Risk of tick-borne pathogen spillover into urban yards in New York City

Abstract

Background: The incidence of tick-borne disease has increased dramatically in recent decades, with urban areas increasingly recognized as high-risk environments for exposure to infected ticks. Green spaces may play a key role in facilitating the invasion of ticks, hosts and pathogens into residential areas, particularly where they connect residential yards with larger natural areas (e.g. parks). However, the factors mediating tick distribution across heterogeneous urban landscapes remain poorly characterized.

Methods: Using generalized linear models in a multimodel inference framework, we determined the residential yard- and local landscape-level features associated with the presence of three tick species of current and growing public health importance in residential yards across Staten Island, a borough of New York City, in the state of New York, USA.

Results: The amount and configuration of canopy cover immediately surrounding residential yards was found to strongly predict the presence of Ixodes scapularis and Amblyomma americanum, but not that of Haemaphysalis longicornis. Within yards, we found a protective effect of fencing against I. scapularis and A. americanum, but not against H. longicornis. For all species, the presence of log and brush piles strongly increased the odds of finding ticks in yards.

Conclusions: The results highlight a considerable risk of tick exposure in residential yards in Staten Island and identify both yard- and landscape-level features associated with their distribution. In particular, the significance of log and brush piles for all three species supports recommendations for yard management as a means of reducing contact with ticks.

Keywords: Amblyomma; Haemaphysalis; Ixodes; Landscape metrics; Urban tick-borne disease.

Fig. 1

Location of sampling sites in Staten Island, New York City (a) and neighborhood characteristics (b). a Buffers, shown in yellow, denote ecological neighborhoods, defined as areas within 500 m of parks, within which houses were primarily sampled. b Demographic and eco-epidemiological information which highlights the variation in tick-borne disease risk and associated risk factors for tick-borne disease across the study area. Tick density refers to the total number of nymphs per 100 m. Lyme cases are the total number of cases reported from each neighborhood from 2010 to 2016. Average household income is given in USD

Fig. 2

Kernel density estimate heatmaps of yards positive for each tick species across Staten Island over 3 field seasons (May—July)

Fig. 3

Biplot of principal component analysis (PCA) for landscape metrics and land cover in 25-m (a), 50-m (b), 100-m (c) and 200-m (d) buffers around residential yards, and examples of yards with low (e) and high (f) PC1 loadings. Abbreviations for landscape metrics: Cohesion, patch cohesion index; enn_mn, mean of Euclidean nearest neighbor; np, number of patches; clumpy, clumpiness index; nlsi, normalized landscape shape index; ai., aggregation index; iji, interspersion and juxtaposition index; mesh, effective mesh size; te, total edge; ed, edge density; lpi, largest patch index; gyrate_mn, mean radius of gyration; contig_mn, mean of contiguity index; tca, total core area; cpland, core area percentage of landscape; ndca, number of disjunct core areas. Abbreviations for landcover classes: Grass, area of grass; low canopy, area of low canopy; high canopy, area of high canopy; impervious, area of impervious surface