ecological aspects of distribution of the population of ixodes ricinus

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DISTRIBUTION-OF-I.-RICINUS-AND-INFECTION-WITH-B.-BURGDORFERI
Zoologica
Poloniae (2004) 49/1-4: 77-84
77
ECOLOGICAL ASPECTS OF DISTRIBUTION
OF THE POPULATION OF IXODES RICINUS
AND THEIR INFECTION WITH BORRELIA BURGDORFERI
IN WESTERN POMERANIA (NW POLAND)
M IROS£AWA H UMICZEWSKA
Department of Human Ecology University of Szczecin. Piastów 30 B,
70-065 Szczecin
Abstract. In 2000-2002, the ticks (Ixodes ricinus) were collected, by flagging,
in forested areas of the Szczecin, Iñsko, Drawsko, and River S³upia Landscape Parks
in Western Pomerania. The ticks were collected in April - October each year, once a
month, between 10.00 and 16.00 hours, each time in the same sites. The sites were
located near lakes or streams. Seasonal activity of the ticks was determined by calculating the abundance of larvae, nymphs, and adults (males and females) in each collection event. During the three seasons of study, a total of 19646 tick individuals were
collected; the larvae, nymphs, and adults constituted 12.9%, 62.4%; and 24.6% individuals, respectively. The landscape parks differed in the tick abundance. Most ticks
(6425 individuals) were collected in the Drawsko Landscape Park, the collection showing a substantial predomination of nymphs which accounted for 75% of all individuals,
the proportion of larvae and adult being almost identical (about 12% each). On the
other hand, the smallest collection was obtained in the River S³upia Valley Landscape
Park. Nymphs accounted for less than a half (about 47%) of the collection; adults
formed almost one-third, i.e., 28.6%, while larvae constituted 23.8%. The Iñsko Landscape Park's collection was quite large. The collection was dominated by nymphs
(60%), followed by adults (30%) and larvae (as little as 10%). The Szczecin Landscape
Park yielded a somewhat smaller collection dominated by nymphs (almost 60 %),
followed by adults (about 30%). The parks and sites differed in the seasonal activity
of the ticks. Usually, however, two activity peaks could be observed each year: in
spring and in late summer. The average abundance of the tick population, as determined
for the entire collection, was high (18.9 individuals/100 m 2 ). Individual sites, however,
differed in the tick abundance which varied from 10 to 35 individuals/100 m 2 . The
spirochetes B. burgdorferi were found in 4337 specimens e. c. 22.1% whole population.
The number infected larvae was 496 (19.3%, nymphs 2673 (21.8%), adults 1168 (24.1%).
X V I I I C o n g r e s s o f P o l i s h Z o o l o g i c a l S o c i e t y, 1 5 - 1 8 S e p t e m b e r 2 0 0 3 , To r u ñ , P o l a n d
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INTRODUCTION
The ticks Ixodes ricinus are very important vectors of numerous pathogens: bacteria, rickets, viruses, and protozoans. For this reason they are in the
focus of attention of not only zoologists and parasitologists, but also epidemiologists and bacteriologists in various geographical regions. Recently, there has
been an increase in the amount of attention paid to ticks as they are vectors
for the spirochete Borrelia burgdorferi. Consequently, numerous researchers in
Poland and world-wide are engaged in studies on dispersal and seasonal activity of I. ricinus and on the extent of their infestation with B. burgdorferi (G REY
et al., 1992; TALLEKLINT et al., 1993; 1996; HUMICZEWSKA, 1995; 2001; HUMICZEWSKA
et al., 1997; 2003; O`C ONNEL et al., 1998; H UBALEK et al., 1998; N ILLSON , 1998;
N OWOSAD et al., 1999).
Earlier studies (HUMICZEWSKA et al., 1997; 2003) on dispersal of I. ricinus
in woodlands of Western Pomerania showed there to be a real risk of tick
infestation of humans, hence a potential danger of a B. burgdorferi infection.
The intensity of transmission of the spirochete and its dispersal are diverse
processes which depend largely on climatic and phenological factors (M AMATEAU
et al., 1998). In their environmental study carried out in Sweden, TALLEKLINT et
al., (1996) demonstrated Borrelia infection dynamics to be highly seasonal.
Moreover, it is very probable that human infestation with ticks increases with
increasing human population density. With those findings in mind, changes in
tick abundance were followed in areas surrounding lakes; such areas support
mass tourism in summer, for which reason the potential exposure to ticks increases greatly. Abiotic factors affecting tick distribution, i.e., temperature and
humidity of tick habitats surveyed, were taken into consideration as well.
