Serology: Strains from various parts of the world are closely related as determined by complement fixation, are distinguishable from other rickettsiae by agglutination, complement fixation and precipitin tests, have a common antigenic factor (alkali - stable polysaccharide) with Proteus OX19 and have a soluble antigen in yolk culture. Lethal effect: Heavily infected yolk-sac cultures injected intravenously or intra- peritoneally are fatal to white mice in a few hours. The toxin, in neutralization tests, has been shown to be specific and is distin- guishable from murine typhus toxin. Pathogenic for man, apes, monkeys, guinea pigs, cotton rats, gerbilles and the louse {Pediculus humanus). Inapparent infections occur in white mice, white rats and rabbits. A characteristic febrile reac- tion with no mortality and usually without scrotal swelling occurs in the guinea pig. Passage in guinea pigs is accomplished by transfer of blood or brain from infected ani- mals; causes a febrile disease with exan- thema and high mortality in man. Does not persist for extended periods in brains of white rats compared to endemic (murine) typhus. A characteristic skin reaction can be produced in recovered rabbits and man. Source: Observed sparingly in the blood of typhus patients and abundantly in smears of epithelial cells of the intestinal tracts of lice fed on typhus patients. Habitat : Found in the body louse {Pedic- ulus hmnanus var. humanus), head louse (P. humanus var. capitis) and monkey louse {Pedicinus longiceps). The etiological agent of epidemic typhus (European typhus, classical typhus, typhus exanthematicus). Man is the probable animal reservoir. 2. Rickettsia typhi (Wolbach and Todd, 1920) Philip, 1943. {Dermacentroxenus typhi Wolbach and Todd (not Tood), Ann. Inst. Past., 34, 1920, 158; minute intracellular bodies, Mooser, Jour. Inf. Dis., 43, 1928, 261; Rickettsia manchuriae Kodama, Taka- hashi and Kono, Saikingaku-Zasshi (Jap.), No. 426, 427, Aug. and Sept., 1931; see Kodama, Kono and Takahashi bibliog- raphy, Kitasato Arch. Exp. Med., 9, 1932, 95; Rickettsia mooseri Monteiro, Mem. Inst. Butantan, 6, 1931, 97 (pub. July, 1932); see Franco do Amaral and Monteiro, bib- liography, Mem. Inst. Butantan, 7, 1932, 367; Rickettsia exanthematofebri Kodama, Kitasato Arch. Exp. Med., 9, 1932, 360; Rickettsia muricola Monteiro and Fonseca, Brasil Med., 46, 1932, 1022; Rickettsia murina and Rickettsia fletcheri Megaw, Trans. Roy. Soc. Trop. Med. Hyg., 29, 1935, 105; Rickett- sia prowazeki var. mooseri Pinkerton, Para- sitology, 28, 1936, 185; Rickettsia prowazeki subsp. typhi Philip, Amer. Jour. Hyg., 37, 1943, 304; Rickettsia typhi Philip, loc. cit.; not Rickettsia typhi Franco do Amaral and Monteiro, Rev. Sud. Amer. de Med. et Chirug., 4, 1933, 806; Rickettsia murina mooseri Veintemillas, Tratado sobre rickett- siasis, etc., Bolivia, 1944, 100.) ty'phi. Gr. noun typhus cloud, hence stupor arising from fever; M.L. noun typhus fever, typhus; M.L. gen. noun typhi of typhus. Resembles Rickettsia prowazekii morpho- logically and in staining properties but averages slightly smaller, 0.45 by 1.0 micron with individual variation of 0.35 to 0.6 by 0.7 to 1.3 microns, under the electron microscope. Non-motile. Gram-negative. Giroud (1952) proposed the term "typhus murin tropical" for a virulent form in Equa- torial Africa. Cultivation : May be cultivated in plasma tissue culture of mammalian cells, in modi- fied Maitland media with and without agar, in fleas and lice, in the peritoneal cavities of X-rayed rats, in the lungs of white mice and of white rats following intranasal inoculation, in the lungs of rabbits follow- ing intratracheal inoculation and in the chorio-allantoic membrane and the j'olk sac of the chick embryo. Optimum temperature, 35° C. in chick- embryo cells. Immunology: Prolonged immunity in man and animals following infection. Com- plete cross immunity between epidemic and endemic typhus in guinea pigs recovered from infections with Rickettsia prowazekii and R. typhi. No cross immunity between endemic typhus and Rocky Mountain spotted fever, Q fever or tsutsugamushi disease in guinea pigs. Serology: Distinguishable from the rickettsiae of spotted fever, Q fever and
