The impact of globalisation on the distribution of Echinococcus multilocularis

Review

The impact of globalisation on the distribution of Echinococcus multilocularis Rebecca K. Davidson1, Thomas Romig2, Emily Jenkins3, Morten Tryland4 and Lucy J. Robertson5 1

Norwegian Veterinary Institute, Pb750 Sentrum, N-0106 Oslo, Norway University of Hohenheim, Parasitology Unit, Emil-Wolff-Str. 34, 70599 Stuttgart, Germany 3 University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan, S7N 5B4, Canada 4 Section for Arctic Veterinary Medicine, Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, Stakkevollveien 23, 9010 Tromsø, Norway 5 Parasitology Laboratory, Section for Microbiology, Immunology, and Parasitology, Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, PO Box 8146 Dep, 0033 Oslo, Norway 2

In the past three decades, Echinococcus multilocularis, the cause of human alveolar echinococcosis, has been reported in several new countries both in definitive hosts (canids) as well as in people. Unless treated, infection with this cestode in people is fatal. In previously endemic countries throughout the Northern Hemisphere, geographic ranges and human and animal prevalence levels seem to be increasing. Anthropogenic influences, including increased globalisation of animals and animal products, and altered human/animal interfaces are thought to play a vital role in the global emergence of this pathogenic cestode. Molecular epidemiological techniques are a useful tool for detecting and tracing introductions, and differentiating these from range expansions. Echinococcus multilocularis: an unwanted stowaway Increased travel, growth in international trade and animal introductions are all consequences of the past few centuries of intensified globalisation. Human exploration, expansions and new settlements not only lead to the introduction of alien species to new environments but also their pathogen fauna. Introduction of definitive hosts, canids, and intermediate hosts, rodents, have enabled the zoonotic parasite E. multilocularis (Figure 1) to spread. The recently recorded presence of infected foxes in Sweden and the discovery of a European genotype in North America are thought to have been caused by accidental translocation with dogs [1,2], while introductions with wildlife, accidental or intentional, have occurred in Great Britain, Svalbard Archipelago (Norway) and Japan [3–5]. Globalisation has had, and continues to have, an impact on the distribution of E. multilocularis. It is timely to summarise current knowledge on the prevalence, distribution and genetics of this parasite given the recent findings in Sweden and the United Kingdom (UK), rapid changes in landscape and climate [6], as well as changes in European Union (EU) legislation regarding pet travel and tapeworm Corresponding author: Davidson, R.K. ([email protected]) Keywords: Echinococcus multilocularis; human alveolar echinococcosis; AE.

treatment. Thus, the aim of this article is to consider evidence for anthropogenic influences on the emergence of E. multilocularis across the Northern Hemisphere and provide an update, since the last WHO/OIE report in 2001 [7], on the geographic distribution of E. multilocularis in definitive hosts and people (Box 1, Figure 2a). New information about genotypes of E. multilocularis is linked to geographic location. Recent findings that E. multilocularis is not genetically uniform across its distribution in the Northern Hemisphere [8,9] may also have significance for understanding pathogenicity, host specificity and zoonotic potential. Prevalence and distribution in Europe: a parasite on the move? Since the 1980s the autochthonous presence of E. multilocularis has been reported in 17 European countries that were previously considered non-endemic [10,11] (Table 1, Figure 2b). It remains unclear whether the earlier lack of records in these ‘new’ regions reflects a true absence. Even well-designed surveys with negative results only provide probabilities, not proof, of absence. E. multilocularis distribution is not homogeneous and even in low or nonendemic regions, small ‘islands’ of infection may be present [12]. The restricted distribution of E. multilocularis in Northern Italy, apparently limited to the Trentino Alto Adige region and originally speculated to represent overspill from neighbouring regions of Western Austria, may be one such example [13]. Such foci may have been overlooked in other regions and may have been the source for the surge in transmission seen subsequent to the rapid increase in red fox densities during the 1990s. Current evidence, based on studies in different periods, supports a northward expansion during the late 1990s within Belgium and the Netherlands [14,15], and a southeastern expansion in Hungary and Central Germany [16,17]. The northward expansion of the parasite in Europe also raises questions about effects of climate change on the distribution of E. multilocularis, as has been reported in other regions [6,18,19].

1471-4922/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.pt.2012.03.004 Trends in Parasitology, June 2012, Vol. 28, No. 6

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Echinococcus multilocularis lifecycle Adults develop in the small intestine, are 2–4 mm long and have 3–5 segments

IMH eaten by definitive host

Definitive host Canids (+/– cat)

Eggs are passed in the faeces Eggs are 30–40 μm in diameter, patency lasts between 2 and 4 months depending on definitive host species

Alveolar hydatid cysts develop in the IMH

Intermediate host (IMH)

Eggs ingested by suitable IMH, such as rodents, or aberrant hosts such as humans

Environment Eggs contaminate the environment E. multilocularis eggs - Extremely freezetolerant - Heat-sensitive

- Long survival times in cool damp conditions Human alveolar echinococcosis It can take 10–15 years between infection point and the development of clinical symptoms

- Cannot be differentiated morphologically from other taeniid eggs TRENDS in Parasitology

Figure 1. The lifecycle of Echinococcus multilocularis. Photos courtesy of I.S. Hamnes (red fox), Ø. Øines (E. multilocularis adult and egg) and R.A. Ims (sibling vole).

