Sunday, July 17, 2005

Hi Mtn. rodent live-trapping research

Hi all,
Dr. Larisa Vredevoe, professor in the Cal Poly Bio. Sci. Dept., and her
students are conducting research using Hi Mountain Lookout as a field
laboratory station. This past weekend 8 rodents were live-trapped- an
unepected low capture rate from the 64 live traps set out the night
before- and processed at the lookout ‘laboratory’ for a study on the
central coast to determine the prevalance of rodent populations as
resevoir hosts for the Lyme disease bacteria (genus Borrelia).
Following are selected excerpts of an abstract, introduction and some of
the methodology from Dr. Vredevoe’s previous technical publication from
a similar research project. Hi Mountain may be added as another study
site to this research project depending on whether or not the Borrelia
bacteria are isolated from the rodents captured up there.
The ongoing condor radio tracking efforts at the lookout, Cal Poly
student field research projects, and this rodent/ Lyme disease study are
examples of how the Hi Mountain Lookout Project continues to function
importantly as a biological field research station.
Steve Schubert
PS- To view the photos I took of the rodents being processed at Hi Mtn.
Lookout and then being released, go to the yahoo photo album link. I
find it works best to click on and enlarge the first thumbnail photo and
then click the ‘view slideshow’ function.
Excerpts from published article:
Detection and Characterization of Borrelia bissettii in Rodents from the
Central California Coast
Department of Biological Sciences, California Polytechnic State
University, San Luis Obispo, CA 93407
J. Med. Entomol. 41(4): 736Ð745 (2004)
ABSTRACT This is the first report of Borrelia burgdorferi sensu lato in
rodents from San Luis Obispo county, with most isolates obtained from a
previously unreported host, Neotoma lepida Thomas.
B. burgdorferi sensu lato was identified in seven rodent species,
including the California vole, Microtus californicus Peale; dusky-footed
woodrat, Neotoma fuscipes Baird; desert woodrat, Neotoma lepida Thomas;
brush mouse, Peromyscus boylii Baird; California mouse, Peromyscus
californicus Gambel; deer mouse, Peromyscus maniculatus Wagner; and
western harvest mouse, Reithrodontomys megalotis Baird.
Ear punch biopsies were cultured in BSK-H medium from 179 rodents
trapped at six different study sites. Overall, prevalence of rodent
infection was 44/179 (24.6%), with 34 of these isolates from
N. lepida. Spirochete isolates were obtained from rodents at all
studysites, indicating widespread prevalence of B. burgdorferi sensu
lato across rodent species and habitats. Nucleotide sequences for 14 of
these isolates have been submitted to GenBank. Isolates from three N.
lepida and one P. boylii had identical flagellin gene sequences, and
phylogenetic analysis placed these spirochetes in B. burgdorferi sensu
lato group DN127, now known as B. bissettii Postic, Marti Ras, Lane,
Hendson &
Baranton. Additional sequencing of the intergenic spacer regions between
the 5S and 23S ribosomal genes was performed on three of these isolates.
Phylogenetic analysis separated these isolates into two
clusters that grouped with Colorado or California isolates. The role of
B. bissettii and related species other than B. burgdorferi sensu stricto
Johnson, Schmid, Hyde, Steigerwalt & Brenner as human pathogens in the
United States warrants further investigation.
KEY WORDS Lyme disease, Borrelia bissettii, Borrelia burgdorferi,
Ixodes, rodent
OVER THE PAST 10 YEARS, northern California has been recognized as a
rapidly developing focus of several
tick-transmitted bacteria, particularly the Lyme disease spirochete,
Borrelia burgdorferi, and the rickettsial
agent of human granulocytic ehrlichiosis,
Anaplasma phagocytophilum (Dumler et al. 2001); foci are predominantly
in several northwestern counties of the state (Burgdorfer et al. 1985,
Clover and Lane
1995, Fritz et al. 1997, Foleyet al. 1999, Kramer et al. 1999, Lane et
al. 2001, Holden et al. 2003). The situation
in other regions of California, representing a tremendous diversity of
ecosystems, remains poorly understood. In particular, an increasingly
complex picture of B. burgdorferi sensu lato (s.l.) ecology
throughout the United States has emerged as substantial genetic
heterogeneity among California and other North American isolates from
diverse tick and mammalian reservoir hosts continues to be recognized
(Mathiesen et al. 1997, Postic et al. 1998, Lin et al. 2002). In San
Luis Obispo Countyand other areas of the central California coast, the
B. burgdorferi s.l. genospecies diversity and enzootic maintenance of
these agents have remained largely unstudied.
Eleven Borrelia genospecies have been described within the B.
burgdorferi s.l. complex. In the United States, three of these
genospecies have been identified,
including Borrelia andersonii (Assous et al. 1994, Postic et al. 1994,
Marconi et al. 1995), Borrelia bissettii (Assous et al. 1994, Postic et
al. 1994, Postic et al. 1998), and B. burgdorferi sensu stricto (s.s.)
Johnson, Schmid, Hyde, Steigerwalt & Brenner (Baranton et al. 1992).
