Estimating Infected Blacklegged Tick Encounters Among Outdoor Workers in Minnesota.

Abstract

Outdoor workers are at increased risk of tick-borne diseases, yet we poorly understand the interaction between occupational risk factors and worker behavior. This study integrates active tick surveillance with worker-reported survey data to assess how occupational behaviors, demographic characteristics, and tick-prevention knowledge influence exposure to infected ticks. We collected blacklegged ticks (Ixodes scapularis) from three Minnesota counties to determine the infection prevalence and density of infected ticks for Borrelia burgdorferi and Anaplasma phagocytophilum. Molecular surveillance was coupled with outdoor worker surveys that ascertained exposure characteristics to model individual-specific probabilities of encountering infected ticks during their job responsibilities. From May to July 2023-2024, 872 ticks were collected, where 45.6% (n = 398) were infected with B. burgdorferi and 7.2% (n = 78) were infected with A. phagocytophilum. Across both years, maximum infected tick densities peaked in Carlos Avery Wildlife Management Area at 0.80 (0.22 [IQR 0.16, 0.48]) per 100 m², were intermediate in Lake Elmo Park Reserve at 0.35 (0.12 [IQR 0.05, 0.18]) per 100 m², and lowest in Whitewater Wildlife Management Area at 0.25 (0.04 [IQR 0.02, 0.13]) per 100 m². Forty-two survey responses revealed individual probabilities of encountering infected ticks ranged from ~ 5 to 65% for B. burgdorferi and ~ 0-25% for A. phagocytophilum. Our results suggest that outdoor workers have a high probability of encountering infected ticks through occupational exposure, which was marginally associated with demographic factors (e.g., age) and preventive behaviors (e.g., tick checks, repellent use). This study reports elevated B. burgdorferi infection prevalence from adult (62.1%) and nymphal (36.5%) blacklegged ticks within Minnesota.