MATERIALS AND METHODS
The ticks I. ricinus were sampled in forested areas the Szczecin, Iñsko,
Drawsko, and River S³upia Valley Landscape Parks in Western Pomerania. The
ticks were collected by flagging, i.e., sweeping the forest litter, understorey, and
shrubs, up to 80 cm above ground, with a flannel cloth. The collections were
made once a month, in April-October 2000-2002, between 10.00 and 16,00 hours,
from the same pre-set sites. The collection sites were located in areas adjacent
to lakes or streams. On each collection event, air temperature and humidity was
measured with a hygrometer. Seasonal activity of ticks was determined by calculating abundance of larvae, nymphs, and adults (males and females) per collection event.
Characteristics of tick collection sites. The ticks were collected from shores
of lakes located within Western Pomeranian landscape parks: the Binowskie,
Glinno, and Szmaragdowe in the Szczecin Landscape Park; the Iñsko, Wisola,
Krzemieñ, Okole, and D³usko in the Iñsko Landscape Park; the Drawskie, Wilczkowo,
Prosino, £ubie, and Komorze in the Drawsko Landscape Park, and the Strzegomino,
Sitno, G³êbokie, Krzynia, and D³ugie in the River S³upia Valley. Collecting sites
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DISTRIBUTION-OF-I.-RICINUS-AND-INFECTION-WITH-B.-BURGDORFERI
79
were situated on forested lake shores, visited by tourists and sunbathers. The
woodlands surrounding the lakes are mixed forests dominated by alder, oak, and
beech, with a slight admixture of pine only; the shrub level and the understorey
are both well developed.
The extent of I. ricinus infection with B. burgdorferi was evaluated with
the polymerase chain reaction (PCR), a specific DNA amplification technique,
using B. burgdorferi sensu lato-specific primers. Amplification was carried out
in a Mastercycler thermocycler, with BOR1 and BOR2 starters. PCR product
electrophoresis was conducted in 3% agarose gel. Reaction products were detected
by hybridisation with the DNA probe. Each control consisted of a positive and
a negative control.
RESULTS AND DISCUSSION
The results of tick collections in 2000-2002 are shown in Table 1. During
the three vegetation seasons, a total of 19646 ticks were collected. The collection was dominated by nymphs (12240, 62.3%), followed by adults (4840, 24.6%),
larvae being the least numerous (2566, 13.1%) (Table 2). The parks differed in
the abundance of ticks (Table 1). The highest number of ticks (6425) was collected in the Drawsko Landscape Park, the collection being clearly dominated
by nymphs (75% of all individuals); adults and larvae were almost equally
numerous (12.7 and 12.8%, respectively) (Table 1). The smallest collection (3823
individuals) was obtained from the River S³upia Valley Landscape Park. Nymphs
accounted for less than a half (47.6%), adults for almost 1/3 (28.6%), while
larvae constituted 23.8% (Table 1). The collection obtained from the Iñsko
Landscape Park was quite substantial: it consisted of 5230 individuals: 60%
nymphs and 30% adults, larvae contituting as little as 10% (Table 1). The
Szczecin Landscape Park yielded a somewhat smaller collection: 4168 individuals, including 1398 (33.5%) adults; amost 60% nymphs and larvae which were
the least numerous (6.8%) (Table 1).
Data on the tick abundance dynamics (Fig. 1, Tables 3-5) showed two
peaks of seasonal activity in 2000: in June and in September (Fig. 1, Table 3).
In 2001, a very high peak was observed in May, the abundance increasing
slightly again in September (Fig. 1, Table 4). In 2002, the population abundance
peaked in May, another pronounced peak being observed in September (Fig. 1,
Table 5). Each year, the population abundance was at its lowest in October. That
was related to the October temperature decrease to 10-12O C, the range seemingly
limiting the tick activity (Tables 3-5). In spring and summer, the abundance of
I. ricinus was affected by air humidity. The collection sites were the least humid
in July and August, the months yielding the lowest abundance. The relationships discussed are still more pronounced when the tick activity is compared
between the collection areas. The smallest collection was obtained from the
River S³upia Valley Landscape Park, with average humidity of less than 70%, the
largest collection being that from the Drawsko Landscape Park with average
