key: cord-0314073-vbejnijg authors: Fowler, Peter D.; Nguyentran, S.; Quatroche, L.; Porter, M.L.; Kobbekaduwa, V.; Tippin, S.; Miller, Guy; Dinh, E.; Foster, E.; Tsao, J.I. title: Northward Expansion of Amblyomma americanum (Acari: Ixodidae) into Southern Michigan date: 2022-02-20 journal: bioRxiv DOI: 10.1101/2021.12.31.474651 sha: 7e209424c255ddfb83c89972bead3d3ce943c23f doc_id: 314073 cord_uid: vbejnijg Amblyomma americanum (Linnaeus) (Acari: Ixodidae) (lone star tick) is an aggressive, generalist parasite that vectors numerous important human and animal pathogens. In recent decades its geographic range has expanded northwards from endemic regions in the southeastern and southcentral US. In 2019 five questing A. americanum comprising two life stages were detected at one site in Berrien County, in southwestern Michigan, satisfying one CDC criterium for an established population for the first time in the state. To better characterize the northern extent of emerging A. americanum, we conducted active surveillance (i.e., drag sampling) in summer 2020 throughout Michigan’s southern counties and detected one adult A. americanum from each of six widespread sites, including where they had been detected in 2019. A larger established population was identified at another site in Berrien County, which yielded 691 A. americanum comprising three life stages. Questing tick phenologies at this site were similar to that reported for other regions. Statewide surveillance in 2021 revealed no A. americanum outside of Berrien County, but establishment criteria were met again at the two sites where established populations were first detected respectively in 2019 and 2020. These observations may represent the initial successful invasion of A. americanum into Michigan. Data from passive (1999-2020) and active surveillance (2004-2021) efforts, including a domestic animal sentinel program (2015-2018), are reported to provide context for this nascent invasion. Continued active surveillance is needed to help inform the public, medical professionals, and public health officials of the health risks associated with this vector. Passive Surveillance Table 1) . (Say) (7.8%), A. americanum (1.2%), I. dentatus (Marx) (0.01%), and Haemaphysalis leporispalustris (Packard) (0.1%). Of the 55 sites sampled, A. americanum was found at 7 sites in five counties across 206 southern Michigan (from west to east: Berrien, Branch, Cass, Ingham, and Huron). Only one site, 207 located in Berrien County, yielded more than one A. americanum and multiple life stages. An additional 208 25,000 m 2 were sampled from May 11 th to July 30 th in 2020 by the Berrien County Health Department, 209 which revealed a single A. americanum from two sites. In 2021, statewide surveillance by MSU for I. 210 scapularis resumed; 373,378 m 2 were sampled and an additional 38,000 m 2 were sampled by BCHD. Larval I. scapularis were detected throughout the study period, with a first peak in July followed by a 244 second peak in September. 345 The criteria for considering a tick species as being established in a given county is important to consider 346 as we seek to understand their spread. Established tick populations as defined by the CDC involves Amblyomma americanum submitted to the MDHHS for the last decade fulfill CDC criteria for some 356 Michigan counties in some years, but the numbers vary widely from year to year, and no county is 357 consistently represented (Figures 1-2) . Additionally, active surveillance from those same years do not Amblyomma americanum is of special concern in emerging areas as many of its associated diseases may 442 not be familiar to medical professionals in the region. Pathogens of concern for human health that A. r r i e n 1 3 3 2 4 0 9 B r a n c h 1 ---H u r o n 1 ---I n g h a m 1 ---2 0 2 1 B e r r i e n 5 1 4 5 5 0 T o t a l 1 1 8 8 2 4 5 9 Table 1 ). The yellow square Figure 3 for the location of the field site. - 2 0 0 5 A l l e g a n - 1 - - V a n B u r e n - 1 - - 2 0 0 7 B a r r y - - 1 - 2 0 1 7 V a n B u r e n 1 - - - 2 0 1 9 B e r r i e n 1 - 4 - M u s k e g o n - 1 - - 2 0 2 0 B e Black dots mark field sampling sites See Table 1). The yellow square 795 marks the established population of A. americanum at Grand Mere State Park Yellow star marks a site sampled regularly as a reference for I. scapularis in order to ensure they are 797 active regionally when sampling other sites. Only the first three visits for this site (i.e., during the 798 nymphal host-seeking period) were included in the effort calculations for each year so as not to skew 799 overall county effort 480 We thank S. Hamer, G.J. Hickling, and E.D. Walker for their contributions to beginning the long-term 481 surveillance studies of invasive ticks in Michigan from which subsequent efforts have grown. Similarly,