Abundance and Borrelia burgdorferi-infection Prevalence of Nymphal Ixodes scapularis Ticks along Forest–Field Edges

Abstract

More than 19,000 human cases of Lyme disease (LD) are reported each year in the United States.Lyme disease cases occur when humans are exposed to the bacterium Borrelia burgdorferi through the bite of an infected ixodid tick. The probability of human exposure to infected ticks results from a combination of human behaviors and entomological risk. Human behaviors include use of tick habitats, use of protective clothing, and grooming for tick removal. Entomological risks include the density of ticks in a habitat and the proportion of these that are infected with B. burgdorferi. Recent studies have suggested that humans are at higher risk of exposure to B. burgdorferi near edges between forests and herbaceous communities, including lawns and old fields, but whether this increased risk is a function of human behaviors, entomological risk, or both, is unknown. We assessed entomological risk across forest-old field edges in Dutchess County, NY. Densities of ticks and of infected ticks were considerably higher within forests than at forest-field edges, and were lowest within fields. Thus, edges between forests and fields do not pose a higher entomological risk than do the forests themselves, although risk at the edge is higher than in herbaceous habitat. Landscapes with abundant edges between forested and herbaceous habitat, and roughly even proportions of both, might attract both heavy human use and pose moderately high entomological risk, and thus could be targeted for mitigation. We suggest that determining appropriate methods for reducing human exposure to LD requires differentiating entomological risk from human behaviors.

Spatial Dynamics of Lyme Disease: A Review

“…Other host species may also be important, especially in influencing abundance of nymphal ticks, which transmit most B. burgdorferi infections to people. An analysis of six forest plots in southeastern New York State over 12 years supported positive correlations between plot-specific densities of nymphal ticks and prior densities of white-footed mice and eastern chipmunks (Ostfeld et al, 2006).…”

“…Densities of adult ticks were positively correlated with those of deer pellet groups, a metric of deer density, at eight sites in southern Maine over 3 years (Rand et al, 2003). In other cases, however, spatial associations between deer and ticks have been weak (Schulze et al, 2001;Jordan and Schulze, 2005), nonexistent (Ostfeld et al, 2006), or even negative (Perkins et al, 2006). Other host species may also be important, especially in influencing abundance of nymphal ticks, which transmit most B. burgdorferi infections to people.…”

“…While edge environments do not have higher entomological risk than adjacent forests (Horobik et al, 2006), it is possible that edges are utilized more frequently or differently by humans, which may result in higher contact rates with infected ticks. Limited research has assessed how human behavior influences LD incidence (e.g., Carroll and Kramer, 2001;Lane et al, 2004) but, to our knowledge, how humans interact with edge habitats has not been tested.…”

Methodological caveats in the environmental modelling and projections of climate niche for ticks, with examples for Ixodes ricinus (Ixodidae)

“…In summary, although climate works at large scales, topography, soil, and vegetation work at finer spatial ones (Thuiller et al, 2004a;Austin and Van Niel, 2011;Triviño et al, 2011;Barbet-Massin et al, 2012). A whole literature exists covering the role of landscape and land use in the performance of health-threatening arthropod vectors (i.e., Estrada-Peña, 2003;Diuk-Wasser et al, 2006;Horobik et al, 2006;Reiter and LaPointe, 2007;Vanwambeke et al, 2007Vanwambeke et al, , 2010, although they may have not reached the popularity or availability of bioclimatic covariates.…”

An Examination of the Demographic and Environmental Variables Correlated with Lyme Disease Emergence in Virginia

“…Therefore, the ecotone between forested and open, vegetated areas supports populations of both white-tailed deer and white-footed mice (Despommier et al 2007). Horobik et al (2007) specifically examined disease transmission risk at the herbaceous-forest ecotone and concluded that, while the proportion of infected ticks and therefore entomological risk was higher in the forest interior, human activity at edges appears to be the driving factor that leads to increased incidence rates in areas with greater levels of herbaceous-forest edges.…”