Exposure level to Borrelia based on woodland type and temperature

Excerpt:

In the far-western United States, the nymphal stage of the
western black-legged tick, Ixodes pacificus, has been implicated
as the primary vector to humans of Borrelia burgdorferi sensu
stricto (hereinafter referred to as B. burgdorferi), the
causative agent of Lyme borreliosis in North America. In the
present study, we sought to determine if infection prevalence
with B. burgdorferi in I.
pacificus nymphs and the density of infected nymphs differ
between dense-woodland types within Mendocino County, California,
and to develop and evaluate a spatially-explicit model for
density of infected nymphs in dense woodlands within this
high-incidence area for Lyme borreliosis. In total, 4.9%
(264) of 5431 I. pacificus nymphs tested for the presence of B.
burgdorferi were infected. Among the 78 sampling sites, infection
prevalence ranged from 0 to 22% and density of infected nymphs
from 0 to 2.04 per 100 m(2). Infection prevalence was highest in
woodlands dominated by hardwoods (6.2%) and lowest for redwood
(1.9%) and coastal pine (0%). Density of infected nymphs also was
higher in hardwood-dominated woodlands than in conifer-dominated
ones that included redwood or pine. Our spatial risk model, which
yielded an overall accuracy of 85%, indicated that warmer areas
with less variation between maximum and minimum monthly water
vapor in the air were more likely to include woodlands with
elevated acarological risk of exposure to infected nymphs. We
found that 37% of dense woodlands in the county were predicted to
pose an elevated risk of exposure to infected nymphs, and that
94% of the dense-woodland areas that were predicted to harbor
elevated densities of infected nymphs were located on
privately-owned land.