Influence of Abiotic and Environmental Factors on the Density and Infection Prevalence ofIxodes pacificus(Acari: Ixodidae) WithBorrelia burgdorferi

Abstract

The abiotic and biotic factors that govern the spatial distribution of Lyme disease vectors are poorly understood. This study addressed the influence of abiotic and biotic environmental variables on Ixodes pacificus Cooley & Kohls (Acari:Ixodidae) nymphs, because it is the primary vector of Borrelia burgdorferi Johnson, Schmidt, Hyde, Steigerwaldt & Brenner in the far-western United States. Three metrics of Lyme disease risk were evaluated: the density of nymphs, the density of infected nymphs, and the nymphal infection prevalence. This study sampled randomly located plots in oak (Quercus spp.) woodland habitat in Sonoma County, CA. Each plot was drag-sampled for nymphal ticks and tested for B. burgdorferi infection. Path analysis was used to evaluate the direct and indirect relationship between topographic, forest structure and microclimatic variables on ticks. Significant negative correlations were found between maximum temperature in the dry season and the density of infected ticks in 2006 and tick density in 2007, but we did not find a significant relationship with nymphal infection prevalence in either year. Tick density and infected tick density had an indirect, positive correlation with elevation, mediated through temperature. This study found that in certain years but not others, temperature maxima in the dry season may constrain the density and density of infected I. pacificus nymphs. In other years, biotic or stochastic factors may play a more important role in determining tick density.

Truncated seasonal activity patterns of the western blacklegged tick (Ixodes pacificus) in central and southern California

“…high temperatures and low humidity), and avoid such conditions by entering states of inactivity or behavioral diapause (Needham and Teel, 1991;Padgett and Lane, 2001). I. pacificus, which spends >90% of its three year life cycle off-host, has been found to be particularly susceptible to high temperatures and low humidity and precipitation, which likely drive seasonal activity patterns of this tick (Eisen et al, 2002(Eisen et al, , 2003Padgett and Lane, 2001;Swei et al, 2011). Thus, while the variation in patterns of seasonal activity between the sites sampled in northwestern and southern California may be due to interannual differences in weather and abiotic conditions (Figs.…”

Comparative genetic diversity of Lyme disease bacteria in Northern Californian ticks and their vertebrate hosts

“…Sampling in Marin (Swei et al, 2011a). Sampled sites were in oak woodland habitat and chosen from a mixture of randomly selected plots (Meentemeyer et al, 2008).…”

“…Sampled sites were in oak woodland habitat and chosen from a mixture of randomly selected plots (Meentemeyer et al, 2008). All ticks were collected by drag sampling using a 1 m 2 white flannel cloth attached to a wooden dowel (Swei et al, 2011a). Drag cloths were checked every 15 m and all attached ticks were removed and stored in 70% ethanol for lab identification and DNA extraction.…”

“…infections in ticks from Marin and Sonoma Counties separately because these sites were separated by over 100 km and the plot designs were different between the two counties (Swei et al, 2011a(Swei et al, , 2012. The distribution of haplotype diversity identified from vertebrates sampled was also calculated for the two species with the highest sample sizes, N. fuscipes and P. maniculatus.…”

Lyme disease risk in southern California: abiotic and environmental drivers of Ixodes pacificus (Acari: Ixodidae) density and infection prevalence with Borrelia burgdorferi

“…), both key elements of entomological risk of human infection [10–12]. Within oak woodland habitats, temperature - particularly maximum summer temperatures - relative humidity, elevation, aspect and presence of dense leaf litter have been found to be important predictors of tick density and/or infection prevalence [13–15]. These associations suggest that a combination of direct, e.g.…”