Using geospatial analysis to describe the association between active tick surveillance data and clinical cases of anaplasmosis in Connecticut

Anaplasmosis is a vector-borne disease caused by the bacterium Anaplasma phagocytophilum and is vectored by Ixodes scapularis ticks primarily in the northeastern United States. The Connecticut Department of Public Health designated anaplasmosis a state-wide reportable disease in 2008 and a large increase in cases was witnessed in Connecticut between 2014 and 2019. This study used clinical cases of anaplasmosis reported to the Connecticut Department of Public Health and A. phagocytophilum prevalence data in questing I. scapularis to understand emerging geographic disease hotspots and evaluate potential association between human and I. scapularis infections. Human incidence rates were calculated per 100,000 people by county. I. scapularis infection prevalence was calculated as an acarological risk index using active tick surveillance data from the Connecticut Agricultural Experiment Station. The potential association between incidence rates and acarological risk index was analyzed using Spearman Rank correlation. From 2019 to 2020, 420 human cases of anaplasmosis were reported and 148 A. phagocytophilum-infected I. scapularis were identified in Connecticut and a significant positive correlation was identified between acarological risk index and incidence rates. Active tick surveillance is a helpful tool for identifying geographic areas with increased risk of anaplasmosis and can be useful in guiding public health interventions to prevent cases before they occur while also identifying potential locations where underreporting may occur.