Abstract and Introduction
Abstract
Most tickborne disease studies in the United States are conducted in low-intensity residential development and forested areas, leaving much unknown about urban infection risks. To understand Lyme disease risk in New York, New York, USA, we conducted tick surveys in 24 parks throughout all 5 boroughs and assessed how park connectivity and landscape composition contribute to Ixodes scapularis tick nymphal densities and Borrelia burgdorferi infection. We used circuit theory models to determine how parks differentially maintain landscape connectivity for white-tailed deer, the reproductive host for I. scapularis ticks. We found forested parks with vegetated buffers and increased connectivity had higher nymph densities, and the degree of park connectivity strongly determined B. burgdorferi nymphal infection prevalence. Our study challenges the perspective that tickborne disease risk is restricted to suburban and natural settings and emphasizes the need to understand how green space design affects vector and host communities in areas of emerging urban tickborne disease.
Introduction
Lyme disease, or Lyme borreliosis, is the most commonly reported arthropodborne disease in the United States and Europe.[1] In the eastern United States, this disease is caused by Borrelia burgdorferi sensu stricto (hereafter B. burgdorferi), a spirochete transmitted by the blacklegged tick, Ixodes scapularis, and maintained in a horizontal transmission cycle between larval and nymphal I. scapularis ticks and a vertebrate reservoir host community.[2]I. scapularis ticks vector 6 other tickborne pathogens, including Babesia microti (the cause of human babesiosis) and Anaplasma phagocytophilum (the cause of human granulocytic anaplasmosis). The geographic expansion of these pathogens has followed the spread of their shared vector across the northeastern and midwestern United States over the past 50 years.[3] The range expansion of I. scapularis ticks is attributed to reforestation,[4] the increase in deer populations,[4] and climate-facilitated expansion.[5] Although historically associated with the incursion of suburban and exurban development into rural areas,[4] tickborne diseases are an emerging urban threat, indicated by an unprecedented increase in locally acquired cases in New York City (NYC), NY, USA,[6] and B. burgdorferi–infected I. scapularis in Chicago, IL, USA.[7] In contrast with several European studies on urban Lyme borreliosis,[8] the risk for acquiring B. burgdorferi infection in US cities is unknown.
As tickborne diseases spread into urban areas, key issues are what ecologic and sociobehavioral conditions enable establishment of the enzootic cycle and pathogen spillover to humans. Landscape modification, such as forest fragmentation (breaking up of large continuous forests into smaller patches), has been linked to increased transmission risk for Lyme disease.[9,10] Forest fragmentation increases edge habitat and might reduce host biodiversity by increasing densities of white-footed mice (Peromyscus leucopus), a major host for immature I. scapularis ticks and B. burgdorferi, relative to less competent hosts. Fragmentation might also favor white-tailed deer (Odocoileus virginianus) (hereafter deer), the reproductive host for adult I. scapularis ticks, through increased forage quality and predator release,[9,10] and might bring humans in closer contact with forests and tick vectors, increasing human–tick contact rates.[10] However, extreme fragmentation of suitable habitat patches within an impermeable urban matrix might decrease disease risk if connectivity is reduced to the point of limiting host and tick movement.[11] This connectivity might be partially restored by establishing green spaces and habitat corridors within cities, which can lead to an introduction of tick populations and pathogens into new areas.[7,12,13]
With high human densities in cities, emerging tickborne infections can cause a major public health burden.[12] Human risk for acquiring Lyme disease is dependent on the density and infection prevalence of nymphal I. scapularis ticks, the hazard, or potential source of harm.[14] Thus, understanding the drivers of vector and pathogen distribution is critical for designing effective intervention strategies. Because of increasing incidence of locally acquired Lyme disease cases on Staten Island,[6] a borough of NYC, and the potential for expansion to other boroughs, we sought to determine the hazard posed by I. scapularis ticks in public parks in NYC, and characterize the effect of landscape composition and connectivity in and around parks on nymphal I. scapularis tick densities and B. burgdorferi infection prevalence.
Emerging Infectious Diseases. 2019;25(6):1136-1143. © 2019 Centers for Disease Control and Prevention (CDC)
