Sandbox:Aditya

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.

Pathophysiology

Transmission

• Rickettsial pathogens are transmitted by parasites such as fleas, lice, mites, and ticks.
• Organisms can be transmitted by bites from these parasites or by the inoculation of infectious fluids or feces from the parasites into the skin.
• Inhaling or inoculating conjunctiva with infectious material may also cause infection for some of these organism
• 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.

Dissemination

• 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.

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.
• On entry into the body, the organisms multiply in the endothelial cells, which 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 may also result in loss of intravascular colloid with subsequent hypovolemia and decreased tissue perfusion and, possibly, organ failure.