Spread of Ixodes scapularis (Acari:Ixodidae) in Indiana: collections of adults in 1991-1994 and description of a Borrelia burgdorferi-infected population.

Collection records for the adult black legged tick, Ixodes scapularis Say, in Indiana for the period 1991-1994 are presented and a new, established population of Borrelia burgdorferi-infected I. scapularis is described. The number of I. scapularis adults collected in Indiana increased progressively from 19 in 1991 to > 200 in 1994, and the number of Indiana counties reporting at least 1 adult increased from 13 to 29. Also, during this period, 4 countries in northwestern Indiana yielded > 10 specimens each, and B. burgdorferi-infected ticks were collected in 2 of these counties. An established population of I. scapularis, as evidenced by the presence of questing larvae, nymphs, and adults, was discovered in Jasper County in 1993. Twelve of 39 adults (31%) and 4 of 44 nymphs (9%) collected with cloth drags were infected with B. burgdorferi. Three of 49 (6%) white-footed mice, Peromyscus leucopus, collected from the site were also infected with B. burgdorferi. We believe that this focus was established at least 8 yr ago, and that a tick originating from this focus was responsible for a case of Lyme disease reported from this county in 1985.