![]() Such a relationship has definitively been established in the case of I. Itch was reported at the site of tick bite, and the frequency of itch increases as the number of reported tick bites increase, which strongly suggests that tick-associated itch is associated with an acquired cutaneous hypersensitivity response. These observations suggest that residents of disease-endemic sites who experience persistent tick-associated itch are less likely to develop Lyme disease than are those who do not experience this reaction. Persons who consistently report itching in association with tick bites are less likely to experience an episode of Lyme disease than do those who fail to react against tick bite. Confining the analysis to only those who had Lyme disease illness by omitting participants whose evidence of Lyme disease was by seroconversion alone did not alter the inverse relationship between itch and developing Lyme disease. Consistent with the bivariate analysis, the risk of acquiring Lyme disease was higher for 1 report of itch (OR 2.7, 95% CI 0.4–2.3), and decreased among those who reported itch at >3 study visits (range 3–12, OR 0.18, 95% CI 0.05–0.5) ( Figure 2). We used a multiple logistic regression model to estimate the likelihood of acquiring Lyme disease for participants reporting none to 1, 2, and >3 reports of itch, controlling for number of study visits and reports of tick bite. The probability of itch doubled as the number of reported tick bites increased from 1 to 2 (21% to 46%, respectively) and doubled again from 2 to 4 reported bites (46% to 97%, respectively linear trend p 4 such reports. Among these 610 participants, 52% reported at least 1 tick bite (mean 2.2, 95% CI 2.0–2.4), and 32% reported itch with any tick bite. This analysis was limited to participants whose sera displayed no evidence of tickborne illness before study entry, who had >1 serosurvey visit, and who were >2 years of age. We next determined whether increasing exposure to ticks increases the probability of tick-associated itch. The predicted probability of acquiring Lyme disease was estimated for significant risk factors. The relative contribution of risk factors to the acquisition of Lyme disease was evaluated from multiple logistic regression models to calculate odds ratios with associated confidence limits. Bivariate logistic regression was used to estimate probability of itch for increasing tick bites. The results were analyzed with descriptive statistics (mean, proportion, and confidence intervals with 5% error). To create 10-year individual measures, reports of tick bite and itch were summed across all visits for each participant. To determine yearly Lyme disease incidence, we compared the number of new cases of Lyme disease each year to the total number of study participants who had enrolled in the study up to that time. To estimate the study sample frequency of tick bite and tick-associated itch, we averaged the individual reports of tick bite and tick-associated itch among study participants each year. In particular, we determined whether residents of Block Island, Rhode Island, who experienced itching associated with attached ticks have fewer episodes of Lyme disease than those who report no episodes of itching associated with tick attachment.Īll statistical calculations were performed with JMP 5.1 (SAS Institute, Cary, NC). ![]() Accordingly, we determined whether cutaneous hypersensitivity against tick antigens increases with the frequency of tick exposure and whether such reactivity protects against Lyme disease. ![]() The epidemiologic relevance of host immunity to tick bite for preventing Lyme disease remains unknown.Īcquired immunity to vector ticks may limit the incidence of Lyme disease by protecting persons who have been previously exposed to bites of vector ticks. Additional inflammatory reaction to tick salivary proteins also may help prevent transmission ( 10 – 11). Itching provides an early sign of tick bite and may facilitate removal of the attached tick before the pathogen can be transmitted. Repeated exposure to tick bites has been associated with developing cutaneous hypersensitivity, which results in persistent itch and local swelling at the site of tick attachment ( 12 – 13). Other variables that might restrict Lyme disease incidence include prompt removal of attached ticks before the pathogen is transmitted and acquired immunity to the salivary proteins of these ticks, the spirochetal pathogen, or both ( 7 – 11). This disparity reflects both a relative paucity of spirochetal infection in vector ticks and the limited number of people actually bitten by ticks ( 5 – 6). Although many residents of Lyme disease–endemic regions describe frequent exposure to ticks, relatively few become infected by the causative spirochetal agent, Borrelia burgdorferi ( 1 – 4).
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