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Applied and Environmental Microbiology, November 2002, p. 5595-5599, Vol. 68, No. 11
0099-2240/02/$04.00+0 DOI: 10.1128/AEM.68.11.5595-5599.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Salmonellae in Avian Wildlife in Norway from 1969 to 2000
Thorbjørn Refsum,1* Kjell Handeland,1 Dorte Lau Baggesen,2 Gudmund Holstad,1 and Georg Kapperud3,4
National Veterinary Institute,1
Department of Pharmacology, Microbiology and Food Hygiene, The Norwegian School of Veterinary Science, N-0033 Oslo,4
Division of Infectious Disease Control, Norwegian Institute of Public Health, N-0403 Oslo, Norway,3
Danish Veterinary Institute, Copenhagen, Denmark2
Received 22 February 2002/
Accepted 14 August 2002

ABSTRACT
Postmortem records of wild-living birds in Norway with laboratory-confirmed
findings of salmonella infection were summarized for the period
from 1969 to 2000.
Salmonella spp. were isolated from 470 birds
belonging to 26 species. The salmonella-positive birds included
441 small passerines, 15 gulls, 5 waterfowl, 4 birds of prey,
3 doves, and 2 crows. The bullfinch (
Pyrrhula pyrrhula) was
by far the most frequently recorded species (54% of the cases).
Salmonella enterica serover Typhimurium was recovered from all
cases except from one hooded crow (
Corvus corone), which yielded
serovar Paratyphi-B var. Java. Variant O:4,12 comprised 96%
(451 cases) of all serovar Typhimurium isolates, including all
the passerines, while variant O:4,5,12 accounted for the remaining
4% (18 cases). The occurrence of salmonellae in small passerines
showed a distinct seasonality, with a peak in February and March.
Plasmid profile analysis of 346 isolates of serovar Typhimurium
O:4,12 detected six profiles, of which two comprised 66 and
28% of the isolates, respectively. Phage typing of 52 randomly
selected isolates of serovar Typhimurium O:4,12 from passerines
detected four types: DT 40 (54%), U277 (35%), DT 99 (6%), and
DT 110 (4%).

INTRODUCTION
Bacteria belonging to the genus
Salmonella are important causal
agents of human enteritis throughout the world (
13,
39-
41).
The major source of infection is meat products from domestic
animals (
45). In Norway, the number of recorded human cases
has increased substantially in recent decades, in parallel with
the trends noted elsewhere in the industrialized world (
21,
23). However, in contrast to most other countries, the majority
(>80%) of Norwegian patients acquired their infection abroad
(
23). The favorable domestic situation in Norway is obviously
a consequence of the fact that Norwegian food-producing animals
are virtually free from salmonella (
21,
30a). However, analysis
of data on human
Salmonella enterica serovar Typhimurium infections
during 1996 to 2001 shows that about 40% of Norwegian patients
acquired the infection in Norway (
30).
It has been suggested that serovar Typhimurium has established a reservoir in avian wildlife in Norway, and epidemiological and bacteriological evidence indicate that wild birds may transmit the infection to humans (20, 22). Recently, hedgehogs have also been recognized as a source of human serovar Typhimurium infection in Norway (14, 38, 42).
Surveys conducted in Norway have shown that gulls and crows may act as healthy carriers of a broad range of Salmonella serovars (1, 4, 6, 18, 31, 37, 43; T. Refsum, G. Holstad, and G. Kapperud, submitted for publication). Moreover, serovar Typhimurium is a well-known cause of fatal salmonellosis in small passerines (such as finches and sparrows) during winter (7). The purpose of the present study was to summarize historical records of Salmonella detections in wild birds in Norway and to compare the isolates by means of plasmid profile analysis and phage typing.