humidity of 85%. On the other hand, the tick activity in different areas and at
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M.-HUMICZEWSKA
80
Table 1
Composition of population of Ixodes ricinus in Western Pomerania and extent
of infection Borrelia burgdorferi in three vegetation seasons
Collection area
Stage of
development
Individuals found
N
%
Infected individuals
N
%
Drawsko Landscape Park
Larvae
Nymphs
Adults
T O TA L
0815
2484
1398
6425
012.7
074.5
012.8
100.0
0284
0066
0284
1584
23.2
22.9
27.9
24.6
Iñsko Landscape Park
Larvae
Nymphs
Adults
T O TA L
0571
0391
0391
5230
010.6
060.2
029.2
100.0
0815
4788
0822
1147
26.3
20.6
23.0
21.9
The River S³upia
Valley Landscape Park
Larvae
Nymphs
Adults
T O TA L
0815
0557
3146
3825
023.8
047.6
028.6
100.0
1527
0147
0649
0578
13.2
15.0
16.8
15.1
Szczecin Landscape Park
Larvae
Nymphs
Adults
T O TA L
0284
2484
0571
4166
006.8
059.6
033.5
100.0
2484
0476
1398
0933
23.2
19.1
27.9
22.4
Table 2
Abundance of individual developmental stages of Ixodes ricinus and the extent of their
infection with Borrelia burgdorferi in the Pomeranian Lake District in 2000-2002
Developmental stag
Larvae
Nymphs
Adults
T O TA L
Number and percentage of
individuals collected
02566
12240
4840
19646
013.1
062.3
024.6
100.0
%
%
%
%
Number and percentage of
individuals infected
0496
002673
01168
4337
19.3
21.8
24.1
22.1
%
%
%
%
various collection sites varied in each year. Usually, however, two activity peaks
were observed. For example, on Lake £ubie in the Drawsko Landscape Park, the
year 2001 was characteristic by showing a very pronounced peak in May and
another small peak in August, while a single peak, in June, occurred in 2002. In
contrast, on Lake Glinno in the Szczecin Landscape Park, as many as three peaks
were observed in 2002: the first, most pronounced, in May, followed by two
smaller peaks: in July and in August. Although two peaks of activity, in spring
and in summer, are usually observed in temperate climate, similar shifts in
activity were reported also by other authors (L ACHMAYER et al., 1977; H UBALEK
et al., 1991; G RAY et al., 1998; T ALLEKLINT and J AENSON , 1998; L INDGREN and
G USTAFSON , 2001). According to these authors, the timing of peaks depends on
many factors, such as temperature and humidity as well as vegetation cover,
terrain relief, and even the thickness of snow cover in winter.
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DISTRIBUTION-OF-I.-RICINUS-AND-INFECTION-WITH-B.-BURGDORFERI
81
Table 3
Seasonal activity of Ixodes ricinus in the Pomeranian Lake District in 2000
Number of ticks collected
Month
To t a l
Larvae
Nymphs
Adulds
Temperature ( OC)
Humidity (%)
May
June
July
August
September
October
1262
1620
0926
0847
1012
0519
199
155
139
153
111
0 58
0753
1049
0553
0508
0663
0307
0310
0416
0234
0186
0238
0160
18
17
19
20
16
12
85
87
87
75
85
85
T O TA L
6186
815
3827
1544
18
85
Table 4
Seasonal activity of Ixodes ricinus in the Pomeranian Lake District in 2001
Number of ticks collected
Month
To t a l
Larvae
Nymphs
Adulds
Temperature ( OC)
Humidity (%)
May
June
July
August
September
October
1803
1420
0998
1103
1356
5387
0252
0213
0139
0111
0178
0129
1191
0852
0680
0772
0880
0218
0360
0355
0179
0220
0298
0040
17
18
18
19
16
11
87
85
68
75
85
85
T O TA L
7067
1022
4593
1452
16
80
The average tick population density, as determined across the collections,
was high (19 individuals/100 m 2 ). The density, however, differed between sites,
from 10 inds/100 m 2 near Lake Binowo (Szczecin Landscape Park) to 35 inds/ 100
m 2 on Lake £ubie (Drawsko Landscape Park). A substantial temporal variability
was observed as well, from a mean of 16 inds/100 m 2 in May to 27 inds/100 m 2
in June, 26 inds/100 m 2 in July and August, 23 inds/100 m 2 in September, to as
few as 5 inds/100 m 2 in October.
Infected ticks occurred in all the collection sites, with the overall infection
incidence being 22.1%. The highest number of infected ticks (1892, i.e., more
than 40% of the entire collection) was collected in 2001. In 2000, the infected
ticks (1309) made up 30% of the collection; 136 infected ticks (26% of the
collection) were collected in 2002. Individual developmental stages of
I. ricinus differed in the prevalence of infection: the highest number of infected
individuals (24.1%) was detected among adults, while the infection affected
almost 22 and about 19% of nymphs and larvae, respectively.
