Spatial analysis of the distribution of Ixodes dammini (Acari: Ixodidae) on white-tailed deer in Ogle County, Illinois.

The pattern of infestations of Ixodes dammini on white-tailed deer in Ogle County in Illinois was studied through examinations of hunted deer from 1988 to 1990. The Illinois Geographic Information System mapped the spatial distribution of tick infestations on deer and related it to a known endemic focus for I. dammini and Borrelia burgdorferi (Castle Rock State Park), and to a major waterway (Rock River). Second-order neighborhood analysis was used to analyze the spatial distribution of deer around Castle Rock State Park. More than 25% of deer were infested. All deer were clustered around CRSP, but the clustering resulted mostly from clustering of infested deer around CRSP. CRSP is apparently the only important source of tick infestations in Ogle County. Clustering of infested deer did not change during the 3-yr study period. The dispersion pattern of ticks on deer was aggregated, with twice and three times as many ticks collected from bucks as from does and from fawns, respectively. More male ticks than female ticks were collected from infested deer. Of 59 ticks removed from harvested deer in 1990, 5.1% tested positive for B. burgdorferi.