Epidemic typhus is the prototypical infection of the typhus group of diseases, and the pathophysiology of this illness is representative of the entire category. The arthropod vector of epidemic typhus is the body louse (Pediculus corporis). This is the only vector of the typhus group in which humans are the usual host. Rickettsia prowazekii, which is the etiologic agent of typhus, lives in the alimentary tract of the louse. 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; when the host scratches the site, the lice are crushed, and the Rickettsia-laden excrement is inoculated into the bite wound. The Rickettsia travel to the bloodstream and rickettsemia develops.
Rickettsia parasitize the endothelial cells of the small venous, arterial, and capillary vessels. The organisms proliferate and cause endothelial cellular enlargement with resultant multiorgan vasculitis. This process may cause thrombosis, and small nodules may develop from the deposition of leukocytes, macrophages, and platelets. Gangrene of the distal portions of the extremities, nose, ear lobes, and genitalia may occur as a result of thrombosis of supplying blood vessels. This vasculitic process may also result in loss of intravascular colloid with subsequent hypovolemia and decreased tissue perfusion and, possibly, organ failure. Loss of electrolytes is common.
Some people may have a recrudescent case typhus (Brill-Zinsser disease). After a patient is treated with antibiotics and the disease has seemingly been cured, Rickettsia may linger in the body tissues. Months, years, or even decades after treatment, organisms may reemerge and cause a recurrence of typhus. How the Rickettsia organisms linger silently in a person and by what mechanism recrudescence is mediated are unknown. The presentation of Brill-Zinsser disease is less severe and mortality is much lower than in epidemic typhus. Risk factors that may predispose a person to recrudescence include improper or incomplete antibiotic therapy and malnutrition.
Murine typhus and scrub typhus share the same pathophysiology as epidemic typhus, although they are somewhat milder. The incubation period is approximately 12 days for the typhus group. Prior infection with Rickettsia typhi provides subsequent and long-lasting immunity to reinfection.
Frequency:
- In the US: Approximately 15 documented sporadic cases of active infection with R prowazekii, the etiologic agent of epidemic typhus, have been reported. These occurred in the central and eastern portions of the United States and have been linked with exposure to flying squirrels (Glaucomys volans). The flying squirrel acts as the host for R prowazekii, and transmission to humans is believed to occur via squirrel fleas or lice. Murine typhus occurs in southern California and southern Texas but is not prevalent. Adults are most commonly affected, but infection may occur in any age group. No indigenous cases of scrub typhus have occurred, although infections have been diagnosed in patients returning from endemic areas.
- Internationally: Epidemic typhus occurs in Central and South America, Africa, northern China, and certain regions of the Himalayas. Outbreaks may occur when conditions arise that favor the pro .....
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