BORRELIA BURGDORFERI INFECTION IN WHITE-FOOTED MICE (PEROMYSCUS LEUCOPUS) IN HEMLOCK (TSUGA CANADENSIS) HABITAT IN WESTERN PENNSYLVANIA Author(s): Rexford D. Lord, Jan G. Humphreys, Veronica R. Lord, Robert G. McLean, and Curtis L. Garland Source: Journal of Wildlife Diseases, 28(3):364-368. Published By: Wildlife Disease Association DOI: http://dx.doi.org/10.7589/0090-3558-28.3.364 URL: http://www.bioone.org/doi/full/10.7589/0090-3558-28.3.364
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of Wildlife
Journal
BORRELIA
BURGDORFERI
(PEROMYSCUS HABITAT
INFECTION
LEUCOPUS)
IN WESTERN
Diseases, © Wildlife
28(3),
IN WHITE-FOOTED
IN HEMLOCK
(TSUGA
1992,
Disease
364-368
pp.
1992
Association
MICE
CANADENSIS)
PENNSYLVANIA
Rexford D. Lord, Jan G. Humphreys, Veronica R. Lord,2 Robert G. McLean,3 and Curtis L. Garland Department of Biology, Indiana University of Pennsylvania, Indiana, Pennsylvania 15705, USA 2Bwcellosis Laboratory, Institute of Veterinary Medicine, 2102 Maracay, Venezuela Division of Vector-borne Infectious Diseases, Center for Infectious Diseases, Centers for Disease Control, U.S. Public Health Service, Department of Health and Human Services, Box 2087, Fort Collins, Colorado 80522,
White-footed
ABSTRACT: from
sites
27
in
seven
mice counties
(Peromyscus of
leucopus)
western
were
Pennsylvania
captured
1990
in
for
and
their
isolation
tissues
and
USA
sampled
identification
of
Borrelia burgdorferi. Two hundred sixty mice were captured from which there were 27 isolations. Significantly more mice were captured and significantly more isolations made from hemlock (Tsuga canadensis) habitat than from deciduous species forest. Hemlock habitat is sparse and focal but evidently increases winter survival of mice, and thus possibly results in increased infection rates in mice. Key words: Borrelia burgdorferi, white-footed mice, field sampling, hemlock, habitat prevalence, Peromyscus leucopus, Tsuga canadensis. INTRODUCTION
The involvement of (Peromyscus leucopus) of the Lyme borreliosis burgdorferi been amply 1984; Levine 1987a,
b;
Donahue
et
Ixodes
dammini
has
been
repeatedly
al., 1983; 1985). The
white-footed mice as reservoir hosts agent Borrelia
(Burgdorfer demonstrated et a!., 1985;
tick
principal northeastern
Pennsylvania
vector
importance
to
be
the spirochete in States (Anderson
et al.,
1983;
of
agent of Lyme evenly distributed ious ecosystems,
et a!., 1979)
confirmed
of United
Bosler
a!., 1982) has (Bosler et a!., Anderson et a!., 1987). The deer
(Spielman
Levine
the the et
monstrable rates
et a!.,
white-tailed
cases region
1989).
The
reported of the
are state
majority from the although
cases have been reported from counties (Brittingham, 1989). known about the natural reservoir tick vectors in Pennsylvania. A premise of this study was
et
al.,
(Steere,
of the human southeastern
deer
borreliosis throughout and this
through
of
mammal
in
that
would all would
differential hosts
western Little is hosts or
infection different
habi-
tats. Another mals, always
premise was that small the most abundant,
prove
indicators.
useful
Thus,
the
of the study was to sample different itats by trapping the small mammal cies and to determine which species
1984; 1985).
burgdorferi.
revealed
density of white-footed mice and its role in the epizootiology of this disease is known in New England (Anderson et al., 1987a; Mather
et a!.,
1989)
attention elsewhere. Lyme borreliosis ward from the New
but
has
received
has expanded England states
New York and New Jersey decade and has become
during the established
the
habitat
MATERIALS
To study tions
less
in
the
the
role
enzootiology
best
suited
mamwould purpose
(Odocoileus virginianus) in maintaining I. dammini tick populations and to the incidence of Lyme borreliosis is well documented (Main et al., 1981; Bosler et al., Magnarelli et a!., 1984; Wilson et a!., To a certain extent, the population
the
be unthe varbe de-
habspebest for
B.
AND METHODS
of small of
mammal Lyme
populaborreliosis
knowledge of an area already known to contain the disease. Reports of a higher than usual number of human cases in the city of St. Marys, Elk County (41#{176}29’N,78#{176}31’W), in western Pennsylvania suggested the possible presence of an endemic focus in that area. Lack of precisely where in Elk County persons were required
westand last in 364
LORD ET AL.-BORRELIOSIS
being
infected
pecting”
and
led to an initial B. burgdorferi in
for
other
small
mammals
period
of “pros-
around
the
city
TABLE
365
MICE
1. Capture of white-footed mice and isolaof Borrella burgdorferl spirochetes in western
mice
tion
of St.
