DISEASES CAUSED OR CARRIED BY MITES AND TICKS 413 



tion of the cause of the disease and proved transmission of the disease 

 to a guinea pig by Dermacentor andersoni Stiles {occidentalis Stiles, not 

 Marx). This preliminary report by Ricketts was followed by numerous 

 other papers by himself on the subject, until he had definitely proven the 

 relationship of the tick to the disease. The organism causing spotted 

 fever has just been described. Wilson and Chowning described Piroplasma 

 hominis as the causative organism, but their work has not been corrob- 

 orated by others. Very recently Wolbach (1919) has found bodies some- 

 what similar to the Rickettsia bodies found in typhus fever and trench 

 fever. He describes his organism as Dermacentroxenus rickettsi Wol- 

 bach, but is uncertain as to its location in classification. It is intra- 

 cellular in mammal and tick, and intranuclear in ticks. Two multiplica- 

 tive forms and an infective form are found in the tick, and only the latter 

 is regularly found in mammals. Wolbach's volume is the latest and most 

 complete treatise on all phases of the disease and is well illustrated. 



Mayer (1911) conducted transmission experiments and was success- 

 ful in transmitting the disease by Dermacentor margmatus Banks, 

 Amhlyomma americanum (Linnaeus) Koch and Dermacentor variabilis 

 (Say) Banks. 



The role of wild animals in acting as reservoirs for the disease has not 

 been definitely determined although several wild mammals have been shown 

 to be susceptible. It is probable that it is by this means that the disease 

 is perpetuated. The ticks which carry the disease are normally found 

 on wild animals in the immature stages and the adults usually engorge 

 on the larger domestic animals and to some extent on the larger wild 

 mammals. The Rocky Mountain Spotted Fever is transmitted heredi- 

 tarily by the tick. Control of the disease must be effected by destruction 

 of the adult ticks on domestic animals, reduction of the numbers of wild 

 hosts, and prevention of tick attack on man. 



TSUTSUGAMUSHI DISEASE, sometimes called JAI^ANESE 

 RIVER FEVER or KEDANI DISEASE, has been proven to be carried 

 by the mite Leptus akamushi Brumpt (Trombidium) . Kitashima and 

 Miyajima have proven that this disease is not caused by the bite of all 

 mites of this species, but only by certain ones, and consider that the evi- 

 dence is sufficiently strong to assume that the disease is caused by a non- 

 filterable virus. which can be inoculated by the mites only after they have 

 become infected. They conducted a large number of experiments to prove 

 the role of the mite. The field mouse, Microtus montebelli, is susceptible 

 and is believed to be the important natural host of the virus. (It is inter- 

 esting to note that another Japanese disease. Seven Day Fever, caused by 

 Leptospira hebdomadis Ido, Ito and Wani has the same mouse, Microtus 

 montebelli as its reservoir.) 



