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 squirrel plays the principal rôle.
Unfortunately, much confusion exists regarding the correct name of the tick which normally conveys the disease. In the medical literature it is usually referred to as Dermacentor occidentalis, but students of the group now agree that it is specifically distinct. Banks has designated it as Dermacentor venustus and this name is used in the publications of the Bureau of Entomology. On the other hand, Stiles maintains that the common tick of the Bitter Root Valley, and the form which has been collected by the authors who have worked on Rocky Mountain spotted fever in that region, is separable from D. venustus, and he has described it under the name of Dermacentor andersoni.
Mayer (1911) has shown experimentally that spotted fever may be transmitted by several different species of ticks, notably Dermacentor marginatus, Dermacentor variabilis and Amblyomma americanum. This being the case, the question of the exact systematic status of the species experimented upon in the Bitter Root Valley becomes less important, for since Dermacentor occidentalis, Dermacentor venustus and Dermacentor andersoni all readily attack man, it is probable that either species would readily disseminate the disease if it should spread into their range.
Hunter and Bishop (1911) have emphasized the fact that in the eastern and southern United States there occur several species which attack man, and any one of which might transmit the disease from animal to animal and from animal to man. The following species, they state, would probably be of principal importance in the Southern and Eastern States: the lone star tick (Amblyomma americanum); the American dog tick (Dermacentor variabilis); and the gulf-coast tick (Amblyomma maculatum). In the extreme southern portions of Texas, Amblyomma cajennense, is a common pest of man.
Since the evidence all indicates that Rocky Mountain spotted fever is transmitted solely by the tick, and that some of the wild animals serve as reservoirs of the virus, it is obvious that personal prophylaxis consists in avoiding the ticks as fully as possible, and in quickly removing those which do attack. General measures along the line of tick eradication must be carried out if the disease is to be controlled. That such measures are feasible has been shown by the work which has been done in controlling the tick-borne Texas fever of cattle, and by such work as has already been done against the spotted fever tick, which occurs on both wild and domestic animals. Detailed consideration of these measures is to be found in the publications of the Public Health and Marine Hospital Service, and the Bureau of Entomology. Hunter and Bishopp give the following summarized recommendations for control or eradication measures in the Bitter Root Valley.
(1) A campaign of education, whereby all the residents of the valley will be made thoroughly familiar with the feasibility of the plan of eradication, and with what it will mean in the development of the valley.
(2) The obtaining of legislation to make it possible to dip or oil all live stock in the Bitter Root Valley.
(3) The obtaining of an accurate census of the horses, cattle, sheep, mules, and dogs in the valley.
(4) The construction of ten or more dipping vats.
(5) The providing of materials to be used in the dipping mixture.