Ticks and Rocky Mountain Spotted Fever of Man 227 



'applied to the arm of a man who had been in the hospital for two 

 months and a half, and had lost both feet from gangrene due to 

 freezing.' On the eighth day the patient became very ill and passed 

 through a mild course of spotted fever, leaving a characteristic 

 eruption. The experiment was repeated by placing the tick on a 

 woman's leg and she likewise was infected with spotted fever." 



The most detailed studies were those of the late Dr. H. T. Ricketts, 

 and it was he who clearly established the tick hypothesis. In the 

 summer of 1906 he found that guinea pigs and monkeys are very 

 susceptible to spotted fever and can readily be infected by inocula- 

 tion of blood from patients suffering from the disease. This opened 

 the way to experimental work on tick transmission. A female tick 

 was fed upon an infected guinea pig for two days, removed and 

 isolated for two days and then placed upon a healthy guinea pig. 

 After an incubation period of three and a half days the experimental 

 animal contracted a well-marked case of the disease. 



A similar result was obtained at the same time by King, and later 

 in the season Ricketts proved that the male tick was also capable 

 of transmitting the disease. He found that there was a very inti- 

 mate relation of the virus to the tick and that the transmission must 

 be regarded as biological throughout. Ticks remained infective as 

 long as they lived and would feed for a period of several months. If 

 they acquired the disease in the larval or nymphal stage they retained 

 it during molting and were infective in the subsequent stages. In a 

 few cases the larvae from an infected female were infective. 



The evidence indicated that the tick suffers from a relatively 

 harmless, generalized infection and the virus proliferates in its 

 body. The disease probably is transferred through the salivary 

 secretion of the tick since inoculation experiments show that the 

 salivary glands of the infected adult contain the virus. 



It is probable that in nature the reservoir of the virus of spotted 

 fever is some one or more of the native small animals. Infected 

 ticks have been found in nature, and as various wild animals are 

 susceptible to the disease, it is obvious that it may exist among them 

 unnoticed. Wilson and Chowning suggested that the ground squir- 

 rel plays the principal role. 



Unfortunately, much confusion exists regarding the correct 

 name of the tick which normally conveys the disease. In the medi- 

 cal literature it is usually referred to as Dermacentor occidentalis , 

 but students of the group now agree that it is specifically distinct. 



