INCREASING DENSITY AND BORRELIA-BURGDORFERI INFECTION OF DEER-INFESTING IXODES-DAMMINI (ACARI, IXODIDAE) IN MARYLAND

A statewide survey of Ixodes dammini Spielman was done in November 199 1 as a follow-up to a study in 1989. In total, 3,434 adult ticks were collected from 922 hunter-killed white-tailed deer processed at 22 che ck stations (1 per county in 22 of 23 counties in the state). Signific antly more male than female ticks were collected. Tick infestation was significantly heavier on male than female deer. The pattern of tick d istribution was similar to that in 1989, with low prevalence (percenta ge tick-infested deer) and abundance (mean ticks per deer) in the Appa lachian region, moderate values in the Piedmont, and high values in th e western and eastern Coastal Plains regions. The pattern of tick infe ction with Borrelia burgdorferi spirochetes (determined by polyclonal immunofluorescence assay) was similar to the tick distributional patte rn. Overall, tick prevalence and abundance were higher in 1991 than in 1989, as was the spirochete infection rate in ticks. Multiple regress ion analysis of tick prevalence against six selected physical and biot ic parameters (elevation, rainfall, summer and winter temperature, per centage of forest land, deer density) showed a significant relationshi p with rainfall and elevation in 1989 and elevation alone in 1991. A m ore extensive study in Caroline and Dorchester counties in the eastern Coastal Plains region (which showed exceptionally low tick density in dices in a generally tick-abundant region in 1989) demonstrated that I . dammini was well established in Caroline but not in Dorchester Count y.