Improved awareness and better diagnostic tools, particularly molecular methods, have probably also contributed to the increasing records of this parasite. That alone is not a sufficient explanation for the apparent surge in parasite abundance, coinciding with fox population increases subsequent to the elimination of fox rabies [20]. The lack of prior records in animals and previous absence of human alveolar echinococcosis (AE) (Box 2) in new endemic regions, such as parts of Belgium, Central Germany, the High Tatra region (Slovakia/Poland) and the Baltic states, would seem to indicate that parasite abundance has increased dramatically [21]. There are few long-term studies that allow identification of temporal trends of E. multilocularis prevalence estimates in animals. In Southwest Germany, the prevalence in foxes seems to have more than doubled between the 1970s and 1990s [22], and parasite abundance is estimated to have increased tenfold between 1990 and 2000 [21,22]. In Northwestern Germany, the prevalence estimates of E. multilocularis in the red fox have increased from approximately 12% to 20% between 1991 and 2005 [23], and in Central Germany from 12% to 42% between 1990 and 2009 [17]. In several other areas of Europe, a similar trend in foxes has been recorded [14,24,25]. The emergence of ‘urban’ foxes in towns and cities in Central Europe has established this parasite in completely novel environments, such as parks and other recreational areas [26]. This brings the parasite into closer contact with human populations, increasing the need for control strategies. An invasive new host species, the raccoon dog (Nyctereutes procyonoides), may also play a 240

role in the transmission cycle, by providing an additional reservoir of definitive hosts [27]. Although infection studies indicate that raccoon dogs are suitable hosts for E. multilocularis [28], recently published surveys suggest that foxes continue to play the predominant role as definitive hosts in regions where both species are found [29]. The generally small number of human AE cases and inconsistent methods of case registration mean that recognition of temporal trends is challenging. In addition, improved diagnostics, such as specific serological tests in combination with imaging techniques, have increased diagnostic possibilities in humans [30]. Nevertheless, in Latvia and Lithuania, patient numbers seem to have been rising since 2002 [31,32], and the mean annual incidence of human cases per 100 000 population, recorded with consistent methods, has more than doubled in Switzerland, from 0.10 between 1993 and 2000, to 0.26 between 2001 and 2005 [30]. This follows a dramatic increase in the fox population size that began 10–15 years earlier [33]. Prevalence trends of AE in humans appear to follow parasite abundance in wildlife [33]. Individual infection risk, however, seems to be more closely linked to behavioural patterns (hygiene, contact with definitive host animals) rather than parasite abundance in the environment. The most recent case–control study [34], as well as historical reports from highly-endemic foci in Alaska [35], suggests that owning pet dogs – with access to the outdoors – may be the highest risk factor. Concern related to food consumption, such as eating berries or other raw produce from the environment, has not been substantiated [34–36].

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Box 1. A brief summary of Echinococcus multilocularis distribution North America In North America, the proposed distribution of E. multilocularis is divided into the Northern Tundra Zone (NTZ) and the North Central Region (NCR) (Figure 1a) [7,70]. The prevalence on St. Lawrence Island (SLI) and Nunivak Island, in the Alaskan portion of the NTZ has been as high as 70–80% in Arctic foxes (Vulpes lagopus). Elsewhere in the NTZ, E. multilocularis prevalence is low (2–8%) [69,71–73]. The prevalence in red foxes (Vulpes vulpes) in the US part of the NCR, ranges from 5% to 89% and appears to be expanding south and east [70]. Coyotes (Canis latrans) play an important role in the ecology of E. multilocularis in the NCR, in which prevalence ranges from 19% to 35% [70]. Only two autochthonous cases of human alveolar echinococcosis (AE) in North America have been reported to date [40]. Western and Central Europe The range of E. multilocularis in Europe expanded from four countries in the core region in the 1980s to include an additional eight countries by 2001 [7]. During the past decade, E. multilocularis has been reported in red foxes in a further nine European countries [7], at prevalence ranging from 0.1% to 57% (Table 1, Figure 1b) [1,11,31,55,74–78]. New reports in red foxes in Central and Eastern Europe may be a result of increased surveillance efforts as well as ongoing range expansion. The new reports from Northern Europe may reflect range expansion alone; given the long-term surveillance programmes in place in some countries [79] and that human AE has yet to be reported in the northernmost of the nine newly endemic countries (Denmark, Estonia and Sweden) [11]. The number of human cases has more than doubled during the past two decades in Switzerland and possibly other