Pennsylvania,
white-footed
IN WHfl’E’FOOIED
1990.
Marys.
A trap (30 x 7.6 x 7.6 cm, Sherman live trap) small mammals was selected to sample any species up to a small squirrel in size. The bait selected (peanut butter) attracts all small rodents and shrews. Forty traps (wrapped in several layers of newspaper and supplied with cotton for protection against the cold) were set 18 February 1990 (Table 1) and recovered the follow-
day.
ing
5 km
Ten
each
traps
were
to the
north,
set at a distance south,
east
of about and
west
of
the city. Traps were set at 10-m intervals in a line and when possible were placed next to fallen tree trunks. They were placed in exactly the same pattern in all habitats (hemlock or deciduous forest). Initial placement
and subsequent findings guided later of traps in diverse habitats. Habitats
sampled
included
valleys
along
forest
hemlock
clumps
and
streams
located
softwood
legheny
Plateau
hickory) occasion
with well drained topography. traps were set for one night
the end of 1983) were
the
trapping
(bladder
Tissues captured
were
BSK
lated in cubated
at 34
C.
Later using a
examined
positive
4 days
2 to
samples
On each only. At
(Lord, determine various habitats from
removed,
triturated
from
darkfield a month.
passed
inocuand in-
the tubes microscope, at
samples for
were
mammals
1984), then 7 ml of BSK
(Barbour, containing
(oak,
boards
spleen)
aseptically
tubes
of
forests
results.
and
medium
intervals
hardwood
the study, tracking used to independently sp. activity in the
Peromyscus to confirm
were
were
to other
Spirochete
BSK tubes
and slides were prepared for fluorescent antibody (FA) examination. A drop of culture was air dried on a slide, fixed in cold acetone for 10 mm, dried and stored at 20 C. In preparation
for
FA examination,
a drop
of fluorescein-con-
jugated rabbit anti-Borrelia burgdorferl IgG (Centers for Disease Control, Fort Collins, Colorado 80522, USA) was placed on the dried preparation and incubated at 25 C in a moist, dark chamber for 30 mm. The slide was shaken to remove conjugate, immersed in distilled water for 10 mm, air dried, covered with a drop of 10% glycerine in water and a cover slip, and
examined Bladder
using and
a fluorescence ear
tissues
microscope.
taken
from
mice
cap-
tured in March (Table 1) were tested (Schwan et al., 1988), the results of which led to subsequent sampling of ears only (Sinsky and Piesman,
1989).
from
anesthetized
Approximately mice
one was
County
February
Elk
11/40
March
Elk
27/60 19/80
Isolates 1 11
April
Elk
June
Clearfield
July
Elk
11/72
1
August
Elk
3/32
1
September
Elk
63/150
1
September
Westmoreland
18/60
September
Cameron
11/40
October
Elk
38/90
October
Jefferson
1
6/48
4
5/10
November
Indiana
November
Somerset
November
Cambria
Total
7 counties
56/120
7
6/20 3/10 260/842
27
deciduous
(aspen, red maple) also in valleys along Hillside slopes and the top of the Al-
streams.
in
in
capture! Trap-nights
Mice
Month
for
third
severed
of the
with
ear
scis-
dipped in 70% ethyl alcohol, placed liquid bleach for 10 mm, then dipped in again and flamed before being placed ml of BSK media in a plastic tube. The was then triturated in the tube with a
in 10%
sors,
alcohol in 0.05
sample broken glass rod, 0.02 ml of the suspension passed to a tube with 7 ml of BSK, and processed as previously stated. Representative isolates were
shipped to the CDC Laboratory (Fort Collins, Colorado) where they were confirmed as being B. burgdorferi by the indirect FA test using antiOspA monoclonal al., 1986) with
antibodies H5322 (Barbour et known strains of B. burgdorferi B. hermsll as positive and negative
(B-Si) and controls. The isolates were placed in the CDC Borrell.a spp. reference collection (PA91-480 through PA91-488). Ticks were captured by flagging or from mice as corollary to the small mammal studies. Ticks were identified, then dissected and suspensions of midgut examined scope. Positive samples
using a darkfield were confirmed
as described previously. The Chi square and Fisher’s Exact used to statistically analyze the data.
