942 



ORDER I. RICKETTSIALES 



also grow more sparsely. Stain blue with the 

 Castaneda stain and bright red against a 

 blue background of tissue with the Mac- 

 chiavello stain. Gram-negative. 



Cultivation: May be cultivated in plasma 

 tissue culture of mammalian cells, in Mait- 

 land media with and without agar, on the 

 chorio-allantoic membrane, in the yolk sac 

 of the chick embryo and in ticks. Growth 

 and toxin production are enhanced in killed 

 embryo continued in incubation 24 hours. 

 Growth in intrarectally injected human- 

 body lice destroys intestinal epithelium and 

 may destroy these insects (Weyer, Acta 

 Tropica, 11, 1954, 193). 



Optimum temperature, 32° C. in plasma 

 tissue culture and 35° C. in chick embrj'o 

 cells. Killed in 10 minutes at 50° C. 



Resistance to chemical and physical 

 agents: Readily inactivated bj^ heat and 

 chemical agents. Destroyed by 0.5 per cent 

 phenol and 0.1 per cent formalin. Destroyed 

 by ordinary desiccation in about 10 hours. 



Immunology: Prolonged immunity in man 

 and animals after recovery from infection. 

 Killed vaccines produced from infected 

 ticks and from infected yolk sacs afford 

 considerable protection against the disease. 

 Therapeutic antisera have been produced 

 by the injection of rabbits with infected 

 tick and yolk-sac suspensions. No cross im- 

 munity between spotted fever in guinea pigs 

 recovered from infections with Rickettsia 

 rickettsii and typhus in guinea pigs re- 

 covered from infections with R. prowazekii 

 and R. typhi. Cross immunity between 

 spotted fever in guinea pigs recovered from 

 infections with 72. rickettsii and boutonneuse 

 fever in guinea pigs recovered from infec- 

 tions with R. conorii. Spotted-fever vaccine 

 does not experimentally protect against the 

 boutonneuse-fever group of infections in the 

 Mediterranean and other Eastern Hemi- 

 sphere areas. 



Serology : Distinguishable from Rickettsia 

 proivazekii and R. typhi by complement fixa- 

 tion and by agglutination with specific anti- 

 gens. Because of confusing cross fixation, 

 the complement-fixation test is inadequate 

 to distinguish between agents of the sub- 

 genus Dermacentroxenus . 



Pathogenic for man, monkeys and guinea 

 pigs. Rabbits and white rats are moderately 



susceptible. Animals susceptible in varj'ing 

 degrees include species of ground squirrels, 

 tree squirrels, chipmunks, cottontail rab- 

 bits, jack rabbits, snowshoe hares, marmots, 

 sheep, dogs, wood rats, weasels, meadow 

 mice and deer mice. In Brazil, the opossum, 

 rabbit, dog and cavy have been found 

 naturally infected, and the Brazilian plains 

 dog, capybara, coati and certain bats are 

 also susceptible. Does not persist in brains 

 of rats and ground squirrels but has been 

 recovered from node tissues of man conva- 

 lescent one year (Parker et al.. Jour. Im- 

 munol., 73, 1954, 383). 



A febrile reaction occurs in guinea pigs 

 with typical scrotal lesions, involving 

 petechial hemorrhages in the skin, which 

 may become necrotic. Virulent strains kill 

 80 to 90 per cent of the animals, milder 

 strains kill 20 to 25 per cent. Passage in 

 guinea pigs is accomplished by transfer of 

 blood, spleen or tunica from infected ani- 

 mals. A febrile reaction accompanied by 

 exanthema occurs in man. Mortality is 

 consistently high in some localities, low in 

 others. 



Comments: In 1906 Ricketts (Jour. Amer. 

 Med. Assoc, 47, 1906, 33) infected monkeys 

 and guinea pigs with blood from patients 

 suffering from Rocky Mountain spotted 

 fever. Later in the same year it was dem- 

 onstrated independently by Ricketts (ibid., 

 358) and by King (U. S. Public Health Re- 

 ports, 21, 1906, 863) that the wood tick 

 Dermacentor andersoni was the primary vec- 

 tor in the Rocky Mountain area. (See How- 

 ard Taylor Ricketts, 1870-1910, Chicago, 

 Univ. of Chicago Press, 1911, 333.) 



Source: Observed by Ricketts (Jour. 

 Amer. Med. Assoc, 52, 1909, 379) in the 

 blood of guinea pigs and monkeys experi- 

 mentally infected with Rockj^ Mountain 

 spotted fever and in the salivary glands, ali- 

 mentary sacs and ovaries of infected ticks 

 as well as in their ova. 



Habitat: Found in the infected wood tick 

 {Dermacentor andersoni) , the dog ticks (D. 

 variabilis and Rhipicephahis sanguineus) , the 

 rabbit ticks {Haemaphy salts leporis-pahis- 

 tris, D. parumapertus and Otobius lagophilus) 

 and in Amblyomma brasiliense, A. cajen- 

 nense, A. striatum, A. americanum and 

 Ixodes dentatus. A number of ticks belonging 