In Japan, drinking well water, rather than tap water, was an epidemiological risk factor [37]. Echinococcus multilocularis distribution: the molecular map A globally accessible and accepted genetic fingerprinting system is necessary to detect introductions and trace the origins of global translocations of E. multilocularis. Information obtained from three systems that have been used to date is provided in Table 1. North America Some of the highest historical incidences of human AE are recorded from St. Lawrence Island (SLI) and Western Alaska. This may be linked to the presence of Asian strains of E. multilocularis, as well as cultural and ecological risk factors [8,38]. Two Asian mitochondrial haplotypes (Figure 1a), and one North American (N1) haplotype, as well as a unique EmsB microsatellite profile, have been described from rodents from SLI [8,39]. On the Arctic mainland, E. multilocularis closely related to Asian genotypes (based on the nad1 mitochondrial gene) was recently described in 27% of 26 Arctic foxes from Barrow, Alaska (C. Kirk, PhD thesis, University of Alaska Fairbanks, 2011), whereas E. multilocularis with an EmsB microsatellite profile similar to that from SLI was detected in two Arctic foxes, of 256 examined from Western Nunavut, Canada (K. Gesy et al., unpublished). A second North American haplotype (N2) has been found in Indiana and South Dakota, USA [8], and also in Southern Saskatchewan, Canada (K. Gesy et al., unpublished). Despite regular detection of cystic hydatid disease caused by Echinococcus granulosus, only two autochthonous cases

countries from the core endemic region (Austria, France and Germany) [30]. Asia and Eastern Europe Russia and adjacent countries (Belarus, Ukraine, Moldova, Turkey, Armenia, Azerbaijan, Kazakhstan, Turkmenistan, Uzbekistan, Tajikistan, Kyrgyzstan and Mongolia), nine provinces/autonomous regions in China (Tibet, Sichuan, Inner Mongolia, Gansu, Ningxia, Qinghai, Xinjiang, Heilongjiang and Shaanxi) and the Japanese island of Hokkaido remain important endemic foci of E. multilocularis [50,52,80–84]. In Russia and adjacent countries, little recent data are available: 7% (n = 94) of red foxes in Belarus were positive, and human AE cases have been reported from Turkey and Kazakhstan [83,85]. In Central Asia the distribution seems to be linked to patchy areas around wetlands and at higher altitudes [86]. In some provinces in China prevalence of up to 60% in foxes and 5–15% in dogs are reported [80]. Human AE is highly endemic in three main foci in China with by far the largest number of human cases in the world, with prevalence ranging from 0.2% in Northwestern Xinjiang to 4% in Gansu and Northwestern Sichuan [80]. Individual villages had even higher recorded prevalence, including the highest ever human prevalence found worldwide: 16% in the village of Ban Ban Wan, Gansu [87]. Little is known on temporal changes of the parasite’s range and transmission patterns in continental Asia, apart from some effect of deforestation and rodent control measures in parts of China [52]. In Hokkaido, Japan, E. multilocularis increased in both range and prevalence in definitive hosts in the 1980s and 1990s [5], from 19% between 1966 and 2003, to around 40% by 2006 [88]. It remains controversial as to whether the parasite has colonised Honshu and whether human AE cases from Honshu are autochthonous [5,81].

of human AE have ever been confirmed in Central Canada and the US; the latter was determined to be the N2 strain [40]. In Central North America, human infection with E. multilocularis does not seem to be common, even in highly exposed populations, such as fox and coyote trappers in an endemic region [41]. This is despite a high prevalence and intensity of infection in wild canids; 23 of 91 coyotes in a recent study in urban regions of Western Canada had adult E. multilocularis, at intensities of up to 1400 adult cestodes per host (Catalano, S. et al., unpublished). In 2008, the EU reported an annual incidence of 1 case/10 million inhabitants [42], whereas between 1990 and 2007, the US reported an annual incidence of 1 case/2.5–3 billion inhabitants [43]. This difference in incidence seems unlikely to be solely due to decreased risk of exposure of North American inhabitants. It is possible that genetic differences among strains of this parasite partly account for the low prevalence of AE in Central North America, rather than simply differences in epidemiological risk factors between North Americans and other populations in the Northern Hemisphere. Europe Maximal genetic diversity is reported from the core endemic region: Austria, France, Germany and Switzerland, as could be expected with a pathogen undergoing range expansion. However, most isolates for molecular characterisation have originated from these regions, especially France and Switzerland (Table 1). Molecular data on microsatellite patterns and mitochondrial sequences support a ‘mainland-island’ hypothesis, with a mainland of greater genetic diversity in Northern Switzerland and Southwestern Germany, and lower diversity, including founder 241

Review (a)

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N1 A2 A4 E1–5 NTZ ∗E

NCR

A1&2

N2

O1

A3&4

A5–10

Key: Highly endemic Endemic L#

Genotype

3

(b) 2

1

?

4 5

?

? 8 6

9 7 ?

