. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. TRANSMITTERS OF SPOTTED FEVER 363 again attack their rodent hosts. After dropping off these and transforming into adults they no longer pay any attention to the rodents but seek larger animals, especially preferring horses and cattle, though they readily attack other large wild and domestic animals and man. Their original wild hosts were probably the mountain goats, elk and other wild game of the region, but with the supplanting of these by domestic animals the latter have become the main host animals o
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. TRANSMITTERS OF SPOTTED FEVER 363 again attack their rodent hosts. After dropping off these and transforming into adults they no longer pay any attention to the rodents but seek larger animals, especially preferring horses and cattle, though they readily attack other large wild and domestic animals and man. Their original wild hosts were probably the mountain goats, elk and other wild game of the region, but with the supplanting of these by domestic animals the latter have become the main host animals of the ticks. Unlike most ticks, this species may take two or even two and a half years to com- plete its life cycle under unfavor- able conditions. The winter is passed in either the nymphal or adult stages. Dermacentor venustus is found in a limited area in northwestern United States and British Columbia, east to eastern Montana and eastern Wyoming, west to the Cascade Mountains and south into Nevada and Colorado. This distribution somewhat exceeds the present dis- tribution of spotted fever (Fig. 58, p. 191). Several different species of ticks have been found capable of trans- mitting spotted fever from rodent to rodent under experimental conditions. Several species of ticks other than D. venustus are found in the spotted fever districts, but none of these can have any hand in the transmission of the disease to man since they do not attack him. A tick closely related to D. venustus, the Pacific wood tick, D. occidentalis, oc- curs west of the Cascades and Sierras in Oregon and California and frequently attacks man. There is little doubt but that if spotted fever once got a foothold in the territory occupied by this tick, the latter would act as an efficient disseminator. In southern and eastern states other ticks which attack man would probably disseminate the disease were it once introduced. For this reason it is of the utmost importance that the infection should not be carr
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