Hypersensitivity to ticks and Lyme disease risk.

Although residents of Lyme disease–endemic regions describe frequent exposure to ticks, Lyme disease develops in relatively few. To determine whether people who experience cutaneous hypersensitivity against tick bite have fewer episodes of Lyme disease than those who do not, we examined several factors that might restrict the incidence of Lyme disease among residents of Block Island, Rhode Island. Of 1,498 study participants, 27% (95% confidence interval [CI] 23%–31%) reported >1 tick bites, and 17% (95% CI 13%–21%) reported itch associated with tick bite in the previous year. Borrelia burgdorferi infected 23% (95% CI 20%–26%) of 135 nymphal Ixodes scapularis (I. dammini) ticks. The likelihood of Lyme disease infection decreased with >3 reports of tick-associated itch (odds ratio 0.14, 95% CI 0.94–0.03, p = 0.01). Prior exposure to uninfected vector ticks protects residents of disease-endemic sites from Lyme disease.