ENTOMOLOGY

DISEASES CAUSED OR CARRIED BY MITES AND TICKS 413tion of the cause of the disease and proved transmission of the diseaseto a guinea pig by Dermacentor andersoni Stiles (occidentalis Stiles, notMarx). This preliminary report by Ricketts was followed by numerousother papers by himself on the subject, until he had definitely proven therelationship of the tick to the disease. The organism causing spottedfever has just been described. Wilson and Chowning described Piroplasmahominis as the causative organism, but their work has not been corroboratedby others. Very recently Wolbach (1919) has found bodies somewhatsimilar to the Rickettsia bodies found in typhus fever and trenchfever. He describes his organism as Dermacentro:cenus riclcettsi Wolbach,but is uncertain as to its location in classification. It is intracellularin mammal and tick, and intranuclear in ticks. Two multiplicativeforms and an infective form are found in the tick, and only the latteris regularly found in mammals. Wolbach's volume is the latest and mostcomplete treatise on all phases of the disease and is well illustrated.Mayer (1911) conducted transmission experiments and waf,! successfulin transmitting the disease by Dermacentor marginatus Banks,Amblyomma americanum (Linnaeus) Koch and Dermacentor variabilis(Say) Banks.The role of wild animals in acting as reservoirs for the disease has notbeen definitely determined although several wild mammals have been shownto be susceptible. It is probable that it is by this means that the diseaseis perpetuated. The ticks which carry the disease are normally foundon wild animals in the immature stages and the adults usually engorgeon the larger domestic animals and to some extent on the larger wildmammals. The Rocky Mountain Spotted Fever is transmitted hereditarilyby the tick. Control of the disease must be effected by destructionof the adult ticks on domestic animals, reduction of the numbers of wildhosts, and prevention of tick attack on man.TSUTSUGAMUSHI DISEASE, sometimes called JAPANESERIVER FEVER or I{EDANI DISEASE, has been proven to be carriedby the mite Leptus akamushi Brumpt (Trombidium). Kitashima andMiyajima have proven that this disease is not caused by the bite of allmites of this species, but only by certain ones, and consider that the evidenceis sufficiently strong ~o assume that the disease is caused by a nonfilterablevirus which can be inoculated by the mites only after they havebecome infected. They conducted a large number of experiments to provethe role of the mite. The field mouse, Microtus montebelli, is susceptibleand is believed to be the important natural host of the virus. (It is interestingto note that another Japanese disease, Seven Day Fever, caused byLeptospira hebdomadis Ida, Ito and Wani has the same mouse, Microtusmontebelli as its reservoir.)