374 DISEASES OF UNCERTAIN ETIOLOGY 



SPOTTED FEVER OF THE ROCKY MOUNTAINS. 

 DEFINITION. 



An acute endemic, non-contagious, febrile disorder, with a petechial 

 or papuric eruption following the bites of infected ticks. It is found 

 in valleys, in siiarply defined areas, and occurs at definite times and 

 seasons. 



DISTRIBUTION. 



The United States only. 



In Montana it is found along the Bitter Root valley, at Rock 

 Creek, and Bridger. 



In Idaho throughout the entire valley of the Snake River and its 

 tributaries. 



In Wyoming at Cody and Meeteeste. 



In Nevada, in the north only, along the valley of the Quinn River. 



In Oregon towards Idaho in the east only. 



The fever occurs in those seasons when the ticks (D. andersoni) 

 are most prevalent. 



The elevation is in all cases between 3,000 and 4,000 feet above 

 sea-level. 



AETIOLOGY. 



The causative parasite is stated to be localized in the endothelial 

 cells and smooth muscle fibres (Wolback). Its exact nature is not 

 known. 



The organism is said to be present in the blood-vessels of man, 

 monkeys, rabbits, guinea-pigs and ticks. 



The virus cannot be separated from the blood cells by washing, 

 neither will it pass through a Berkefeld filter. 



One attack produces immunity. 



The virus can be acquired and transmitted by the larvae, nymph, 

 male and female adults of D. andersoni. 



Other ticks are also suspected. 



Men are more frequently attacked than women, commonly from 

 fifteen to fifty years of age. Hence with out-door work there is greater 

 risk of infection. 



Jack rabbits and deer mice are important hosts of the carrier ticks 

 as well as domestic animals. 



PATHOLOGY. 



Post mortem, rigor mortis is well marked. PetechicC are found on 

 the skin. 



Tick bites may be visible. Liver and spleen are congested, 



