Sandbox:Aditya

Typhus fever

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

Pathophysiology

Typhus fever is a zoonotic disease, Humans could be infected by bites from ticks, lice, inhalation of the bacteria, and direct contact of bacteria with skin wounds or mucous membranes. Following transmission, white blood cells phagocyte the pathogen and transports it via hematologic or lymphatic route to different organs, specially to those of the reticuloendothelial system. The pathophysiology of typhus fever can be described in the following steps.

Transmission

• Rickettsial pathogens are harboured by parasites such as fleas, lice, mites, and ticks.
• Organisms are transmitted by the bites from these parasites or by the inoculation of infectious fluids or feces from the parasites into the skin.

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Disease	Etiological agent	Vector
Epidemic typhus	Rickettsia prowazekii	Human body louse
Murine typhus	Rickettsia typhi	Infected fleas
Scrub typhus	Orientia tsutsugamushi	Larval mites

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

• 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. The major pathology is caused by vasculitis and its complications.
• This process of inflammatory response (aggregation of leukocytes, macrophages, and platelets) along with occlusion of small blood vessels results in formation of nodules.
• Occlusion of supplying blood vessels also causes gangrene of the distal portions of the extremities, nose, ear lobes, and genitalia.
• This vasculitic process also results destruction of the endothelial cells and leakage of the blood leading to volume depletion and subsequent decreased tissue perfusion and, possibly, organ failure.

Natural history

fatal in 20%–60% of untreated cases

History

• History of travel to endemic areas
• History of tick bite

Symptoms

Most common symptoms

• Fever
• Headache
• Malaise
• Maculopapular, vesicular, or petechial rash
• Eschar
• Nausea and vomiting.

Less common symptoms

• Abdominal pain
• Cough