948 



ORDER I. RICKETTSIALES 



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. 



