most common symptoms are fever, headaches, and sometimes rash.

The arthropod vector of epidemic typhus is the body louse (Pediculus corporis).
This is the only vector of the typhus group.
Rickettsia prowazekii,is the etiologic agent of typhus, lives in the alimentary tract of the louse.
A Rickettsia- harboring louse bites a human to engage in a blood meal and causes a pruritic reaction on the host's skin.
The louse defecates as it eats.
Scratching a louse-bite site allows the rickettsia-laden excrement to be inoculated into the bite wound.
The Rickettsia travel to the bloodstream and rickettsemia develops.
The major pathology is caused by a vasculitis and its complications.

Rickettsia parasitize the endothelial cells of the small venous, arterial, and capillary vessels.
The organisms proliferate and cause endothelial cellular enlargement with resultant multiorgan vasculitis.
This process may cause thrombosis, and the deposition of leukocytes, macrophages, and platelets may result in small nodules.
Thrombosis of supplying blood vessels may cause gangrene of the distal portions of the extremities, nose, ear lobes, and genitalia.
This vasculitic process may also result in loss of intravascular colloid with subsequent hypovolemia and decreased tissue perfusion and, possibly, organ failure.