TYPHUS FEVER, TRENCH FEVER, ETC. 951 



Epidemiology. The distribution of the disease follows that of 

 the wood tick, Dermacentor venustus. The disease occury in Idaho, 

 Montana, Nevada, Wyoming, California, Colorado and Washington. 

 Wolbach notes that the distribution of cases in various states seems 

 to be restricted to definite localities. In Idaho, he finds that the 

 cases are particularly frequent in the Snake River Valley and in 

 Montana in the Bitter Root Valley where there seem to be infectious 

 foci. Seasonally the disease occurs almost entirely in the spring. 



The wood tick named above was associated with the disease first 

 by Wilson and Chowning 40 in 1902. RickeUs brought proof of this 

 in 1906, 47 showing that the disease could be produced in guinea-pigs 

 by allowing wild ticks of this species to feed upon them. McClintic 48 

 confirmed this and his investigations with those of Ricketts, cen- 

 tralized attention upon this particular species, the Dermacentor 

 venustus. Larvae, fed upon infected ticks, remain infective into 

 the nymph stage and the nymph once infected remains infected into 

 the adult stage. He also showed that eggs from infected females 

 would -produce the disease when injected into guinea-pigs and that 

 both male and female ticks would transmit it. Wolbach 's 49 inves- 

 tigations have confirmed most of these points. 



Guinea-pigs infected by ticks develop a temperature in about 

 three to seven days. Injected with blood from other guinea-pigs, 

 the disease may begin at the end of forty-eight hours. Death, which 

 often follows, occurs on the sixth or seventh day. As the disease 

 progresses there is swelling and reddening of the skin of the scrotum, 

 loss of appetite and general signs of illness. There may be redness 

 and swelling of the eye-lids, ears and paws, and ulcers of the paws 

 may form. On autopsy, there may be edema and hemorrhages of 

 the skin and subcutaneous tissues of the scrotum. Male guinea-pigs 

 show the disease most characteristically because of the scrotal lesions. 

 Rabbits are susceptible, although not regularly so. Foot 50 has 

 studied this under Wolbach 's direction. When it does occur 

 in rabbits, the disease is virtually the same as that occurring in 

 guinea-pigs, except that in addition to the other signs of illness, 



49 Wilson and Chowning, Jour. A. M. A., 39, 1902. 



47 Bicketts, Jour. A. M. A., 46, 1906. 



48 McClintic, U. S. Pub. Health and Marino Hosp. Serv., Weekly Bulletin, 

 . 20, 27, 1912. 



" Wolbach, Jour. Med. Research, 41, 1919-1920, 3. 

 , Jour Med., Res., 39, 1919. 



