Rickettsia prowazekii
Rickettsia prowazekii is the pathogen of epidemic typhus. Its epidemic potential caused it to be listed as a human threat in the Select Agent Program.
Life cycle
The organism's reservoir is the alimentary tract of lice. When a louse carrying R. prowazekii bites a human to drain blood for its own nutrition, the louse defecates as it eats. Since the bite causes itching, the human victim scratches the site, crushes the louse, and drives the excrement into the skin. There is no direct transmission into human blood by an untouched louse.
If the louse does survive the human encounter, it is still doomed, although it acquired R. prowazekii from its bite. Of the arthropod vectors of the various forms of typhus, the louse is the only one that is doomed by the pathogen. [1] The relationship between the louse and R. prowazekii is, in their small world, rather reminiscent of Greek tragedy; the outcome differing only to the extent by which the louse enjoyed, in its lousy way, its meals.
Laboratory characteristics
Like all Rickettsiae, it is a small pleomorphic organism that can assume various shapes, such as a coccus or bacillus. It is cultured and stained only with difficulty, so the diagnosis is principally clinical, and confirmed by various immunologic mechanisms.
Antibiotic sensitivity
The organism has clasically been sensitive to doxycycline and chloramphenicol