A 4-Yr Survey of the Range of Ticks and Tick-Borne Pathogens in the Lehigh Valley Region of Eastern Pennsylvania

Abstract

Questing ticks were surveyed by dragging in forested habitats within the Lehigh Valley region of eastern Pennsylvania for four consecutive summers (2015-2018). A high level of inter-annual variation was found in the density of blacklegged tick nymphs, Ixodes scapularis Say, with a high density of host-seeking nymphs (DON) in summer 2015 and 2017 and a relatively low DON in summer 2016 and 2018. Very few American dog ticks (Dermacentor variabilis Say) and Ixodes cookei Packard were collected. Lone star ticks (Amblyomma americanum L.) and longhorned ticks (Haemaphysalis longicornis Neumann) were not represented among the 6,398 ticks collected. For tick-borne pathogen surveillance, DNA samples from 1,721 I. scapularis nymphs were prepared from specimens collected in summers 2015-2017 and screened using qPCR, high resolution melting analysis, and DNA sequencing when necessary. The overall 3-yr nymphal infection prevalence of Borrelia burgdorferi was 24.8%, Borrelia miyamotoi was 0.3%, Anaplasma phagocytophilum variant-ha was 0.8%, and Babesia microti was 2.8%. Prevalence of coinfection with B. burgdorferi and B. microti as well as B. burgdorferi and A. phagocytophilum variant-ha were significantly higher than would be expected by independent infection. B. burgdorferi nymphal infection prevalence is similar to what other studies have found in the Hudson Valley region of New York, but levels of B. microti and A. phagocytophilum variant-ha nymphal infection prevalence are relatively lower. This study reinforces the urgent need for continued tick and pathogen surveillance in the Lehigh Valley region.

Keywords: Lyme disease; anaplasmosis; babesiosis; surveillance; tick.

Fig. 1.

Location of study sites. AT: Alburtis Mountain Road Tract (40.506, −75.598); LH: Little Lehigh Headwaters Wildlife Park (40.480, −75.694); BP: B. Leroy and Elizabeth Burkhart Preserve (40.516, −75.487); SP: South Mountain Preserve, Wildlands Conservancy (40.547, −75.476); GA: Graver Arboretum of Muhlenberg College (40.800, −75.359); LM: Lehigh Mountain Park 40.604, −75.423); RM: Riemert Memorial Bird Haven, Wildlands Conservancy (40.502, −75.563); RP: Raker Preserve, Muhlenberg College (40.692, −75.706); SM: South Mountain Park (40.599, −75.371); SW: Scholl Woodlands Preserve (40.564, −75.434); TP: Trexler Preserve (40.658, −75.622). Inset, the three shaded counties of Pennsylvania are from right to left, Berks, Lehigh, and Northampton.

Fig. 2.

DON at individual field sites. DON is estimated as the average number I. scapularis nymphs/100 m² in drags that were performed at each site, each year. Abbreviations and locations of sites are shown in Fig. 1. Error bars are represented as SEM.

Fig. 3.

Negative Binomial Regression model for DON based on year. The response variable is nymphs/100 m2 per day, as estimated from time while moving from individual GPX files using GPXSee version 5.17. Each dot on the graph represents the expected nymphs/100 m2 collected using the negative binomial regression model in a particular year. The lower and upper bounds represent the 95% credible interval.

Fig. 4.

B. burgdorferi nymphal infection prevalence at individual sites. Each dot on the graph represents the expected infection prevalence at each site aggregated across the years 2015–2017. The lower and upper bounds represent the 95CI. Abbreviations and locations of sites are shown in Fig. 1.