Only B. burgdorferi s.s. seems responsible for classic human Lyme
disease in the United States. In Northern California, nidicolous ticks,
primarily Ixodes spinipalpis Hadwen & Nuttall (I. neotomae; Norris et
1997a), transmit B. burgdorferi s.s. between rodent reservoir hosts such
as dusky-footed wood rats, Neotoma fuscipes Baird, whereas western
blacklegged ticks, Ixodes pacificus Cooley& Kohls, may transmit
the organism from rodents to humans (Brown and Lane 1992). At least one
other species of Borrelia in this group also exists in California. B.
burgdorferi s.l.
group DN127 was redescribed as B. bissettii sp. nov. based on
differences in OspA and OspB proteins (Bissett
and Hill 1987, Postic et al. 1998). B. bissettii was first described
from I. pacificus in California but has
subsequentlybeen found in other parts of the United States and Europe.
Experimentally confirmed tick vectors of B. bissettii include I.
spinipalpis and I. pacificus in the western United States (Burkot et al.
2000, Eisen et al. 2003) and I. scapularis in the eastern United States
for B. burgdorferi strain MI-6 (Sanders and Oliver 1995), which was
later recharacterized as B. bissettii (Lin et al. 2001). The
pathogenicity of B. bissettii to humans in the United States is not
known, although European strains have been isolated from humans
displaying clinical symptoms associated with Lyme borreliosis (Picken et
al. 1996, Strle et al. 1997).
In this study, we investigated the ecology and genetic heterogeneity of
B. burgdorferi s.l. on the central California coast compared with other
parts of California and the United States. Here, we provide evidence for
the previously undocumented widespread prevalence of B. burgdorferi s.l.
among San Luis Obispo county rodent populations from a variety of
Materials and Methods
Study Sites. To evaluate the presence of B. burgdorferi s.l. in San Luis
Obispo between August 2001 and February2003, we selected six study sites
a variety of habitats with diverse rodent populations. San Luis Obispo
is16 km from the ocean on the central California coast, midway between
San Francisco and Los Angeles. We selected study sites
with moderate-to-heavy human use to later assess human risk of contact
with any discovered tick-borne agents. Two study sites were located in
Poly Canyon,
on the northeastern edge of the California Polytechnic State University
campus. Natural vegetation in this region includes chaparral, coastal
scrub, grassland,
coastal live oak woodland, and riparian woodland. The hillsides consist
of rocky
outcrops, coastal and yucca scrub, chaparral, and coastal live oak
woodland,with grassland dominating the rolling hills. The lower Poly
Canyon study site included two distinct habitats in
which traps were set, riparian woodland with a stream running through
the site and yucca scrub on a rocky slope. Traps were set at the upper
Poly Canyon site in
both live oak woodland and a mixed habitat containing both coastal and
yucca scrub. The third study site was
located at Pennington Creek Biological Preserve, 81 ha of land located
13km northwest of the Cal Poly campus. Vegetation at this site was
similar to that of lower Poly Canyon but was less disturbed by human
activity. Montana de Oro state park is located near Los Osos, 19 km
southwest of San Luis Obispo. Vegetation at the study site included
coastal sage scrub, chaparral, and riparian woodland communities, but
traps were placed almost exclusivelyin riparian
woodland. Cerro San Luis, with an elevation of 394 m, is located in the
center of San Luis Obispo. The study
site was located at the base of the mountain in a habitat predominated
by prickly pear cacti and coastal scrub. The sixth study site was Laguna
Lake park, located at the eastern end of the Los Osos valley on the edge
of San Luis Obispo. Natural vegetation
communities at this site include freshwater marsh, riparian woodland,
serpentine springs, and several
types of grassland. Traps were placed exclusively in the serpentine
grassland habitat at this site.
Rodent Trapping and Sample Collection. We identified several homogeneous
vegetation communities within each study site to set trapping grids. Two
or three 4 by 4 trapping grids were set at each site, with two traps
placed at each station. Stations were spaced 10 m apart, with a total of
64 Ð96 traps set per trapping night. Rodents were live-trapped in
Sherman XLK traps (Tallahassee, FL) baited with rolled oats over two
trapping nights in August, October, and November
2001; January, April, and November 2002; and February 2003. Captured
rodents were identified (Jameson and Peters 1988), weighed, and sedated
an i.p. injection of ketamine/valium (30 mg/kg:5 mg/kg). After sedation,
rodents were sexed, ear-tagged with a uniquely numbered tag (National
Band and
Tag, Newport, KY) to facilitate recapture identification,attached ticks
removed and retained for identification, and two 2Ð4-mm ear biopsies
were taken
from the outer margin of each ear with a sterile scalpel. One ear sample
from each rodent was frozen at20C in 1.5-ml centrifuge tubes. The second
ear sample was placed in sterile phosphate-buffered saline for several
hours until it was prepared for spirochete culture.
After recovery from anesthesia, all rodents were returned to their
capture station and released. Rodents
recaptured the following trapping night were immediately released at the
point of capture without resampling. Those animals recaptured during a
later trapping
date were resampled to gauge whether infection status might change over
the course of the study.