FAMILY RICKETTSIACEAE 



1091 



microns. Non-motile. Colored purplish 

 with the Giemsa stain, and red against 

 a blue background with the Machiavello 

 stain. Stains well with azur III and 

 methylene blue. Gram-negative. 



Cultivation : In plasma tissue culture 

 of mammalian cells; on the chorio-allan- 

 toic membrane and in the yolk sac of the 

 chick embryo; in rabbit testes and in the 

 endothelial cells overlying Descemet's 

 membrane of the rabbit eye. 



Immunology : Immunity conferred b}' 

 infection appears less complete than in 

 typhus and Rocky IMountain spotted 

 fever. Strains from several different 

 areas have been found to cross immunize 

 in guinea pigs, but the true relationship 

 of the disease occurring in different 

 localities remains to be determined. 

 Reciprocal cross-immunity between mite 

 strains and human strains has been 

 demonstrated in rabbits, hamsters and 

 mice. 



Serology : Antigens from different 

 strains vary in sensitivity when tested 

 bv complement fixation with immune 

 .ciera. There are probably a number of 

 different types on the basis of comple- 

 ment fixation with immune sera. Has a 

 pr^mmon antigenic factor with Proteus 

 OY-K. 



Re.sistance to chemical and physical 

 aeents : Readily inactivated by heat and 

 chemical agents. Destroyed by a tem- 

 perature of 50°C for 10 minutes, and by 

 0.1 per cent formalin and 0.5 per cent 

 phenol. 



Pathogenicity : Pathogenic for man, 

 monkeys, gibbons, guinea pigs, hamsters, 

 rats, voles, mice, gerbilles, rabbits (by 

 intraocular injection) and chick embryo. 

 There is wide variation in the virulence 

 of different strains for laboratory ani- 

 mals, infection being established with 

 great difficulty with some, while others 

 may cause a high mortality. 



A febrile reaction occurs in guinea pigs. 

 Passage in guinea pigs and mice is ac- 

 complished by inoculation of infected 

 spleen or blood from an infected animal. 



passage in rabbits by intraocular inocu- 

 lation of blood, lymph node or organ 

 emulsions of infected animals. Ascites, 

 enlarged spleen often with a fibrinous 

 deposit are characteristic. 



In man an eschar wifh adenopathy de- 

 velops at the site of the mite bite. In 

 scrub typhus the eschar is not present. 

 A febrile reaction with exanthema occurs 

 and mortality is variable. 



In rabbits infection of Descemet's 

 membrane follows intraocular injection 

 of infected material. 



Source : Seen by Hayashi in smears 

 and sections of the lesion (eschar) at the 

 site of the mite bite and in smears and 

 sections of the adjacent lymph nodes 

 from cases of the disease; also seen by 

 Nagaj^o et al. (loc. cit.) in the endothelial 

 cells overlying Descemet's membrane in 

 rabbits inoculated intraocularly with in- 

 fectious material. 



Habitat: The mites {Trombicula aka- 

 mushi, Tromhicula deliensis syn. T. 

 walchi, Tromhicula fletcheri Sund probably 

 several others). Infective through the 

 ova of the adult female. Only the larvae 

 feed on rodents or man. Reservoir hosts 

 are probablj^ certain wild rodents, in- 

 cluding house and field rats, mice and 

 voles and probably some birds. The 

 etiological agent of tsutsugamushi disease 

 and scrub typhus (for numerous other 

 designations of the disease see Farner 

 and Katsampes, U. S. Naval Med. Bull., 

 43, 1944, 800). 



Note : Rickettsia nipponica Sellards. 

 (Sellards, Amer. Jour. Trop. Med., 3, 

 1923, 545; Rickettsoides nipponica da 

 Rocha-Lima, in Kolle and Wasserman, 

 Handb. d. path. Mikroorganismen, 3 

 Aufl., 8, 1930, 1350.) This problemati- 

 cal organism was thought by its author 

 to be the cause of tsutsugamushi disease. 

 Because it was cultivatible by the meth- 

 ods used by Sellards, it is not now re- 

 garded as identical with Rickettsia tsutsu- 

 gajnushi Ogata. Rickettsoides nipponica 

 is the type species (monotypy) of the 