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Figure 2. Echinococcus multilocularis distribution in the Northern Hemisphere. (a) Distribution of E. multilocularis in the Northern Hemisphere, adapted from Eckert et al. [7]. The range in continental Asia and Arctic America is approximate due to patchy distribution and lack of comprehensive surveys. Genotypes are as per the mitochondrial haplotyping system proposed by Nakao et al. [8]. NTZ refers to the Northern Tundra Zone (Alaska and Canada), and NCR refers to the southern half of the three Canadian prairie provinces and 13 contiguous North-central US states. Transparent grey area over Europe demonstrates new reports since 2001 and is shown in more detail in (b). *E refers to the location of a European-type isolate detected for the first time in Canada. (b) New reports of E. multilocularis in red foxes (Vulpes vulpes) in Europe between 2001 and 2011. Light grey indicates the approximate current area of distribution, whereas darker grey indicates the estimated highly endemic regions. Question marks indicate that presence is likely but unconfirmed. Country codes: 1, Denmark; 2, Sweden; 3, Estonia; 4, Latvia; 5, Lithuania; 6, Italy; 7, Slovenia; 8, Hungary; 9, Romania.

effects, in peripheral areas [9,44]. South-central Europe may, therefore, constitute a core region from where expansion(s) occurred in the past. Nonetheless, the very rapid changes over the past two decades are suggestive of expansions from several previously unrecognised ‘islands’ at the periphery of the endemic area. This relatively recent range expansion is supported by the wide European distribution of the same microsatellite NAK1 genotypes (195 and 198) 242

and EmsB profiles D and H [39,45]. EmsB profiles have been used to demonstrate that E. multilocularis in Northern Italy was not a range expansion from Austria, but instead had most likely been circulating undetected in foxes for some time [13]. Interestingly, documents from the 19th century record the diagnosis of AE in five persons living in the same area, further suggesting that the parasite had been established there for a considerable period [13].

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Table 1. Echinococcus multilocularis distribution, prevalence and genotype in Europea European country

Prevalence in foxes in 2001 [7]

Austria Belgium Bulgaria Czech Republic Denmark b Estonia b France

7.8% (294/3778) 35.4% (92/260) Rodents only 14.0% (214/1528)

Germany Greece Hungary b Italy b Latvia b Liechtenstein Lithuania b

15.4% (6556/42545)

Netherlands Norway (Svalbard) Poland Romania b Slovak Republic Slovenia b Sweden b Switzerland

Prevalence in foxes: reports from the past decade

0.9% (3/340) [55] 29.4% (5/17) [77] 24.6% (136/552)

NA 5.0% (5/100) [75] 0.6% (2/360) [76] 35.6% (16/45) [44] 34.9% (45/129) 57.3% (118/206) [31] 1.8% (5/272) Rodents only 2.6% (76/2951)

8.5% (30/353) [90] 23.8% (360/1514) [25] 4.8% (27/561) [11]

10.7% (6/56) 2.6% (11/428) [78] 0.1% (2/1444) [1] 29.7% (2217/7457)

AE in people

Endemic Endemic Suspect Sporadic None reported None reported Endemic Endemic Sporadic Sporadic [75] Historically present Sporadic [44] Endemic 80 cases: 1997–2006 [31] None reported None reported Endemic Two cases [11] Sporadic Sporadic None reported Endemic

Genotype

NAK1 c 195, 198, 195 + 198

EmsB d D,H

Mitochondrial e E1 E4

195, 198

D,G

198, 195, 201, 198 + 201 195, 198

D,H

E2, E3, E4

D,G,H

E2

195, 198

D,H

198, 198 + 201

D,H

198

D,H

195, 198, 201, 192, 195 + 198

E,F,G,H

E5

a

Prevalence of Echinococcus multilocularis in red foxes (definitive hosts, Vulpes vulpes) and people (AE) in Western and Central Europe as reported in 2001, by the World Health Organisation/World Organisation for Animal Health, and new country reports and genotypes (using microsatellite and mitochondrial loci) reported in the past decade.

b

European countries with first reports of E. multilocularis in foxes after publication of Eckert et al. [7].

c

NAK1 is a single locus microsatellite (a tandemly repeated sequence of nuclear DNA) for which five homozygote and two heterozygote genotypes have been described for E. multilocularis [39,45].

d

EmsB is a multilocus microsatellite target, for which eight unique profiles or electropherograms are described for E. multilocularis [45].

e

Mitochondrial haplotypes determined by sequencing at three mitochondrial loci, NADH dehydrogenase subunit 2 (nad2), cytochrome b (cob) and cytochrome c oxidase subunit 1 (cox1), and corresponding to distinct North American (n = 2), Asian (n = 10) and European (n = 5) haplotypes of E. multilocularis [8]. The O1 haplotype from Inner Mongolia described in this paper may be synonymous with the recently proposed E. russicensis [82].Abbreviation: AE, alveolar echinococcosis.

