Integrated Assessment of Behavioral and Environmental Risk Factors for Lyme Disease Infection on Block Island, Rhode Island

<div><p>Peridomestic exposure to <i>Borrelia burgdorferi</i>-infected <i>Ixodes scapularis</i> nymphs is considered the dominant means of infection with black-legged tick-borne pathogens in the eastern United States. Population level studies have detected a positive association between the density of infected nymphs and Lyme disease incidence. At a finer spatial scale within endemic communities, studies have focused on individual level risk behaviors, without accounting for differences in peridomestic nymphal density. This study simultaneously assessed the influence of peridomestic tick exposure risk and human behavior risk factors for Lyme disease infection on Block Island, Rhode Island. Tick exposure risk on Block Island properties was estimated using remotely sensed landscape metrics that strongly correlated with tick density at the individual property level. Behavioral risk factors and Lyme disease serology were assessed using a longitudinal serosurvey study. Significant factors associated with Lyme disease positive serology included one or more self-reported previous Lyme disease episodes, wearing protective clothing during outdoor activities, the average number of hours spent daily in tick habitat, the subject’s age and the density of shrub edges on the subject’s property. The best fit multivariate model included previous Lyme diagnoses and age. The strength of this association with previous Lyme disease suggests that the same sector of the population tends to be repeatedly infected. The second best multivariate model included a combination of environmental and behavioral factors, namely hours spent in vegetation, subject’s age, shrub edge density (increase risk) and wearing protective clothing (decrease risk). Our findings highlight the importance of concurrent evaluation of both environmental and behavioral factors to design interventions to reduce the risk of tick-borne infections.</p></div

Land cover classification of Block Island, Rhode Island. Examples of properties with a) low shrub edge density and b) high shrub edge density.

<p>Map shows a Worldview2 image acquired on Sept. 4, 2010 from Digital Globe, Inc.</p

Univariate models.

<p>Univariate logistic regression models of the association between human behaviors and landscape metrics and positive Lyme disease serology. Statistically significant results at p<0.05 are indicated in bold.</p

<i>B</i>. <i>miyamotoi</i> rGlpQ ELISA and Western blot test results among CHR subjects.

<p><i>B</i>. <i>miyamotoi</i> rGlpQ ELISA and Western blot test results among CHR subjects.</p

<i>B</i>. <i>burgdorferi</i> and <i>B</i>. <i>miyamotoi</i> WCL Western blot reactivity in serum samples from New England residents whose sera were reactive against <i>B</i>. <i>burgdorferi</i> and <i>B</i>. <i>miyamotoi</i> antigen.

<p><b>2A.</b><i>B</i>. <i>miyamotoi</i> rGlpQ Western blot results of sera from patients who previously had <i>B</i>. <i>miyamotoi</i> sensu lato infection alone (Bmsl positive control subject, PCR confirmed <i>B</i>. <i>miyamotoi</i> infection) or Lyme disease alone (Bb positive control, erythema migrans rash and <i>B</i>. <i>burgdorferi</i> seropositive using the standard two-step ELISA and Western blot assay). The arrow indicates the rGlpQ specific band. <b>2B.</b> <i>B</i>. <i>miyamotoi</i> and <i>B</i>. <i>burgdorferi</i> WCL Western blot results of sera from the same patients as in Fig 2A.</p