Page:Bergey's manual of determinative bacteriology.djvu/959



Ri.ckett'si.a. M.L. fem.n. Rickettsia named for H. T. Ricketts.

Organisms intracytoplasmic only; insect vectors, no transovarial transmission; OX19 agglutinins stimulated, but no eschar in human host.

The type species of the subgenus is Rickettsia prowazekii da Rocha-Lima.

1. Rickettsia prowazekii da Rocha- Lima, 1916. (Da Rocha-Lima, Berl. klin. Wochnschr., 53, May 22, 1916, 5G7 ; Rickettsia kairo da Rocha-Lima, in Kolle and Wasser- mann, Handb. d. path. Mikroorg., Fischer, Jena, 8, 1930, 1350; Rickettsia exanthemato- typhi Kodama, Kitasato Arch. Exp. Med., 9, 1932, 360; Rickettsia prowazeki var. pro- wazeki Pinkerton, Parasitology, 28, 1936, 186; Rickettsia prowazeki subspecies pro- wazeki Philip, Amer. Jour. Hyg., 37, 1943, 307.) pro.wa.ze'ki.i. M.L. gen. noun prowazekii of Prowazek; named for S. von Prowazek, who lost his life studying typhus fever. Minute, cocco-bacillary, sometimes el- lipsoidal or long, rod-shaped cells which are occasionally filamentous. Often occur in pairs and occasionally in chains. In infected lice the minute coccoid and paired coccoid forms predominate over the short and long rods and over the filamentous forms, which are up to 40 microns in length. Single ele- ments from yolk sacs under the electron microscope average 0.5 by 1.1 microns with maxima of 0.3 to 0.7 by 0.5 to 2.0 microns. In resistant hosts, clumps resembling morulae have been reported in infected cells resembling those seen in some of the other genera. Within the same smear of infected mammalian cells, the organisms are quite uniform in size and morphology. Occur intracytoplasmically in vascular endothelial cells and in serosal cells. Non-motile. Char- acteristically colored purplish with Giemsa stain; the two individuals of a pair are con- nected by a zone of faintly blue-stained material. Colored blue with Castaneda stain and bright red against a blue background with Macchiavello stain. Gram-negative. Cultivation: Growth occurs in plasma tissue cultures of mammalian cells, in the louse intestine, in modified Maitland media with and without agar and in chorio-allan- toic membrane and yolk sac of chick em- bryo, the latter being currently the medium of choice. Mouse and rat lungs have yielded rich harvests following intranasal inocula- tion. Optimum temperature, 32° C. in plasma tissue culture and 35° C. in chick embryo cells. Resistance to chemical and physical agents: Readily inactivated by heat and chemical agents. Death occurs at 50° C. in 15 to 30 minutes; 0.5 per cent phenol and 0.1 per cent formalin also kill the organism. Immunology: Immunity prolonged but may not be permanent in man. Indistin- guishable from endemic (murine) typhus in cross-immunity tests in guinea pigs, but distinguishable from Rocky Mountain spotted fever and other rickettsial diseases in such tests though there is variable reciprocal or partial cross-immunity. Neu- tralizing antibodies are found in the serum of recovered guinea pigs and convalescent persons two to three weeks after deferves- cence. Recrudescence of infection ("Brill's disease") many years after an initial typhus episode without intervention of lice has recently been confirmed. Killed vaccines produced from infected lice, rat lungs and yolk sacs afford a high degree of protection against the disease. Hyperimmune antisera for therapeutic use have been produced in rabbits by injection with infected yolk-sac suspensions and in horses and donkeys with infected mouse- lung suspensions. Atten- uated living strains have also been used successfully in human vaccination.