Evidence of anthropogenic influences on the spread of Echinococcus multilocularis In North America In 2009, the alveolar hydatid (metacestode) stage of E. multilocularis was detected in a dog with no previous history of travel outside British Columbia (BC), Canada, 600 km to the west of the accepted E. multilocularis range in Central North America (Figure 2a) [2,46]. This isolate was most similar to mitochondrial and microsatellite genotypes in Europe, rather than native North American genotypes [2,8,39]. These data suggest a relatively recent introduction, rather than range expansion from the north or the east of native North American strains. The source of this introduction could have been an imported domestic dog, as has been suspected in other countries [1]. Yet, it is also possible that the parasite was already established in BC but was undetected, rather than a recent point source introduction. There are highly successful populations of non-native foxes of European origin throughout the Western Canadian provinces and Pacific coastal US states, which thrive in peri-urban and agriculturally fragmented environments [47]. In the past century,

red foxes of European origin (UK, France and Scandinavia) were introduced in the Pacific coastal states and Eastern US, and have since moved north and west, respectively, across North America [47]. Foxes, of unknown provenance, may have also escaped from fur farms throughout Southern BC [48]. As BC is a coastal province, other possibilities include introduction of the parasite via translocation of intermediate hosts with international shipping. If a European-type strain has established in native Canadian wildlife and pets, this may have significance for veterinary and public health. European strains may be generally less intermediate host-specific given that canine cases of AE have only been reported from highly endemic regions in Europe [49]. The current lack of screening requirements for E. multilocularis in pets imported into North America, along with a complex history of exotic wildlife translocation, make it likely that this parasite will continue to emerge in North America. In Asia In Japan, E. multilocularis was probably introduced with foxes on at least two separate occasions. In the 1920s red 243

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Box 2. Alveolar echinococcosis in animals and man Foxes, domestic dogs and other canids are the definitive hosts for the adult stage of the parasite (Figure 1). The scolex of the tapeworm attaches to the intestinal mucosa by hooks and suckers. Hundreds of microscopic eggs are produced per parasite and excreted with the faeces. The adult stage of the parasite normally causes little harm to the definitive host and infection is asymptomatic. In intermediate hosts, such as small rodents, ingested eggs develop to oncospheres, which penetrate the intestinal wall and are carried via blood to the liver, lungs and other organs where they form multilocular cysts. These cysts, over time, occupy tissues and organs at the expense of normal function (Figure 1; sibling vole). The severity of disease depends on which organs are affected and to what extent. However, as the life of most intermediate hosts is normally very short it is uncertain how much the parasite results in reduced fitness and increased predation (reduced survival) or disease in typical intermediate hosts [54]. E. multilocularis is of significant public health concern as people may act as accidental intermediate hosts after ingesting eggs, either through contaminated foods or water, or from contact with infected definitive hosts (dogs, foxes) and/or their faeces. Parasite eggs are extremely environmentally resistant and can remain viable for months or years. The time from ingestion of eggs to onset of clinical symptoms (incubation time) in people may be from months to years,

foxes were deliberately moved, as a rodent control measure, from E. multilocularis endemic Kuriles, to Rebun Island off the northwestern coast of Hokkaido. This resulted in more than 100 human cases, mostly before 1960 [5]. The parasite was eliminated there by the mid20th century, along with the local dog and fox populations. A second, undocumented introduction probably occurred in Eastern Hokkaido before 1965, when human cases began to occur there. By the 1980s the parasite had spread throughout Hokkaido, accompanied by significant increases in E. multilocularis prevalence in foxes [5]. A total of 222 human cases were recorded between 1965 and 1997. Since then, 10–20 new cases are diagnosed annually [5]. Foxes in Hokkaido have adapted to human environments and become urbanised. The transmission of E. multilocularis is now established on the outskirts of Sapporo, the fourth-largest city of Japan [50]. Overgrazing by yak, horses and sheep in Ganzi Tibetan Autonomous Prefecture in Northwest Sichuan Province, China, has also been associated with increased transmission of E. multilocularis, probably due to the resultant explosion in small rodent and lagomorph populations that serve as intermediate hosts; specifically Ochotona spp., Microtus spp. and Cricetulus kamensis [51]. In parts of China (Southern Gansu and Ninxia provinces), the parasite has apparently benefitted from large-scale deforestation, which created new habitats for rodent hosts. In the same region, local elimination of the parasite was also observed, linked to large-scale poisoning of rodents and secondary poisoning of foxes and dogs [52]. In Europe The lifting of border restrictions in Europe has meant that pet owners can mostly travel freely with their animals. However, historically non-endemic countries (UK, Finland, Malta, Ireland and Norway) have specific regulations demanding treatment of dogs and cats for tapeworms before entry (EU Directive 998/2003). The treatment requirements were only harmonised between the different 244

