... Understanding Pennsylvania Tick Population and Tick-borne Disease Dynamics: A Retrospective Analysis of Archived Databases from 2008-2020 Nishi Natalia, Julia Sendatch, Heidi St. John, Richard Stewart, Marcie L. Lehman, Christina Farris, and Alison Luce-Fedrow Biology Department of Shippensburg University United States Naval Medical Research Center Introduction Ticks have been widely studied for their importance in disease transmission. In Pennsylvania, four different ticks (associated with human diseases) are commonly encountered: (1) Dermacentor variabilis (Rocky Mountain Spotted Fever); (2) Ixodes scapularis (Lyme disease); (3) Amblyomma americanum (Ehrlichiosis); and (4) I. cookei (possible Powassan). In addition to the commonly occurring tick species, approximately 25 species have been identified in the state. I. scapularis, which was once primarily found in Central and Eastern PA, can now be found in all counties in PA. In recent years, PA has had the highest confirmed numbers of Lyme disease cases in the United States. The increasing abundance and prevalence of ticks known to vector human pathogens has prompted public health concerns and further research. Despite the devastating consequences, and potentially fatal outcomes of tick-borne diseases, the local/regional distribution of ticks in Pennsylvania is under-investigated with regards to changes in tick populations and tick-borne disease dynamics. Methods Compiled individual databases from 2008-2020 into one master database Date of collection, location, method of collection, species, sex, life stage, engorgement status, and molecular status Quantitative analysis and mapping (ArcGIS Pro version 2.7.3 (Esri, Redlands, CA)) used to conduct comparative analysis of changing geographical distributions, seasonal distribution, and tick life stage Tick-borne microbes (Rickettsia, Ehrlichia, Anaplasma, and Borrelia) were compared for ticks collected from 2008-2016. Sample Site Density Conclusions Results Total Ticks Collected by Year Tick Species Percentage of Total Ticks Collected 2008 2013 2017 131 ticks 72 ticks 875 ticks I. scapularis 6884/17,507 (39.32%) 2010 2014 2018 D. variabilis 2119/17,507 (12.10%) 2 ticks 138 ticks 521 ticks A. americanum 6868/17,507 (39.23%) 2011 2015 2019 Haemaphysalis spp. 112/17,507 (0.64%) 188 ticks 633 ticks 6512 ticks 2012 2016 2020 1442 ticks 93 ticks 6855 ticks Total Table 2. Major species collected included Ixodes scapularis (39.32%), Amblyomma americanum (39.23%), and Dermacentor variabilis (12.10%). Emergence of two previously rare/unknown ticks in Pennsylvania, A. americanum (2017) and Haemaphysalis (2015), with significant prevalence from 2018-2020. 17,507 ticks Table 1 and Figure 1. A total of 17,507 ticks were collected. Major collecting years included 2012 (n = 1,442), 2019 (n = 6,512), and 2020 (n = 6,855), with concentrations centered around western and central Pennsylvania, but a presence in statewide geographical distribution Pennsylvania 2008-2020 Pathogen qPCR positive ticks Rickettsia 169/793 (21.31%) B. burgdorferi 108/852 (12.68%) E. chaffeensis 59/802 (7.36%) A. phagocyptophilum 15/550 (2.73%) Borrelia spp. 143/377 (37.93%) Table 3. Molecular testing (qPCR) of ticks from 2008-2016 demonstrated Rickettsia (21.31%) and Borrelia burgdorgeri (12.68%) as the most commonly detected tick-borne microbes. The views expressed in this article are those of the author and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, the U.S. Government, nor the Henry M. Jackson Foundation for the Advancement of Medicine, Inc. (HJF). Authors, as employees of the U.S. Government (CMF), conducted the work as part of their official duties. Title 17 U.S.C. 105 provides that 'Copyright protection under this title is not available for any work of the United States Government.' Title 17 U.S.C. 101 defines a U.S. Government work is a work prepared by an employee of the U.S. Government as part of the person's official duties. The study protocol was approved by the Shippensburg University Institutional Animal Care and Use Committee (Shippensburg University IACUC protocol #R02-03-19) in compliance with all applicable federal regulations governing the protection of animals and research. Esri, HERE, NPS, HERE, Garmin, USGS, EPA, NPS Further investigation will examine host association of tick species and the molecular status of ticks that are positive or negative for these pathogens from 2016-2020 Esri, HERE, Garmin, NGA, USGS, NPS I. scapularis and D. variabilis have been present in PA since 2008. A. americanum and Haemaphysalis species are emerging species in the state. Rickettsia and B. burgdorferi are most prevalent among the species of ticks tested. E. chaffeensis and A. phagocytophilum are hypothesized to increase in prevalence. Implications Application in the medical field: provide insight on tickborne illness prevalence in PA Provide pertinent background information for future researchers and epidemiologists Future Research Molecular testing of ticks from 2016-2020 Further expanded surveying of ticks in Pennsylvania REFERENCES 1.Steere, A.C., J. Coburn, and L. Glickstein, The emergence of Lyme disease. J Clin Invest, 2004. 2.USACHPPM. 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