ROCKY MOUNTAIN SPOTTED FEVER 



189 



Spotted Fever Group 



In the Rocky Mountain districts of northwestern United States 

 there exists a disease commonly known as Rocky Mountain 

 spotted fever. In certain parts of Japan and in some of the 

 East Indian Islands and Malay States there occurs a very similar 

 disease known as kedani or flood fever, in Sumatra called pseudo- 

 typhus. These diseases, widely separated as they are, have a 

 remarkable number of points in common. Both are caused by 

 parasites, presumably protozoans, which have not yet been dis- 

 covered; both are transmitted by members of the order Acarina, 

 spotted fever by ticks and 

 kedani by mites, though it is 

 believed that the Sumatra type 

 of kedani may be transmitted 

 by ticks also. Both diseases 

 have a short incubation period, 

 and both follow a very similar 

 course — a skin eruption, con- 

 tinued high fever, and fre- 

 quently high fatality. It is 

 quite probable that these two 

 diseases will be found to be 

 caused by closely related para- 

 sites. Their occurrence in such 

 widely separated localities as 

 northwestern United States 

 and eastern Asia is an inter- 

 esting fact. 



Rocky Mountain Spotted Fever. — For many years certain 

 limited districts in the Rocky Mountain region of northwestern 

 United States (Fig. 58), particularly Idaho and Montana, have 

 been known to be affected by this very serious disease. Its 

 yearly occurrence in well-defined areas has given rise to panic 

 and hysterical fear of entering the " haunted " places. Houses 

 were deserted, land depreciated in value, and some of the richest 

 valleys in the Northwest left unpopulated. In 1906 it was 

 shown by Ricketts that the disease was invariably preceded by 

 the bite of a common local wood-tick, Dermacentor venustus (see 

 p. 361, and Fig. 156), which was experimentally shown to be 

 the intermediate host of the parasite. 



Fig. 58. Map showing distribution of 

 Rocky Mountain spotted fever. Com- 

 piled from U. S. Public Health Reports. 



