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The presence of pathogenic bacteria and parasites in drinking water is a well-known cause of human disease outbreaks [14,16]. There is however, a lack of knowledge of the contamination routes to water. In Norway, the supply of drinking water to the public and the food industry is primarily based on chlorinated surface water. Since the Eurasian beaver (Castor fiber) has a widespread distribution in southern Norway [18], and lives in water, it may excrete pathogens into drinking water sources. The present study was carried out to examine whether beaver in Norway might be a reservoir of parasites belonging to the protozoan genera Giardia and Cryprosporidium, or bacteria of the genera Campylobacter and Salmonella.  Flagellates of the genus Giardia are common intestinal parasites of many mammals and are considered the most common cause of waterborne gastroenteritis in North America [7]. Giardia cysts are frequently found in Norwegian surface water sources [12] and the number of reported human cases of giardiasis is rising here [2]. In the USA, the prevalence of Giardia infection in beaver (C. canadensis) has been reported to be 7–16% [8] and the beaver is considered a potential health threat if inhabiting watersheds used as sources of drinking water [7]. The parasite is resistant to chlorination [17].  Cryptosporidium spp. are coccidian parasites causing intestinal infections in a wide range of mammals including man [19,24,29]. Cryprosporidium oocysts are frequently isolated from surface water sources in Norway [12] but the number of reported human cases of Cryptosporidiosis is low here [2]. The parasite is highly resistant to chlorination [9]. Cryptosporidium infection in beaver has been reported from Poland [4] and the USA [15].  Campylobacter spp. is the most common water and food-borne pathogen causing human enteritis in Norway [2]. The bacterium has been demonstrated in the intestinal contents of a wide variety of domestic and wild animal species [25] and is regularly isolated from river water in Telemark [26]. In Norway, human waterborne outbreaks have been traced to faecal contamination from gulls (Larus spp.), geese (Anser brachyrhynchus) and sheep [1,6,30]. [21] reported the absence of Campylobacter infection in 75 beavers examined in North America.  Salmonella contamination and salmonellosis in humans and farm animals is an increasing problem in the industrialized countries [22]. In Norway however, Salmonella is a limited problem and most of the human clinical cases (80–90%) are infected abroad [5,11]. In spite of this, a waterborne outbreak of human S. typhimurium infection has been reported here [10]. Salmonella may infect a wide range of wild and domestic mammals and birds which may also act as carriers. Salmonella spp. have also been isolated from beavers in Germany and Russia [23].  Faecal samples were collected from beavers of different sex and age-classes living in the water systems of Bo, Sauherad and Nome municipalities (59° 17'–25'N, 09° 03'–17'E) in Telemark County, southeast Norway during the years 1997–1999 (Table ​(Table1).1). The animals were either live-trapped with landing nets [27], Hancock or Bailey live-traps, or shot during the hunting season (Table ​(Table1).1). The beavers were sexed by the colour of the anal gland secretion [28] or the presence of the os-penis [20] and partitioned into three age-classes based on body weight [13]: juveniles (≤ 12 months, 24 months, ≥ 15 kg).    Table 1  The number of Eurasian beavers (Castor fiber) from Telemark County, Norway, analysed for the presence of the bacterias Campylobacter spp. and Salmonella spp., and the protozoens Giardia ...    Campylobacter was isolated from faecal swab samples brought to the laboratory and streaked out onto a selective blood free agar [CCDA-modified Preston agar, Oxoid CM 739 and SR155 supplement] within 2 hours. The agar plates were incubated at 42°C in a micro aerobic athmosphere achieved by using the Oxoid, Campy Gen code CN025A and read after 24 and 48 hours.  Salmonella was isolated by examining one gram of fresh or frozen faeces following the procedure described in NMKL 71 [3]. Giardia and Cryptosporidium detection. The ProSpectT® microplate assay for in-vitro diagnosis of Giardia and/or Cryptosporidium, Alexon inc., Sunnyvale, CA 94089, USA was used. Preliminary positive samples were followed up by individual assays. For confirmation of Giardia the ProSpectT® Giardia EZ microplate assay for in-vitro diagnosis of Giardia, Alexon-Trend, Inc Ramsey, MN 55303, USA was used. For confirmation of Cryptosporidium the ProSpecT® Cryptosporidium microplate assay, Alexon-Trend, Inc. Ramsey, MN 55303, USA was used.  Neither Giardia, Cryptosporidium, Campylobacter nor Salmonella were detected in any of the samples examined. We conclude that the beaver does not seem to be involved in drinking water contamination with these pathogens in Telemark County.

Investigations of waterborne pathogens in Eurasian beaver (Castor fiber) from Telemark County, southeast Norway.