The objectives of this study were to determine (1) the prevalence of adult ticks of Dermacentor andersoni in national forest recreational sites of Utah, and (2) the incidence of spotted fever rickettsia, Rickettsia rickettsii, in the ticks of these areas. With the use of a white flannel cloth, 358 adult D. andersoni (135 males and 223 females) were collected from 48 recreational sites during the spring and summer of 1964. Ticks from each collection were put in pools, preserved in non-fat skim milk at -30° C, and subsequently tested for the presence of spotted fever rickettsia by guinea pig inoculations. The average collection rate (population density) for all collections was 6.8 per hour, but populations varied between sites. Populations were greater in the middle and southern parts of the state than in the northern. The greatest populations were at elevations between 6,000 and 8,000 feet with the upper limit just under 9,000 feet. The elevational distribution varied with the latitude--greater populations were found at higher elevations in southern than in northern Utah. The season of peak abundance was between the last week of May and the last of June. Populations were greater at lower elevations early in the season and at higher elevations later. Male ticks were more abundant early in the spring whereas females predominated later. The preferred habitat was open, unshaded areas of short, scanty, young grass. Ticks were collected in greater numbers in the afternoon than in the morning. Temperatures between 12° and 38° C apparently had little effect on tick activity. Activity was slightly greater on partly cloudy and cloudy days than on clear days, and increased proportionately relative to an increase in wind velocity. Spotted fever rickettsia were found in 3.6% of the ticks collected. These were from 13 different recreational sites, over half of which are in the northern half of the state near human population centers. Ticks positive for spotted fever were probably infected with avirulent type U or type T strain of R. rickettsii.
College and Department
Plant and Wildlife Sciences
BYU ScholarsArchive Citation
Herrin, C. Selby, "Dermacentor Andersoni and Rocky Mountain spotted fever in national forest recreational sites of Utah" (1966). Theses and Dissertations. 7950.
Rocky Mountain spotted fever; National parks and reserves, Utah