394 ANNUAL REPOET SMITHSONIAN INSTITUTION, 193 3 



As is well known, the Rocky Mountain spotted fever tick, or wood 

 tick of the Rocky Mountains {Dermacentor andersoni Stiles), con- 

 veys this disease to man in that region. For many years this disease 

 appeared to be limited to the northern Rocky Mountain States, the 

 intermountain region, and the eastern slope of the Cascades. This 

 distribution of the disease was less extensive than that of the trans- 

 mitting tick. In recent years, however, the disease has been recog- 

 nized in many parts of the country far beyond the limits of distribu- 

 tion of the Rocky Mountain spotted fever tick. Obviously, other 

 transmitting agencies are concerned in the region where DerTnacentor 

 andersoni does not occur. In the east the American dog tick, Derma- 

 centor variabilis Say, carries the disease. This is the common wood 

 tick of that region. The mortalit}^ in cases in Mar5dand, Virginia, 

 and the District of Columbia exceeds 20 percent. 



Dr. M. B, Maver, as early as 1911, showed that the western 

 strain of Rocky Mountain spotted fever could be transmitted from 

 diseased to healthy guinea pigs by ticks other than D. andersoni. 

 Her tests were positive with nymphs of the western rabbit tick, 

 D. panmiapertus niarginatus Banks, the lone star tick, AmhlyoTYima 

 americanum Linn., and the American dog tick, D. vanabilis, and 

 also with the adults of the latter. Dr. R. R. Parker has shown that 

 the disease may be transmitted by the rabbit tick, Eaemaphy satis 

 leporis-paliLstris Pack. Positive transmission tests with species rep- 

 resenting such a wide range in relationships and in habits strongly 

 indicate that many other species may be capable vectors. Even 

 though these are the only carriers, their distinction and host rela- 

 tions provide abundant opportunity for the transfer of the disease 

 in every State in the countr3^ 



While no two of the species are exactly coextensive, there are 

 many overlappings in distribution, and in most areas two or more 

 suitable vectors are to be found. The relatively low percentage of 

 individual ticks which become infective would indicate, however, that 

 in many parts of the United States where ticks occur in relatively 

 small numbers, the disease may not become established, even though 

 introduced. 



The bite of a single tick is sufficient to infect a person with the 

 malady. Fortunately, however, the ticks must feed for some time 

 to produce an infection. This time seems to vary from 2 to 8 hours 

 or even longer as shown by experiments carried out by the United 

 States Public Health Service. 



The principal methods of preventing this disease are to avoid tick 

 bites by wearing clothing calculated to exclude the pests, by fre- 

 quent examination of the body for ticks, and by using prophylactic 