and even decades, depending on the location of the cysts and how fast they grow. It is difficult to detect human alveolar echinococcosis (AE) in the early stages. In approximately 99% of human AE cases, metacestodes of E. multilocularis initially develop in the liver [54], with hydatid cysts varying from a few millimetres up to 15–20 cm or more in diameter. The cysts can also reproduce aggressively by asexual lateral budding. This gradual invasion of adjacent tissue in a tumour-like manner is the basis for the severity of this zoonosis. Metacestodes may also spread from the liver to other internal organs, such as the lungs, spleen, heart and kidney. Symptoms of severe hepatic dysfunction appear in the advanced clinical stage, in addition to symptoms from other affected organs. Diagnosis is dependent upon a combination of serology, imaging techniques (ultrasound, Xray, CT scan and magnetic resonance imaging), histopathology and/ or nucleic acid detection. Because of its proliferative and invasive characteristics, human AE is difficult to treat. Radical resection is the primary goal, and excision of the entire parasitic lesion should follow the rules of tumour surgery [54]. Untreated, human AE used to have a fatality rate of 90% within 10 years. Since the introduction of anthelmintic treatment (benzimidazoles) in 1976, the prognosis has much improved. Anthelmintic treatment is used post-surgery and also as a long-term (possibly life-long) treatment in inoperable patients.

countries from 1st January, 2012 (EU Directive 1152/ 2011). Many pet owners and veterinarians apparently find these different regulations problematic, and advice provided by veterinarians to their clients is often inadequate or, in some cases, inaccurate [53]. Given the lack of border controls and the paucity of easily accessible veterinary advice, it is not surprising that many pet owners do not comply with the treatment regulations. For example, Norwegian authorities stipulate that dogs and cats are treated twice (once before entry and once post-entry), but no controls are in place to ensure compliance [54]. Human error and oversight, as well as infrequent border checks, may lead to the inadvertent introduction of E. multilocularis into new regions. It therefore comes as no surprise that dogs, rather than wildlife, are the prime suspects for the introduction of E. multilocularis into Sweden and Denmark [1,55,56]. Illegal pet imports are also of considerable concern, especially within Europe. It is widely recognised that tens of thousands of pets are trafficked in Europe annually [57]. They are illegally transported, either without identification papers or with falsified or forged documents. Thus, these animals are likely candidates for transporting E. multilocularis, as well as other pathogens, into new areas. Wildlife relocation and reintroduction Wildlife reintroduction projects, which attempt to re-establish species within their historical ranges in regions of local extinction through release of wild or captive-bred individuals, have increased markedly in recent years [58]. A Reintroduction Specialist Group (RSG), part of the Species Survival Commission of the International Union for the Conservation of Nature and Natural Resources, provides guidelines for reintroduction programmes, including the potential introduction of pathogens. E. multilocularis is one possible candidate for introduction during such projects, particularly in intermediate host species, where early infections may not be clinically detectable and there is long latency. In 2010, a beaver,

Review originally introduced to the UK from Germany in 2007 and held within a 2-acre closure after the 6-month quarantine period, was autopsied, and extensive E. multilocularis lesions were found in the liver [3]. Adequate monitoring and biosecurity, as appropriate, is thus important for ensuring that wildlife reintroduction does not involve simultaneous introduction of E. multilocularis. International trade In addition to international movement of potentially infected animals (Box 3), E. multilocularis could also be introduced to countries via fresh produce. Outdoor grown vegetables and berries contaminated with fox or dog faeces were long suspected to be a source of infection with E. multilocularis. Nevertheless, the consumption of raw outdoor produce did not emerge as an important risk factor in a German study and other factors had considerably higher odds ratios [34]. Some studies have found no association between infection and consumption of raw produce [35,36]. A recent risk assessment from Norway concluded that import of E. multilocularis to Norway via produce is unlikely [54]. Echinococcus multilocularis: prevention of parasite spread Human AE is relatively rare in developed countries: only 23% of 358 confirmed cases of echinococcosis in Europeans in 2009 were due to E. multilocularis (AE), as compared to E. granulosus (cystic echinococcosis) [59]. However, it should be noted that less than 50% of the 790 cases of echinococcosis diagnosed in Europe during 2009 were speciated. It is difficult to define and implement preventative measures because risk factors, such as rural habitation and dog ownership, are not easy to mitigate [34]. In a recent survey, information levels and attitudes towards echinococcosis were found to vary considerably in four European countries [60]. This means that any public health information has to (i) provide a clear explanation of the disease and (ii) enable realistic public risk perception. Effective risk communication with high-risk groups, such as hunters, farmers and dog owners, should emphasise simple achievable actions: deworm dogs with access to

