tissue cultures, in modified Maitland media, in the yolk sacs of chick embryos and by injection into meal worms and certain other arthropods. Filterability: The infectious agent of Q fever readily passes through Berkefeld N filters, which are impermeable to ordinary bacteria, and W filters, which are imper- meable to typhus fever and spotted fever rickettsiae. Resistance to chemical and physical agents : Comparatively resistant to heat and to drying and chemical agents. Resists 60° C. for 1 hour. Survives in cell-free media at least 109 days without loss of titer. Resis- tant to 0.5 per cent formalin and 1.0 per cent phenol for 24 hours when tested in fertile eggs. Survives several years in dried tick feces. There is complete cross immunity in guinea pigs between strains causing Q fever in various parts of the world; the guinea pigs remain solidly immune to attempted reinfection. A vaccine has been developed which protects cattle and probably labora- tory personnel from infection. Serology: American and Australian strains are identical by agglutination and agglutinin absorption. Strains from various countries are serologically related as shown by complement fixation. Q fever is dis- tinguishable from other rickettsial diseases by complement-fixation tests. No common antigenic factor with any Proteus strain has been demonstrated. Pathogenic for man, guinea pigs and white mice. The monkey, dog, white rat and rab- bit are mildly susceptible. Certain bush animals in Australia, particularly the bandi- coot, have been found naturally infected. Other rodents and marsupials are mildly susceptible. Natural infections occur among cattle, sheep and goats. A febrile reaction occurs in guinea pigs, but the mortality is low except with heavily infected yolk sac, which causes a high mortality. On subcu- taneous or intradermal inoculation, a marked inflammatory thickening of the skin occurs at the site of inoculation. On au- topsy, the spleen is enlarged from 2 to 12 times by weight and is engorged with blood. Passage in guinea pigs and mice is accom- plished by transfer of infected blood, liver and spleen. A febrile reaction often accom- panied by pneumonitis occurs in man, but mortality is nil in uncomplicated cases. Source: First observed by Burnet and Freeman (Med. Jour. Australia, 2, 1937, 299) in stained smears from mice inoculated intraperitoneally with infectious material from Australian patients. Independently, organisms were also seen in preparations of guinea pigs injected with Dermacentor andersoni ticks from "Nine-Mile" area of Montana (U. S. Pub. Health Rep., 53, 1938, 2270). Habitat: Isolated from at least 17 species of naturally infected ticks in North Amer- ica, Australia, Africa, Europe and Asia Minor. Several other species of ticks have been shown experimentally to transmit the agent of Q fever. Transovarial survival occurs in Dermacentor andersoni and Haema- physalis humerosa. The bandicoot {Isoodon macrourus) is probably the natural animal reservoir of the disease in Australia, and the gerbille has been reported in Africa with natural infection. Cows, sheep and goats have been shown to shed organisms in milk and placentas. The etiological agent of Q (for "query," not Queensland as surmised by some writers) fever in man. TRIBE II. EHRLICHIEAE PHILIP, TrIB. NoV. (Ehrlichieae Philip [nomen nudum), Ann. N. Y. Acad. Sci., 56, 1953, 486; also see Canad. Jour. Microbiol., 2, 1956, 262.) Ehr.li.chi'e.ae. M.L. fem.n. Ehrlichia type genus of the tribe; -eae ending to denote a tribe; M.L. fem.pl.n. Ehrlichieae the Ehrlichia tribe. Minute, rickettsia-like organisms pathogenic for certain vertebrate hosts, not including man. Adapted to existence in invertebrates, chiefly arthropods.
