The Density of the Lyme Disease Vector Ixodes scapularis (Blacklegged Tick) Differs between the Champlain Valley and Green Mountains, Vermont

Abstract

Lyme disease is an emerging infectious disease of public health concern in the northeastern United States. The disease's vector, Ixodes scapularis (Say) (Blacklegged Tick), has increased its range in the past twenty years. In its newly endemic northern range there have been few studies of the Blacklegged Tick's habitat associations. From 2016-2018, we sampled for nymphal Blacklegged Ticks in the Champlain Valley and Green Mountains of Addison County, Vermont, and tested them for Borrelia burgdorferi, the Lyme disease agent. We found 10 times more ticks in the Champlain Valley than in the Green Mountains. Nymphal infection prevalence was 0.21 and did not vary by year or region. The difference in tick density reported has public health consequences, as Vermont has one of the highest rates of Lyme disease in the United States.

Changes in the geographic distribution of the blacklegged tick, Ixodes scapularis, in the United States

“…All life stages of I. scapularis were collected from the three southernmost sites, while only a single nymph was collected at the next most northern site and no I. scapularis of any life stage were collected from the most northern site. Another recent study conducted from 2016 to 2018 in the Champlain Valley of west-central Vermont documented abundant populations of I. scapularis ( Allen et al, 2019 ). Regular future tick surveys across Vermont are of interest to track the proliferation of I. scapularis in the state.…”

“…In Vermont, the number of Lyme disease cases reported annually increased from 105 in 2005 to 623 in 2012 and more than 1000 cases were reported in 2017 with a strong geographical trend of higher incidence in the southwestern corner of the state to near zero in the northeastern section of the state ( Serra et al, 2013 ; Allen et al, 2019 ), suggesting recent colonization of the tick vector from the south. To track trends in the density of host-seeking I. scapularis in Vermont, drag sampling was conducted biweekly from June to December 2011 and from March to June 2012 at five forested sites along a north-south gradient that followed the Connecticut river, which runs along the eastern border of Vermont ( Serra et al, 2013 ).…”

Tick Densities and Infection Prevalence on Coastal Islands in Massachusetts, USA: Establishing a Baseline

“…The distances over which sampling was performed ranged from 0.40 km to 1.65 km per site (Table 1), depending on the local trail system and generally conforming to CDC recommendations to sample along a distance of at least 750 m for estimating tick densities [50]. Shrub thickets and a dense shrub understory in many wooded habitats precluded the use of replicated sampling within multiple plots, as used in other studies, e.g., [15,51,52]. Sampling along public trails allows our sites to be relocated easily by future investigators, including site managers and citizen scientists.…”

“…Drag sampling was carried out between 3 and 30 June 2020, 1 and 26 June 2021, and 29 May and 27 June 2022, coinciding with the period of peak blacklegged nymphal abundance in coastal Massachusetts [20]. At any given site, the number of questing ticks collected during drag sampling can be highly variable from day to day [52,59]. Several steps were taken to standardize our sampling methods.…”