microby FA
tests
were
RESULTS
Table 1 lists the months, counties, mice captured, traps set and isolates made. In the traps, white-footed mice prevailed numerically, backed
but voles
three southern volans), three
we also captured (Clethrionomys
two redgapperi),
flying squirrels (Glaucomys short-tailed shrews (Blarina
366
JOURNAL OF WILDLIFE DISEASES, VOL. 28, NO. 3, JULY 1992
brevicauda),
and
(Tamiasciurus Two
were
white-footed
in 842
in the field for
=
one
night
were
mixed
rates
itats
between
while
only
In
and
four (10%)
were
53 mice
were
were
in hemlock, trapped
in deciduous
habitat, but captured
the
5.65, P = and October) 58 trap-nights (40%) =
in deciduous forest in 205 trap-nights
(38%) (difference not significant, x2 = 0.04). To reconfirm the high trapping success in hemlock habitat, at the end of April, 10 traps
were
set
(five
each)
in two
hemlock
sites west of St. Marys, and 10 traps were placed in deciduous forest between the two hemlock sites. Likewise 20 tracking boards were placed in the same pattern (traps and boards
at
10-m
intervals
in a line)
in both
habitats. Five mice were captured in the hemlock habitat and two in the deciduous forest. In like manner, the tracking boards reflected the difference; six of 10 boards were positive for Peromyscus sp. in hemlock
habitat,
but
only
one
of 10 boards
was
positive Mice and on
from the deciduous were trapped in top of the Allegheny
capture in 564 mice in of the (21%).
rate in the valleys was 199 mice trap-nights (35%), on hillsides 43 193 trap-nights (22%), and on top plateau 18 mice in 85 trap-nights The effect of topography on the
capture
rate
was
3.14, P
significantly
forest site. valleys, hillsides Plateau. The
different
(x2
=
0.08) for the capture
valleys
and
the
Twenty-seven were made from the
entire
from was lates
22
taken were
deciduous significant were from
in valleys, from
rate
were
=
from
158
habitat, 102 mice
while (5%)
and the difference 3.65, P = 0.05). Iso24 of 199 mice (12%) taken =
one and
of 43 mice from
from the top the difference no
valleys
be-
5.65, P hillsides (x2 = 0.00).
forest
from
showed
=
made
in hemlock made from
(x2
hillsides,
(11%) taken Analysis of
and
isolates of B. burgdorferi white-footed mice during
study;
mice (14%) five isolates
rate be-
plateau,
tween valleys and hillsides (x2 0.02), but the difference between and plateaus was not significant
between
in 40
forest;
(x2
difference was significant 0.02). In fall (September mice were taken in 145 in hemlock
haband
(38%)
mice
(TsuCap-
these two late winter
March),
trap-nights
trap-nights
77 mice
sam-
(hardwoods
between seasons.
in 140
Jefwere and In(Table
habitats
deciduous
(February
taken
Indiana,
forests and hemlock with deciduous trees.
varied
trap
counties
Westmoreland) sites in Elk repeatedly
different
and softwoods) ga canadensis) ture
seven E!k,
and some sampled
markedly
(one
1 trap night).
=
in
Clearfield,
ferson, Somerset, sampled, with diana counties 1).
mice
trap-nights
sites
(Cameron,
spring
squirrels
tween
sixty
captured
Two
red
hudsonicus).
hundred
Twenty-seven
pled
three
of
of the in the
difference and
(2%)
two
(OR
plateaus,
but
taken
18
mice
plateau. isolation 0.91)
=
the
dif-
ference between valleys and hillsides was significant (OR = 0.17, P = 0.09). Five isolations of B. burgdorferi were made from I. dammini ticks; three were from adults and two were from nymphs (15% of 34 adults and nymphs). All isolations from ticks came from the region 5 km W of St. Marys, and all were from collections made by flagging in May. All of these isolations were from the valley with three from deciduous forest and two from
hemlock
habitat. DISCUSSION
In late winter, more mice were captured in hemlock habitat than in deciduous forest
habitat.
rates in indicating deciduous
However,
by
fall
the
the difference. vival of mice
Conversely, the in the hemlock
winter habitat
pears to have been superior. The hemlock provide a reliable source for food for the mice throughout ter, loss and the
and the through reduce wind Isolation
hemlock
capture
these two habitats were similar, that summer reproduction in forest habitat compensated for surap-
cones of of seeds the win-
trees provide cover from heat radiation during cold nights, wind velocity, thus reducing
chill factor. rates also habitat
than
were
greater
in the
deciduous
in
the for-
LORD
est. Possibly in hemlock ability
the increased results in an
of
infected
nymphal ticks mer, increasing mice. The (February
survival increased
mice
during the
for
of
of mice avail-
larval
the spring transmission
AL.-BORRELIOSIS
Borrella
mice
and sumto other
in the Elk County
are severe with little chance before early May. Those made from mice captured frozen This
ground. study
detecting
indicates
through sampling ter finding a high in mice
from
we
gave
in
low sults
incidence indicate
attention
aiding
binds and
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