MATERIALS AND METHODS
All postmortem records covering wild birds at the National Veterinary
Institute from 1969 to 2000 were examined, and all cases in
which bacteriological examination had been performed and
Salmonella bacteria had been isolated from one or more organs were included
in this study. Most of the
Salmonella-positive birds had been
examined at the Section of Wildlife Disease at the main laboratory
in Oslo (391 birds), whereas smaller numbers had been examined
at the regional laboratories in western (10 birds), central
(47 birds), and northern (22 birds) Norway. All included birds
had been submitted spontaneously by members of the general public,
except for 123 small passerines examined in a project carried
out during 1998 to 2000. Prior to the receipt of these latter
birds, the public had been encouraged to collect birds found
dead at private feeding places. The project was carried out
to study epidemiological and pathological aspects of fatal salmonellosis
in small passerines feeding places during winter. Detailed
results from this project will be published elsewhere (T. Refsum,
T. Vikøren, K. Handeland, G. Kapperud, and G. Holstad,
submitted for publication).
The methods used for isolation of Salmonella bacteria from dead birds included selective enrichment and plating on selective and differential agar media. From 1994, the presence of Salmonella was ascertained using the method recommended by the Nordic Committee on Food Analysis (29). The isolates were typed by the method of Popoff and Le Minor (33). For the great majority of the isolates, typing was conducted at the laboratory in Oslo and the results were confirmed by the National Salmonella Reference Laboratory at the Norwegian Institute of Public Health.
All available strains of serovar Typhimurium O:4,12 isolated since 1969 (n = 346; 342 isolates from small passerines and 4 isolates from other species) were characterized by plasmid profile analysis, using a small-scale modification of the alkaline lysis technique of Birnboim and Doly (5) as described by Maniatis et al. (27). Plasmid DNAs from Escherichia coli strains VA 517 (26) and J5 (R1) (17) were included as molecular weight standards.
In addition, phage typing of 52 randomly selected strains of serovar Typhimurium O:4,12 isolated from passerines from 1969 to 2000 was carried out. The typing scheme of Callow (8), as extended by Anderson et al. (3), was used.

RESULTS
Salmonella was isolated from 470 bird carcasses representing
26 different species (Table
1). The total number of birds from
which salmonellae were isolated according to year is given in
Fig.
1. The great majority of cases (
n = 441) occurred in small
passerines found dead at private feeding places, representing
14 species and comprising 94% of the total material. The remaining
cases (
n = 29) occurred in 12 species of gulls, waterfowl, birds
of prey, doves, and crows. The bullfinch (
Pyrrhula pyrrhula)
was by far the most frequently recorded species (54%), followed
by the greenfinch (
Carduelis chloris) (13%), the Eurasian siskin
(
Carduelis spinus) (11%), the common redpoll (
Carduelis flammea)
(7%), and the black-headed gull (
Larus ridibundus) (3%). The
remaining 21 species were represented by no more than 10 individuals.
Information on the number of birds submitted for examination
was available only for passerines received at the laboratory
in Oslo (Table
1). The highest percentage of salmonellae in
birds was noted among bullfinches (81%), followed by the Eurasian
greenfinch (80%), the common redpoll (78%), and the Eurasian
siskin (75%).
All isolates belonged to serovar Typhimurium, except for one isolate of serovar Paratyphi B var. Java from the hooded crow (Corvus corone) (Table 1). In small passerines, only serovar Typhimurium O:4,12 (also designated variant Copenhagen) was found, while both variants O:4,12 and O:4,5,12 were common in the nonpasserine species.
The seasonality of the cases is presented in Fig. 2. Salmonella isolations in small passerines were mainly recorded from January to April, with a distinct peak in February and March (Fig. 2). In other species, salmonellae were recorded in eight different months, without any apparent seasonality.
The first recorded cases of
Salmonella infection were detected
in epizootics among passerines in southeastern Norway in 1969.
Sporadic cases and epizootics occurred each winter in this region
until the beginning of the 1980s, when carcasses were also submitted
from western and central Norway. Since the 1980s, carcasses
have been forwarded from all 19 counties in Norway.
Plasmid profile analysis of 346 isolates of serovar Typhimurium O:4,12 detected six profile types (Fig. 3). Profile 1 was the most common, found in 228 of the cases (66%; 227 small passerines and 1 sparrow hawk, Accipiter nisus). The second most common profile was the plasmid-lacking profile 2, found in 97 of the cases (28%; 96 small passerines and 1 Tengmalm's owl, Aegolius funereus), whereas profiles 3, 4, 5, and 6 were present in 12 (3.5%; 12 small passerines), 4 (1.2%; small passerines), 4 (1.2%; 2 small passerines, 1 black-headed gull, Larus ridibundus, and 1 Canada goose, Branta canadensis), and 1 (0.3%, 1 bullfinch) of the isolates, respectively.
Phage typing of 52 randomly selected passerine isolates of serovar
Typhimurium O:4,12 detected four phage lysis patterns. The most
common phage types were DT 40 and U 277, found in 54% (
n = 28)
and 35% (
n = 18) of the isolates, respectively. The other phage
types found were DT 99 (6%,
n = 3) and DT 110 (4%,
n = 2), whereas
one isolate was termed RDNC (routine dilution, no conformity).
The relationship between phage types and plasmid profiles is
shown in Table
2.

