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

J.P.

B.

the

Ixodes B. G.

RAHAN,

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control

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L.

and

1989.

Ray

Health

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versity

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Winstead.

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Lyme

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mice

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57:

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State

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BARBOUR,

GRUNWALDT,

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Borrelia burgdorferi infection in white-footed mice (Peromyscus leucopus) in hemlock (Tsuga canadensis) habitat in western Pennsylvania.

White-footed mice (Peromyscus leucopus) were captured and their tissues sampled from 27 sites in seven counties of western Pennsylvania in 1990 for is...
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