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the outdoors and wash hands well after contact with canines and carnivore faeces. The emerging urban E. multilocularis transmission cycle calls for targeted education campaigns on how to deal with foxes and fox faeces in this setting. All information and education activities should be coordinated by public health authorities. Control of wildlife host populations is frequently suggested as one method by which the spread of pathogens can be restricted [61,62]. However, this is unlikely to have the desired effect, given wildlife mobility in response to increased hunting pressure. Reduction of wildlife host densities (foxes or rodents) is not only regarded as inefficient but also considered unethical for disease control in many countries. Trials have been carried out in Europe and Japan to test the efficacy of deworming of foxes using anthelmintic baits. All studies, in areas varying from 90 to 5000 km2, achieved considerable reduction of E. multilocularis prevalence after repeated bait distribution [63–65]. Only in one ongoing study does local elimination appear to be within reach [65], but the cost- and labour-intensive approach chosen (air distribution combined with hand delivery of baits in rural and settled areas) limits the application to high-risk areas in affluent countries. An alternative to largescale baiting is local distribution of baits in small peri-urban areas with high fox–human contact. This approach has provided promising results regarding efficacy and long-term effects [66,67]. Management efforts in wildlife should also be complemented by those in companion animals. A marked reduction in prevalence, from 29% to 1%, was shown in rodents following a decade-long deworming program in dogs in a village in SLI [68]. Echinococcus multilocularis in the future E. multilocularis seems to be on the increase. In Europe, this parasite is becoming more prevalent and is spreading to new countries through the movements of wildlife and/or domestic animals. We have already highlighted the need to incorporate recognition of genetic diversity into regulations and risk assessments concerning global translocation of zoonotic pathogens. Genetic analysis at appropriately discriminatory loci can provide evidence of the origin of parasite spread, as well as differentiating range expansions

Box 3. Svalbard: the sibling vole story The Svalbard Islands, in the Norwegian high Arctic, have terrestrial ecosystems with very few species. The only wild terrestrial mammals present are Svalbard reindeer (Rangifer tarandus platyrhyncus), the Arctic fox (Vulpes lagopus) and the polar bear (Ursus maritimus), although the latter are characterised as marine mammals, due to their total dependency on the marine food chain. In general, there are no rodents on Svalbard. However, at some point between 1920 and 1960, the sibling vole (Microtus levis) was accidentally introduced to Spitsbergen from Eastern Europe, probably in imported animal fodder transported by sea freight. A small colony of voles has existed since then. They are localised around the former Russian mining settlement of Grumant, but the population size fluctuates annually. In some years, the vole colony can reach as far as Longyearbyen, the administrative centre of Svalbard with approximately 2000 inhabitants and close to 600 dogs, the majority sled dogs. The parasite itself was probably introduced to Svalbard by infected Arctic foxes migrating over the sea ice, a hypothesis [4] which is supported by recent genetic evidence [89]. Together, the Arctic fox and the sibling vole serve as a sustainable host system for

E. multilocularis. Almost 100% of overwintering sibling voles are infected (Figure 2) [4]. The prevalence in foxes is positively correlated to the local abundance of voles [90]. Based on a survey of fox scats, the risk of human exposure to the parasite seems to be limited to the region occupied by the sibling vole [91]. Although infected foxes may migrate considerable distances during the 3 months that the parasite survives in the fox gut, the prevalence of vole-transmitted cestodes, including E. multilocularis, was found to be highest in the Arctic foxes caught within 0–10 km of the vole population, and decreased with increasing distance from the vole population [90]. These findings reveal that there is potential risk for human E. multilocularis exposure in most regions of Svalbard. The Norwegian Food Safety Authority has recommended rodent population control during peak population years, when it extends into settlements. Regular treatment of dogs with anthelmintics is also advised. Public health education is emphasised, especially for those conducting fieldwork on voles and Arctic foxes. These biologists are at particular risk of exposure to the parasite and several seropositive workers have been reported [4]. 245

Review from point source introductions. The European regulations to prevent further spread of E. multilocularis are insufficient in light of the lack of controls in place to ensure treatment compliance and to consistently advise pet owners. It is just a matter of time until this parasite spreads further in Europe and North America, and this has been generally concluded in risk assessments from countries that are currently deemed to have freedom status [54,69]. Effective public health measures are limited to either expensive wildlife treatment programs, reliant on political will for long-term funding, or privately funded pet treatment. In affluent regions, such as North America, Europe and Japan, such treatment programs might be feasible. However, looking at figures of human cases, the situation in Western China and adjacent regions are currently of highest concern, and control strategies based on local conditions there are a matter of priority. Perhaps the biggest challenge is not in trying to restrict the spread of the parasite, which seems to be a losing battle, but in educating the general public and public health policy makers with regard to simple and consistent risk communication on risk factors and protective actions. Acknowledgements Many thanks to Dr. Rolf A. Ims (the sibling vole), Dr. Inger Hamnes (the red fox) and Dr. Øivind Øines (the E. multilocularis adult and egg) for the use of their photographs (Figure 1).

