190 OTHER SPOROZOA 



Various supposed parasites have been discovered but the dis- 

 coveries have never been substantiated by subsequent investi- 

 gations, and the disease germ of spotted fever is still unknown 

 unless the recent discovery of certain small bodies of supposed 

 protozoan nature by Dr. Fricks should be proved by future in- 

 vestigation to be the true cause of the disease. 



Spotted fever is transmitted by Dermacentor venustus and 

 possibly by other closely allied species of ticks; experimentally 

 it can be transmitted by other ticks, including species found in 

 eastern United States. . The incubation period in the tick is un- 

 known but it is probably only a few days. In man the incubation 

 period is usually from four to seven days. The disease begins 

 with a general feeling of illness followed by chills and aches. A 

 constant fever gradually increases until the tenth or twelfth day, 

 when death is likely to occur. In mild cases the fever gradually 

 subsides during the five or six days following. Usually on the 

 third day a rose-colored rash breaks out on the head and upper 

 part of the body, followed a day or two later by a characteristic 

 spotting of the arms and legs, and later of much of the body, 

 caused by the bursting of blood capillaries in the skin. The 

 spots often become brownish or grayish in color, giving the spotted 

 appearance from which the disease takes its name. In Montana, 

 especially in the Bitter Root Valley, the disease has a high fa- 

 tality, 75 per cent or more of the cases ending in death. The 

 fatality is also high in the endemic parts of eastern Oregon. 

 In Idaho, on the other hand, there is only a 4 per cent or 5 per 

 cent mortality, and this is approximately the case in the other 

 states in which the disease occurs, namely Utah, Wyoming, 

 Nevada, Colorado, Washington and in Lassen County, Cali- 

 fornia. The disease appears only in spring and early summer 

 when ticks are abundant. So far no specific remedy has been 

 discovered. 



There is evidence that spotted fever may be harbored by 

 some of the wild mammals on which the wood tick normally 

 occurs, but this has not yet been proved. The tick, D. venustus, 

 which has been shown to transmit spotted fever is a species 

 which requires two years to reach maturity. In its immature 

 stages it infests many of the local rodents, nearly all of which are 

 susceptible to the disease, and capable of transmitting it to unin- 

 fected ticks. As adults the ticks live on many of the larger wild 