DISCUSSION
Our findings strongly indicated that serovar Typhimurium is
endemically present in the avian fauna in Norway. In the present
study, all but 1 of a total of 470 avian
Salmonella isolates
belonged to serovar Typhimurium variant O:4,12 or O:4,5,12.
This is in accordance with a Swedish study in which these variants
accounted for 98.5% of avian salmonellae (
7). Small passerines
were invariably associated with serovar Typhimurium O:4,12,
a finding supported by studies from Sweden (
7) and Germany (
11,
24,
36). The isolates from other bird species included both
variants O:4,12 and O:4,5,12.
This study has shown that the bacterium has caused fatal disease among small passerines during most winters in Norway since 1969 (Fig. 1). A similar seasonality, as visualized in Fig. 2, has also been reported from Sweden (7, 16), Great Britain (9, 32), Germany (11), and North America (10, 12, 44). Finches (Fringillidae) like the bullfinch, Eurasian greenfinch, Eurasian sisikin, and common redpoll, were most often affected; the same species predominated in the Swedish investigation (7).
Six plasmid profiles and four phage types were detected among the small-passerine isolates in the present study. However, plasmid profiles 1 and 2 and phage types DT 40 and U277 constituted more than 90% of the isolates examined. The few plasmid profiles and phage types obtained in our study may indicate that only a few strains are circulating in the passerine fauna.
The most common phage type found in small passerines was DT 40. This is in accordance with reports from Sweden (7, 28, 35). This phage type has also been detected in passerines in Great Britain (25) and North America (44). Phage type DT 40 was previously denoted DT 1 and DT 9 in Sweden and U165 in Great Britain and North America. Our findings support the assumption that DT 40 is the most important phage type in passerines and has an extensive geographical distribution (10, 32). Phage type U277, which was the second most common, is also common in Sweden (A. Gunnarsson, personal communication). The distribution of this phage type outside the Scandinavian peninsula is unknown.
Previous bacteriological and epidemiological investigations indicate that passerines are an important source of serovar Typhimurium O:4,12 in human salmonellosis in Norway. Sporadic cases of domestically acquired human infections caused by the plasmid profile 1 variant and cases of fatal salmonellosis among passerines were most often reported at the same time of year, thus indicating an epidemiological link (22). Moreover, a case-control study identified contact with ill or dead birds or their droppings as risk factors (22). An extensive human outbreak due to contaminated chocolate bars was reported in Norway in 1987 (20). Isolates of serovar Typhimurium O:4,12 from human patients, chocolate, and wild-living passerines belonged to the same plasmid profile (profile 1) and phage type (U277) (19). In the present study, profile 1 was the most common plasmid profile and U277 was the second most common phage type detected from passerines. In addition, recent molecular epidemiological studies have shown that 32% of the isolates recovered from human patients in Norway belonged to clones detected in the small-passerine fauna (15, 34).
Serovar Typhimurium O:4,5,12 was the most common variant found in bird species other than small passerines, mainly gulls, in the present study. In recent years, this variant has been responsible for three extensive outbreaks of human salmonellosis in Norway. The sources of infection in the outbreaks in eastern Norway in 1996 and in western Norway in 2000 were traced to heavily infected hedgehog populations (14). The Norwegian hedgehog was suggested to be a reservoir host for serovar Typhimurium O:4,5,12. Further, in a waterborne variant O:4,5,12 outbreak in northwestern Norway in 1999, gulls were suggested as the most likely source of infection (2; Refsum, Holstad, and Kapperud, submitted). However, it has been speculated whether the gulls might have become infected from Salmonella-infected hedgehogs (14). This is supported by recent molecular epidemiological analyses of hedgehog and avian isolates (14, 34). The molecular epidemiological studies also indicate that different clones of serovar Typhimurium predominate among passerines, gulls, and pigeons.

ACKNOWLEDGMENTS
We thank Astrid Stovner for invaluable guidance in retrieving
historical files and Kerstin Nordby and Traute Vardund for performing
the plasmid profile analysis. We are also grateful for the data
contributed by the regional laboratories of the National Veterinary
Institute, which helped make the overview as complete as possible.
Financial support was provided by Sørlie's Foundation.

FOOTNOTES
* Corresponding author. Mailing address: Section of Bacteriology, National Veterinary Institute, P.O. Box 8156 Dep, N-0033 Oslo, Norway. Phone: 47 23 21 63 22. Fax: 47 23 21 63 01. E-mail:
thorbjorn.refsum{at}vetinst.no.


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Applied and Environmental Microbiology, November 2002, p. 5595-5599, Vol. 68, No. 11
0099-2240/02/$04.00+0 DOI: 10.1128/AEM.68.11.5595-5599.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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