Rickettsia prowazekii (Epidemic or Louse-Borne Typhus)

Rickettsia prowazekii, a small obligately intracellular gram-negative coccobacillus, is the agent of epidemic louse-borne typhus and flying squirrel-associated typhus. It is transmitted between patients by Pediculus humanus corporis, the human body louse, when rickettsia-laden louse feces are scratched into louse-bitten skin or rubbed into mucous membranes. Epidemics occur when poverty, cold climate, overcrowding, and displacement of populations by war, famine, or natural disaster promote louse infestations through poor hygiene. Recovered patients remain latently infected, are susceptible to reactivation with rickettsemia (Brill-Zinsser disease), and can serve as a source for an epidemic. An extrahuman reservoir of R. prowazekii exists in flying squirrels (Glaucomys volans) in eastern North America. Infections associated with close contact to flying squirrels are likely transmitted by mucous membrane or inhalational exposure to the squirrel's infected flea or louse feces. Symptoms of typhus include fever, headache, chills, myalgia, and rash. Untreated illness may progress to cause pulmonary edema, encephalitis, and death. Louse-borne epidemic typhus is associated with severe manifestations and death, whereas flying squirrel-associated typhus appears milder—likely related to the underlying condition and health of those affected. Brill-Zinsser disease (recrudescent typhus) is usually mild and occurs even decades after the initial infection. The indirect immunofluorescence assay is the mainstay of serologic diagnosis. A fourfold rise in immunoglobulin G (IgG) from acute- and convalescent-phase sera confirms the diagnosis. Doxycycline for 7 days is the treatment of choice. Control of body lice by changing and washing garments in hot water is essential for prevention and outbreak control.