FAMILY I. RICKETTSIACEAE 



941 



tions of the adjacent lymph nodes from 

 cases of the disease ; also observed by Ogata 

 (Zent. f. Bakt., I Abt., Orig., 163, 1955, 150) 

 as early as 1927 in preparations of infected 

 rabbit testicles and by Nagayo et al. (op. 

 cit., 1930) in the endothelial cells overlj-ing 

 Descemet's membrane in rabbits inoculated 

 intraocularly with infectious material. 



Habitat: Found in trombiculid mites 

 (particularly Tromhicula akamushi and T. 

 (or var.?) deliensis). Passes through the 

 mite ova to the next generation. Only the 

 larvae are parasitic on vertebrates. Reser- 



voir animal hosts are probably wild rodents, 

 including house and field rats, mice and 

 voles, and probably some birds in which 

 infection may be persistent. The etiological 

 agent of tsutsugamushi disease and of scrub 

 typhus (for numerous other designations of 

 the disease, see Farner and Katsampes, 

 U. S. Naval Med. Bull., ^S, 1944, 800). Many 

 human cases have recently been discovered 

 well south of the classic foci in Japan, and 

 Sasa (Jap. Jour. Exp. Med., 2^, 1954, 335) 

 discusses four epidemiologically distinct 

 "types." 



Subgenus C. Dermacentroxenus (Wolbach, 1919) Philip, 1943. 



(Wolbach, Jour. Med. Res., 41, 1919-20, 87; subgenus Dermacentroxenus Philip, Amer. Jour. 



Hyg., 37, 1943, 304; Acaroxenus Zhdanov and Korenblit, Jour. Microbiol., Epidemiol. 



and Immunobiol. (Russian), No. 9, 1950, 42; Ixodoxenus Zhdanov, Opredelitel 



Virusov Celovska i Zivotmych, Izd. Akad. Med. Nauk, U.S.S.R., Moskau, 



1953, 51 and 155; Garnasoxenus Zhdanov, ibid., 159; see Philip, Canad. 



Jour. Microbiol., 2, 1956, 264.) 



Der.ma.cen.tro'xe.nus. M.L. noun Dermacentor a genus of ticks; Gr. noun xenus host, 



guest; M.L. mas.n. Dermacentroxenus tick dweller. 



Organisms capable of intranuclear parasitism. Produce a typhus-like disease. Trans- 

 mitted by acarid vectors. 

 The type species of the subgenus is Rickettsia rickettsii (Wolbach) Brumpt. 



4. Rickettsia rickettsii (Wolbach, 1919) 

 Brumpt, 1922. {Dermacentroxenus rickettsi 

 (sic) Wolbach, Jour. Med. Res., 41, 1919-20, 

 87; Rickettsia rickettsi (sic) Brumpt, Precis 

 de Parasitologic, 3rd ed., 1922, 757; Rickett- 

 sia brasiliensis Monteiro, Mem. Inst. 

 Butantan, 6, 1931, 3; Rickettsia typhi Franco 

 do Amaral and Monteiro, Rev. Sud. Amer. 

 de Med. et Chirurg., 4, 1933, 806; Derma- 

 centroxenus rickettsi VEiT. brasiliensis Finker- 

 ton. Parasitology, 28, 1936, 186; Rickettsia 

 {Dermacentroxenus) rickettsi Philip, Amer. 

 Jour. Hyg., 37, 1943, 304; Rickettsia colombi- 

 ensis Veintemillas, Tratado sobre rickett- 

 siasis, etc., Bolivia, 1944, 102; Ixodoxenus 

 rickettsi Zhdanov, Opredelitel Virusov 

 Celovska i Zivotmych, Izd. Akad. Med. 

 Nauk, U.S.S.R., Moskau, 1953, 51 and 155.) 



ri.ckett'si.i. M.L. gen. noun rickettsii of 

 Ricketts; named for Howard Taylor Rick- 

 etts, who first saw and described the organ- 

 isms causing Rockj' Mountain spotted fever. 



Minute, paired organisms surrounded by 

 a narrow clear zone or halo; often lanceo- 

 late, resembling in appearance a minute pair 

 of pneumococci. Average 0.6 by 1.2 microns 



under the electron microscope. Non-motile. 

 In smears of mammalian tissues there occur, 

 in addition to the lanceolate forms, slender 

 rod-shaped forms stained blue with Giemsa 

 stain, sometimes exhibiting 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, lanceolate forms. 

 A very minute form may appear in tightly 

 packed masses in the nuclei of the cells. 

 Occurs in the cytoplasm and nucleus in all 

 types of cells in the tick including sperm 

 cells; also occurs in mammals in the vascular 

 endothelium, in macrophages, in the serosal 

 cells of the peritoneal cavity and in smooth- 

 muscle cells of arteriolar walls. In yolk-sac 

 cultures and in the Maitland media cultures, 

 bacillary forms often occur in pairs. In 

 single smears from infected yolk sacs, the 

 cells are rather uniform in size and mor- 

 phology and are definitely larger than those 

 of Rickettsia prowazekii and R. typhi. They 



