The Rickettsiae 385 



where it caused a mortality rate as high as 80%. Since these original 

 findings, however, other sections of the United States have reported 

 cases of this disease with mortality rates of only 5%. 



The causative organism is Rickettsia rickettsii transmitted by 

 the bite of infected ticks which may be carried by rodents and 

 other animals in endemic areas. Infected ticks bite these animals 

 and man and thus maintain a reservoir for still other ticks to ac- 

 quire the disease and keep it going. 



One of the diagnostic features of these particular rickettsiae is 

 their predilection for nuclear material in the cells they invade. 

 This intranuclear affinity is in contrast to most other rickettsiae 

 which grow best in the cytoplasm of invaded cells (intracyto- 

 plasmic growth). The reason for these differences of localization 

 within parasitized cells needs further investigation. 



BOUTONNEUSE FEVER 



This disease, caused by Rickettsia conorii, is tick-transmitted 

 and is immunologically related to Rocky Mountain spotted fever. 

 It can be distinguished from this latter disease, however, by cer- 

 tain serological tests. The organism is pathogenic for man and 

 for guinea pigs, and in man it produces localized sores and an in- 

 flammatory reaction in the regional lymph nodes. There is a fever 

 but the mortality rate is low. The disease is also known as Medi- 

 terranean fever and Marseille fever, since it is endemic in this 

 area. 



TYPHUS FEVER 



Typhus fever has played an important role in world history 

 since it flourishes during times of war. The etiological agent was 

 discovered in 1910 by Ricketts. The disease is also commonly re- 

 ferred to as camp fever and jail fever, and it has a death rate vary- 

 ing during epidemics from 5 to 75%. Hans Zinsser, the author of 

 Rats, Lice and History, has presented an excellent review of this 

 and other arthropod-borne diseases. He reported that there is no 

 authenticated evidence of typhus fever before the twelfth century, 

 and that the disease was not epidemic before the sixteenth century. 

 Other historical reviews state that typhus was recognized as long 



