prowazekii

Rickettsia prowazekii is a Gram-negative, obligate intracellular bacterium of the genus Rickettsia. It is the causative agent of epidemic typhus in humans and is classified within the family Rickettsiaceae, order Rickettsiales, class Alphaproteobacteria. As an obligate intracellular organism, it cannot be grown on standard bacteriologic media and requires living cells or embryonated eggs for culture, under specialized laboratory conditions.

Transmission occurs primarily via the human body louse, Pediculus humanus corporis. Lice become infected by feeding on an infected person, and transmission to a new host occurs mainly when louse feces containing the organism are scratched into skin breaks or mucous membranes. Epidemics are associated with overcrowding and poor hygiene. Humans are the main reservoir; there is no essential animal reservoir for sustained transmission.

Pathogenesis involves invasion of endothelial cells and the induction of widespread vasculitis, leading to fever, malaise, severe headache, myalgia, and a maculopapular rash that typically begins on the trunk and can spread to the limbs. Severe disease can include meningoencephalitis, pneumonia, and hypotension. Without treatment, mortality has been historically high; antibiotic therapy markedly reduces fatality. Latent infection can reactivate years later as Brill-Zinsser disease.

Diagnosis relies on serology, particularly indirect immunofluorescence assays, and molecular methods such as PCR. Culture is hazardous and restricted to specialized laboratories (BSL-3). First-line treatment is doxycycline for adults and children; alternatives include chloramphenicol in certain circumstances, with careful consideration in pregnancy.

Prevention focuses on delousing, improved hygiene, and vector control to reduce transmission. There is no widely used vaccine for epidemic typhus.