Infectious Disease Online
Pathology of Epidemic Typhus (Louse-Borne Typhus) and Brill-Zinsser Disease
Epidemic typhus (louse-borne typhus) is caused by Rickettsia prowazekii.
The arthropod vector of epidemic typhus is the body louse (Pediculus corporis).
The disease is widely distributed in some regions of Africa, Asia, Europe and the Western Hemisphere.
Its devastating epidemics were associated with cold climates, poor sanitation, and crowding during natural disasters, famine, or war as for instance, the epidemics in Russia and easter Europe during 1918-22.
Epidemic typhus may kill 60% or more of the untreated aged, but kills only about 10% of untreated children.
Rickettsia prowazeki is a small gram-negative bacillus (rickettsia) that has a man-louse-man life cycle.
These rickettsiae infect and multiply in human endothelial cells.
Infected endothelial cells detach and rupture, releasing organisms into the circulation (rickettsemia).
A person is usually infectious for lice only during the febrile stage of the disease.
A louse taking a blood meal becomes infected with rickettsiae, after which the organisms enter the epithelial cells of the midgut, multiply, and rupture the cells within 3 to 5 days.
Large numbers of rickettsiae are released into the lumen of the louse intestine.
The louse deposits its contaminated faeces on the skin or clothing of a second host, where the faeces may remain infectious for more than three months.
A person becomes infected when the contaminated louse faeces penetrate an abrasion or scratch in the skin or when the person inhales airborne rickettsiae from clothing contaminating louse faeces.
After penetrating the skin or nasal mucous membrane, the rickettsiae enter the endothelial cells, multiply, and rupture the cells, thus completing the life cycle.
An incubation period of 10 to 14 days is followed by the sudden onset of severe headaches, generalized aching and high fever, which may continue 10 to 14 days before subsiding.
About 4 to 6 days after the onset of symptoms, the patient develops a maculopapular rash on the back, chest, and abdomen.
The rash is composed of 1mm to 4mm "spots", but in fatal cases commonly becomes confluent and purpuric.
Mild rickettsial pneumonia is followed by a severe superimposed bacterial pneumonia.
Although the brain, heart, and kidneys may be involved during the acute phase, patients who recover have no sequelae.
Dying patients may exhibit encephalitis, myocarditis, interstitial rickettsial pneumonia, interstitial nephritis, and shock.
Although rickettsiae do not produce local lesions on entering the skin or respiratory tract, they do cause a generalized vasculitis of minute blood vessels as they multiply within endothelial cells, and fibrin thrombi often form in capillaries, especially those of the brain, skin, and heart.
Fibrin thrombi also occlude blood vessels, and cutaneous necrosis (gangrene of the skin) develops in a few patients.
At autopsy, there are few gross findings except for splenomegaly and occasional areas of necrosis.
However, histologic sections commonly reveal collections of mononuclear cell in various organs, for example, the skin, brain, and heart.
The mononuclear cell infiltrate includes mast cells, lymphocytes, plasma cells and macrophages and are frequently arranged as "typhus nodules" around arterioles and capillaries.
The Brown-Hopps tissue Gram stain (or the Giemsa stain) demonstrates the rickettsiae within endothelial cells.
The rickettsiae divide by biniary fission.
When there are many rickettsiae in an endothelial cell, they are usually lined up in a "flotilla" pattern several columns wide, parallel to each other and to the longitudinal axis of the endothelial cells.
Brill-Zinsser disease is a recrudescence of a latent infection by R. prowazekii in people who have previously had epidemic typhus.
In the past, the disease primarily affected older immigrants from Eastern Europe, especially those who had a weakened immune system.
Years after the initial infection, sporadic illness reappears, characterized by headache, fever and macular rash.
Histologic features are similar to but milder than those for the initial epidemic typhus.
Lice fed with blood from these patients become infected with R. prowazekii.
Epidemic typhus can be controlled by large-scale delousing of the population by, for example, steam sterilization of clothing or use of insecticides.
Tetracycline antibiotics are the preferred treatment for rickettsial diseases.
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