tions in appropriate vertebrate hosts of arthropod vectors; intracytoplasmic, occasionally intranuclear in tissues. Etiological agents of epidemic typhus, murine or endemic typhus, Rocky Mountain spotted fever, tsutsugamushi disease, rickettsialpox and other diseases. Many related organisms, described as symbiotes in arthropods not pathogenic for verte- brates, have been assigned here, but information is much less complete than for the patho- genic forms, and their congeneracy with the type species is uncertain. Phylogenetic rela- tionships remain to be established. (Weyer (Acta Tropica, 11, 1954, 194) has recently used comparative growth in human-body lice and meal-worms as a means of studying the rela- tionships of strains of various rickettsias.) The type species is Rickettsia proivazekii da Rocha-Lima.* Key to the species of genus Rickettsia. I. Grow in embryonated chicken eggs; exhibit intracellular parasitism; Proteus OX agglu- tinins are stimulated in human hosts. A. Intracytoplasmic only; transmitted by insects or trombiculid mites. 1. Transmitted by insect vectors, but there is no transovarial transmission; OX 19 agglutinins but no eschar produced in human hosts (Subgenus A, Rickettsia) . a. Louse-borne; animal reservoir in man. 1. Rickettsia prowazekii. aa. Chiefly flea-borne; animal reservoir in rodents. 2. Rickettsia typhi. 2. Transmitted by trombiculid-mite vectors; transovarial transmission; OXK agglutinins and often eschar and adenitis produced in human hosts (Subgenus B, Zinsser a). 3. Rickettsia tsutsugamushi. B. Intracytoplasmic and intranuclear; transmitted by ticks or small tick-like mites with transovarial transmission; OX19 agglutinins (Subgenus C, Dermacentroxenus) . 1. No eschar or adenitis produced in man; specific vaccine affords protection. 4. Rickettsia rickettsii. 2. Eschar and adenitis present; spotted-fever vaccine does not protect. a. Tick transmission demonstrated or presumed. b. High specific, homologous fixation of complement (So. Europe, Asia and Africa). 5. Rickettsia conorii. bb. Complement fixation differs (Australia). 6. Rickettsia australis. aa. Dermanyssid mite-borne (only in urban areas of Atlantic Coast, U. S. A.).t 7. Rickettsia akari. II. Does not grow in embryonated chicken eggs; e.xtracellular growth in gut of body louse; no Proteus OX agglutinins, eschar or adenitis produced in human hosts (Subgenus D, Rochalimaea) . 8. Rickettsia quintana.
- The editors of the Manual follow Recommendation 27d of the International Bacterio-
logical Code in regard to the endings used for the specific epithets. This calls for the use of the ii ending for epithets taken from the name of a man ending in a consonant (except names ending in er). t 0Xi9 Weil-Felix test only occasionally positive; transovarial passage of agent in mite vector has been demonstrated in experimental vector Bdellonyssus bacoti (Philip and Hughes, Amer. Jour. Trop. Med., £8, 1948, 697) and in natural vector, Allodermanyssus sanguineus (Kiselov and Volchanetskaia, in Pavlovsky et al., Nat. Nidi Hum. Dis. and Regional Epidemiol. (Russian), 1955, 251).
