412 SANITARY ENTOMOLOGY 



an important role in producing FISTULOUS WITHERS. He con- 

 siders Dermacentor albipictus Packard as the worst offender, but also 

 considers D. andersoni Stiles {venustus Banks) as a cause. D. albipictus 

 is commonly called a winter tick and in some regions of British Columbia 

 where poll evil and fistulous withers are common, horses are heavily 

 infested with these ticks. The favorite site of attachment is along the 

 whole length of the mane from the poll to the withers. At the point of 

 attachment there is often a necrotic spot if the tick has been attached for 

 a few days. It is easy to see that these necrotic spots should be a 

 favorite point of entrance for bacteria. 



It is quite probable that most of the cases of abscesses and irritation 

 resulting from tick bites are due to secondary infections by bacteria 

 which may possibly be mechanically introduced by the tick itself. No 

 one has given this question serious attention. 



DISEASES OF UNKNOWN ORIGIN 



There are quite a number of instances of so-called tick fever caused by 

 the bite of ticks, of which the exact cause is unknown. Among these are 

 unnamed TICK FEVERS caused by Ornithodoros savigmji Audouin 

 (Koch) and Hyalomma aegyptium (Linnaeus) Koch. 



HEART WATER, a disease of sheep, caused by a filterable virus, is 

 transmitted by Amhlyomma hebraeum Koch. 



The TICK FEVER OF MIANA is caused by the bite of Argas 

 persicus Oken. 



INTERMITTENT FEVER of Wyoming, which is possibly identical 

 with Rocky Mountain Spotted Fever, is thought by Castellani and Chal- 

 mers to be caused by Dermacentor andersoni Stiles {venustus Banks). 



ROCKY MOUNTAIN SPOTTED FEVER, a disease characteristic 

 of the Rocky Mountains of Montana and Idaho and occasionally other 

 nearby states, was proven by Ricketts to be transmitted by tlie tick 

 Dermacentor andersoni Stiles (venustus Banks), by D. variabilis (Say) 

 Banks and possibly by D. modestus Banks. 



The first scientific article in which the tick is mentioned as a possible 

 carrier of this disease was published by Wilson and Chowning in 1902. 

 They subsequently published the reports of their investigations but they 

 did not prove that the tick was actually the transmitting agent. An- 

 derson (1903) was so convinced that the tick was the cause of the fever 

 that he published an article calling it the SPOTTED FEVER or TICK 

 FEVER of the Rocky Mountains, Stiles in 1905 did not attribute the 

 disease to ticks. Finally Ricketts in 1906 began a thorough investiga- 



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