The results obtained in this study are somewhat different from those
produced by research in other forested recreation areas in Poland where the
seasonal activity and B. burgdorferi infection of ticks were recorded. In the
recreational areas of the Tri-City (Gdansk, Gdynia, Sopot), B. burgdorferi were
present in 10.3% of the I. ricinus population (WEGNER et al., 1997), while NOWOSAD
et al., (1999) recorded B. burgdorferi in almost 18% of the tick population
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82
Table 4
Seasonal activity of Ixodes ricinus in the Pomeranian Lake District in 2002
Number of ticks collected
Month
To t a l
Larvae
Nymphs
Adulds
Temperature ( OC)
Humidity (%)
May
June
July
August
September
October
1697
1423
0908
0841
1317
0207
237
113
088
064
197
00
0978
0810
0637
0503
0762
0166
0482
0500
0186
0274
0358
0041
17
18
23
25
19
11
88
85
60
55
80
85
T O TA L
6393
699
3853
1841
19
75
2000
1800
1600
volume
wolume
1400
1200
1000
2000
800
2001
2002
600
400
200
0
may
june
july
august
september
october
m onth
Fig. 1. Seasonal activity of Ixodes ricinus in the Pomeranian Lake District in 2000-2002
studied in urban forests of Poznañ. Earlier studies (1996-1998) in woodlands of
Pomerania (H UMICZEWSKA et al., 1997; 1998) revealed a mean infection prevalence
of 14.5%. On the other hand, similar studies in water areas and forests of
Szczecin and its environs showed almost 28% of the tick population to be
infected by B. burgdorferi (H UMICZEWSKA , 2001). Considering the high extent of
tick infection demonstrated in this study, it can be concluded that lake shores
and the adjacent forest areas support tick populations that are infected to a
higher extent than those in other habitats. Consequently, the risk of humans
being attacked by ticks infected by B. burgdorferi in the areas studied is higher
than elsewhere.
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DISTRIBUTION-OF-I.-RICINUS-AND-INFECTION-WITH-B.-BURGDORFERI
83
EKOLOGICZNE UWARUNKOWANIA ROZMIESZCZENIA KLESZCZA
POSPOLITEGO IXODES RICINUS I ODSETEK ZAKA¯ENIA ICH
KRÊTKAMI BORRELIA BURGDORFERI NA POMORZU ZACHODNIM
STRESZCZENIE
Kleszcze Ixodes ricinus od³awiano na zalesionych terenach parków
krajobrazowych na Pojezierzu Pomorskim: Szczeciñskiego, Iñskiego, Drawskiego
i S³upeckiego w latach 2000-2002. Kleszcze zbierano od maja do paŸdziernika,
jeden raz w miesi¹cu, miêdzy 10 a 16 godz., z wyznaczonych, sta³ych stanowisk.
Stanowiska wyznaczono w pobli¿u jezior lub cieków wodnych. Aktywnoœæ
sezonow¹ kleszczy okreœlano obliczaj¹c liczebnoœæ larw, nimf oraz dojrza³ych
osobników w czasie jednego od³owu. W ci¹gu trzech sezonów wegetacyjnych
od³owiono 19649 kleszczy, w tym larw 13,1%, nimf 62,3% i postaci dojrza³ych
24,6%. Rozk³ad liczebnoœci kleszczy w poszczególnych regionach by³ bardzo
ró¿ny. Najwiêcej kleszczy zebrano w Drawskim Parku Krajobrazowym tj. 6425
osobników, przy czym zbiór ten odznacza³ siê znaczn¹ przewag¹ nimf, które
stanowi³y prawie 75% , przy prawie idealnej równowadze larw i postaci dojrza³ych
(ok. 12%). Najmniejszy z kolei zbiór (3823 osobników) mia³ miejsce w S³upeckim
Parku Krajobrazowym. Nimfy stanowi³y mniej ni¿ po³owê zbioru (ok. 47%), postacie
dojrza³e prawie 1/3 zebranej populacji, a larwy ok. 20%). Znaczna liczebnoœæ
cechowa³a zbiór kleszczy z Iñskiego Parku Krajobrazowego - 5230 osobników z
tego najwiêcej nimf - ok. 60% larw 10% i postaci dojrza³ych prawie 30%. Nieco
mniejszy zbiór dotyczy³ Szczeciñskiego Parku Krajobrazowego: 4168 kleszczy w
tym najwiêcej nimf, ok. 60%, najmniej larw, ok. 6% i postaci dojrza³ych ok. 30%
zbioru (Tab. 1). Sezonowa aktywnoœæ kleszczy w poszczególnych regionach i na
ró¿nych stanowiskach ka¿dego roku mia³a przebieg odmienny. Zwykle jednak
charakteryzowa³a siê dwoma szczytami w sezonie: wiosennym i póŸno-letnim
(Ryc. 1, Tab. 3-5). Przeciêtne zagêszczenie kleszczy dla ca³oœci zebranego materia³u
by³o wysokie i wynosi³o ok. 18 osobników/100 m 2. Natomiast na poszczególnych
stanowiskach zagêszczenie kleszczy jest bardzo ró¿ne: od 10-35 osobników/100
m 2. Krêtkami B. burgdorferi by³o zaka¿onych 4337 osobników tj. 22,1 % ca³ej
populacji, w tym zainfekowanych larw by³o 496 (19,3 %), nimf 2673 (21,8 %) i
postaci dojrza³ych 1168 (24,1 %).
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Received 30.11.2003.