FAMILY RICKETTSIACEAE 



1087 



demic (murine) typhus which is trans- 

 mitted to man by the rat flea. 



3. Rickettsia rickettsii (Wolbach) 

 Brumpt. {Dermacentroxcnus rickettsi 

 Wolbach, Jour. Med. Res., U, 1919-20, 

 87; Rickettsia rickettsi Brumpt, Precis 

 de Parasitologie, 3rd ed., 1922, 757; 

 Rickettsia brasiliensis Monteiro, Mem. 

 Inst. Butantan, 6, 1931, 3; * Rickettsia 

 typhi do Amaraland Monteiro, Rev. Sud. 

 Am^r. de M6d. et Chirurg., 4, 1933, 806; 

 Dermacentroxenus rickettsi var. brasili- 

 ensis Pinkerton, Parasitology, 28, 1936, 

 186.) Rickettsia dermacentroxenus, a 

 corruption of Dermacentroxenus rickettsi, 

 though widely used, has no genuine 

 taxonomic standing. Named for Howard 

 Taylor Ricketts, who first transmitted 

 the disease from human cases to monkeys 

 and guinea pigs with the production of 

 characteristic symptoms and lesions and 

 fatal effect. 



Minute paired organisms surrounded 

 by a narrow clear zone or halo and often 

 lanceolate, resembling in appearance a 

 minute pair of pneumococci. Approxi- 

 mately 0.2 to 0.3 micron by 1 micron. 

 Non-motile. 



In smears of mammalian tissues there 

 occur in addition to the lanceolate forms, 

 slender rod-shaped forms stained blue 

 with the Giemsa stain, sometimes ex- 

 hibiting polar granules, stained purplish 

 or reddish. There are also minute pale 

 blue-staining rounded forms. In the 

 tick there are three forms: (1) Pale blue 

 bacillary forms curved and club-shaped, 

 (2) smaller bluish rods with deeply 

 staining chromatoid granules and (3) 

 more deeply staining, purplish, lanceo- 

 late forms. A very minute form may 

 appear in tightly packed masses in the 

 nuclei of the cells. Occurs in the cyto- 

 plasm and nucleus in all types of tissue 

 in the tick and in the vascular endothe- 

 lium, in the serosal cells of the peritoneal 



cavity, in the smooth muscle cells of 

 arteriolar walls and in the macrophages 

 of mammals. 



In yolk sac cultures and in the Mait- 

 land media cultures, bacillary forms often 

 occur in pairs. In single smears from 

 infected yolk sacs, the rickettsiae are 

 rather uniform in size and morphology 

 and are definitely lai'ger than Rickettsia 

 prowazekii and Rickettsia typhi. They 

 also grow more sparsely. Stain blue with 

 the Castaiieda stain and bright red 

 against a blue background of tissue with 

 the Machiavello stain. 



Cultivation : May be cultivated in 

 plasma tissue culture of mammalian 

 cells, in Maitland media with and with- 

 out agar, on the chorio-allantoic mem- 

 brane and in the yolk sac of the chick 

 embryo, and in ticks. 



Optimum temperature 32°C in plasma 

 tissue culture, 35°C in chick embryo 

 cells. 



Immunology : Prolonged immunity in 

 man and animals after recovery from in- 

 fection. Killed vaccines produced from 

 infected ticks and from infected yolk 

 sacs afford considerable protection 

 against the disease. Therapeutic anti- 

 sera have been produced by the injection 

 of rabbits with tick virus and with in- 

 fected yolk sac. No cross immunity 

 between spotted fever in guinea pigs 

 recovered from infections with Rickett- 

 sia rickettsii and typhus in guinea pigs 

 recovered from infections with Rickettsia 

 prowazekii and Rickettsia typhi. Cross 

 immunity between spotted fever in 

 guinea pigs recovered from infections 

 with Rickettsia rickettsii and bouton- 

 neuse fever in guinea pigs recovered from 

 infections with Rickettsia conorii, but 

 spotted fever vaccine does not protect 

 against boutonneuse fever of the Medi- 

 terranean area or against infections with 

 the South African strains of Rickettsia 

 conorii. 



* Erroneously applied by do Amaral and Monteiro to the so-called eastern type 

 of Rocky Mountain spotted fever. — Editors. 



