Ticks were collected during 1977 in communities east of the Connecticut River where there was a high incidence of erythema chronicum migrans and
Lyme arthritis and were compared with collections from a similar area 20 km west of the river where cases of the
disease were rare. Ixodes scapularis was much more abundant on the east side than on the west. Immature I. scapularis were 13 times more abundant on white-footed mice (Peromyscus leucopus), and adult I. scapularis 16 times more abundant on white-tailed deer (Odocoileus virginianus) in the east than in the west communities. In addition, all active stages in the life cycle of this tick–larvae, nymphs, and adults–both males and females, were found on humans (mostly patients) in the east communities. Both nymphs and adults were abundant on dogs and cats in this area. Attempts to recover an etiologic agent from ticks were unsuccessful.