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Epidemic typhus (also called “camp fever”, “jail fever”, “hospital fever”, “ship fever”, “famine fever”, “putrid fever”, “petechial fever”, “Epidemic louse-borne typhus,” and “louse-borne typhus“) is a form of typhus so named because the disease often causes epidemics following wars and natural disasters.
The causative organism is Rickettsia prowazekii, transmitted by the human body louse (Pediculus humanus humanus). Feeding on a human who carries the bacterium infects the louse. R. prowazekii grows in the louse’s gut and is excreted in its feces. The disease is then transmitted to an uninfected human who scratches the louse bite (which itches) and rubs the feces into the wound.
The incubation period is one to two weeks. R. prowazekii can remain viable and virulent in the dried louse feces for many days. Typhus will eventually kill the louse, though the disease will remain viable for many weeks in the dead louse.
After an incubation period of 7 to 14 days, fever, headache, and prostration suddenly occur. Temperature reaches 40° C in several days and remains high, with slight morning remission, for about 2 wk. Headache is generalized and intense. Small, pink macules, which appear on the 4th to 6th day, rapidly cover the body, usually in the axillae and on the upper trunk and not on the palms, soles, and face. Later, the rash becomes dark and maculopapular. In severe cases, the rash becomes petechial and hemorrhagic.
Splenomegaly sometimes occurs. Hypotension occurs in most seriously ill patients. Vascular collapse, renal insufficiency, encephalitic signs, ecchymosis with gangrene, and pneumonia are poor prognostic signs.
Transmission of Epidemic Typhus
- Rickettsia prowazekii is transmitted from human to human by the body louse Pediculus humanus humanus. The head louse (Pediculus humanus capitis) and crab louse (Phthirus pubis) can transmit R. prowazekii experimentally but known epidemics are linked to the body louse.
- Rickettsiae may remain viable and infectious in the dead louse for weeks and in louse faeces for up to 100 days.
- When feeding on an infected human, the body louse ingests R. prowazekii which multiplies in the epithelial cells of the midgut. When these burst, the pathogens are excreted with the faeces of the body louse. R. prowazekii has an impact on the longevity of the body louse and might kill it.
- On average a mature body louse will live for 20–30 days. Body lice multiply rapidly and their population can increase by 11% per day.
- Overcrowding leads to close personal contact and spread of arthropod vectors (particularly lice) among individuals. Humans become infected by contamination of the bite site with infected faeces or through contamination of the conjunctivae or mucous membranes with lice faeces. Presumed infection through aerosols of faeces-infected dust has been reported.
- Rickettsia prowazekii is considered a bioterrorism agent due to specific biological features (notably with regards to environmental stability and possible aerosol transmission).
- While exposed in refugee camps and other settings characterised by crowding and poor hygiene, humanitarian relief workers and military personnel are potentially at higher risk in disease foci than the general population. In general, the risk for travellers is very low as they are applying measures that reduce exposure to body lice during travel.
Treatment for Epidemic Typhus
The infection is treated with antibiotics. Intravenous fluids and oxygen may be needed to stabilize the patient. The mortality rate is 10% to 60%, but is vastly lower (close to zero) if intracellular antibiotics such as tetracycline are used before 8 days. Chloramphenicol is also used. Infection can also be prevented by vaccination.
Immunization and louse control are highly effective for prevention. However, vaccines are not available in the US. Lice may be eliminated by dusting infested people with malathion or lindane.