TEMPORAL CORRELATIONS BETWEEN TICK ABUNDANCE AND PREVALENCE OF TICKS INFECTED WITH BORRELIA-BURGDORFERI AND INCREASING INCIDENCE OF LYME-DISEASE

The abundance of host-seeking Ixodes scapularis nymphs, the principal vector for the Lyme disease agent, Borrelia burgdorferi, in Old Lyme, Lyme, and East Haddam, Connecticut, was compared with the incidence of reported human Lyme disease in the 12-town area around the Connecticu t River and the State of Connecticut for the period 1989 to 1996. Tick s were sampled from lawns and woodlands by dragging flannel over the v egetation and examined for the presence of B. burgdorferi by indirect fluorescent antibody staining. The infection rate of the nymphal ticks by B. burgdorferi during the 9-year period was 14.3% (of 3,866), rang ing from 8.6% (1993) to 24.4% (1996). The incidence of Lyme disease wa s positively correlated with tick abundance in the 12 town area (r = 0 .828) and the State of Connecticut (r = 0.741). An entomological risk index based upon the number of I. scapularis ticks infected by B. burg dorferi was highest in 1992, 1994, and 1996 and was highly correlated with the incidence of Lyme disease in Connecticut (r = 0.944). The num ber of Lyme disease cases has been influenced, in part, by annual chan ges in population densities of I. scapularis and, presumably, a corres ponding change in the risk of contact with infected ticks. Based upon tick activity and spirochetal infection rates, epidemiologically based Lyme disease case reports on a regional scale appear to reflect real trends in disease.