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.

Historical perspective

In 1083, Typhus was first identified as a disease in Spain.
In 1489, during the Spanish siege of Moorish Granada, the first reliable description of the disease was made.
In 1546, Fracastoro extensively described the disease and distinguished it from plague in his book Contagione.
In 1676, Von Zavorziz wrote a book on typhus called The Infection of Military Camps.
In 1739, Huxham provided a clear cut differentiation between typhus and typhoid, later in the same year Boissier de Sauvages confirmed this and called it exanthematic typhus.
In 1836, Gerhard(United States) clearly distinguished the two diseases from each other based on pathologic findings.
In 1926, Maxcy described the various forms of typhus.
In 1909, Charles Nicolle for the first time described the role of lice in transmission of typhus. In 1928, he was awarded the Nobel Prize for his discovery.

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.

class="wikitable"

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.
Endotheleal damage lead to activation of clotting system

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
Prostration
Confusion
Photophobia