References 1 Osterman Lind, E. et al. (2011) First detection of Echinococcus multilocularis in Sweden, February to March 2011. Euro Surv. 16, pii: 19836 2 Jenkins, E.J. et al. Detection of a European strain of Echinococcus multilocularis in North America. Emerg. Infect. Dis. http://dx.doi.org/ 10.3201/eid1806.111420 (in press) 3 Barlow, A.M. et al. (2011) Echinococcus multilocularis in an imported captive European beaver (Castor fiber) in Great Britain. Vet. Rec. 169, 339 4 Henttonen, H. et al. (2001) Echinococcus multilocularis on Svalbard: introduction of an intermediate host has enabled the local life-cycle. Parasitology 123, 547–552 5 Ito, A. et al. (2003) Perspective on control options for Echinococcus multilocularis with particular reference to Japan. Parasitology 127, S159–S172 6 Miterpa´kova´, M. et al. (2006) Climate and environmental factors influencing Echinococcus multilocularis occurrence in the Slovak Republic. Ann. Agric. Environ. Med. 13, 235–242 7 Eckert, J. et al. (2001) WHO/OIE Manual on Echinococcosis in Humans and Animals: A Public Health Problem of Global Concern, WHO/OIE 8 Nakao, M. et al. (2009) Geographic pattern of genetic variation in the fox tapeworm Echinococcus multilocularis. Parasitol. Int. 58, 384–389 9 Knapp, J. et al. (2009) Genetic diversity of the cestode Echinococcus multilocularis in red foxes at a continental scale in Europe. PLoS Negl. Trop. Dis. 3, e452 10 Romig, T. et al. (2006) The present situation of echinococcosis in Europe. Parasitol. Int. 55, S187–S191 11 Siko´, S.B. et al. (2010) Echinococcus multilocularis in southeastern Europe (Romania). Parasitol. Res. 108, 1093–1097 12 Tanner, F. et al. (2006) Echinococcus multilocularis in Grisons: distribution in foxes and presence of potential intermediate hosts (in German). Schweiz. Arch. Tierheilkd. 148, 501–510 13 Casulli, A. et al. (2009) Multi-locus microsatellite analysis supports the hypothesis of an autochthonous focus of Echinococcus multilocularis in northern Italy. Int. J. Parasitol. 39, 837–842 14 Vervaeke, M. et al. (2006) Spatial spreading of Echinococcus multilocularis in red foxes (Vulpes vulpes) across nation borders in Western Europe. Prev. Vet. Med. 76, 137–150 246

Trends in Parasitology June 2012, Vol. 28, No. 6

15 Takumi, K. et al. (2008) Evidence for increasing presence of Echinococcus multilocularis in foxes in the Netherlands. Int. J. Parasitol. 38, 571–578 16 Casulli, A. et al. (2010) Spatial distribution and genetic diversity of Echinococcus multilocularis in Hungary. Vet. Parasitol. 174, 241–246 17 Staubach, C. et al. (2011) Bayesian space-time analysis of Echinococcus multilocularis-infections in foxes. Vet. Parasitol. 179, 77–83 18 Mas-Coma, S. et al. (2008) Effects of climate change on animal and zoonotic helminthiases. Rev. Sci. Tech. 27, 443–457 19 Jenkins, E.J. et al. (2011) Old problems on a new playing field: Helminth zoonoses transmitted among dogs, wildlife, and people in a changing northern climate. Vet. Parasitol. 182, 54–69 20 Gloor, S. et al. (2001) The rise of urban fox populations in Switzerland. J. Mamm. Biol. 66, 155–164 21 Romig, T. (2002) Spread of Echinococcus multilocularis in Europe? In Cestode Zoonoses: Echinococcosis and Cysticercosis (Craig, P.S. and Pawlowski, Z.S., eds), pp. 65–80, IOS Press 22 Romig, T. et al. (1999) Echinococcus multilocularis in animal hosts: new data from Western Europe. Helminthologia 36, 185–191 23 Berke, O. et al. (2011) Emergence of Echinococcus multilocularis among red foxes in northern Germany, 1991–2005. Vet. Parasitol. 155, 319–322 24 Ko¨nig, A. et al. (2005) Drastic increase in the prevalence of Echinococcus multilocularis in foxes (Vulpes vulpes) in southern Bavaria, Germany. Eur. J. Wildl. Res. 51, 277–282 25 Malczewski, A. et al. (2008) Infection of red foxes (Vulpes vulpes) with Echinococcus multilocularis during the years 2001–2004 in Poland. Parasitol. Res. 103, 501–505 26 Deplazes, P. et al. (2004) Wilderness in the city: the urbanization of Echinococcus multilocularis. Trends Parasitol. 20, 77–84 27 Sutor, A. (2008) Dispersal of the alien raccoon dog Nyctereutes procyonoides in southern Brandenburg, Germany. Eur. J. Wildl. Res. 54, 321–326 28 Kapel, C.M.O. et al. (2006) Reproductive potential of Echinococcus multilocularis in experimentally infected foxes, dogs, raccoon dogs and cats. Int. J. Parasitol. 36, 79–86 29 Bruzinskaite-Schmidhalter, R. et al. (2012) Helminths of red foxes (Vulpes vulpes) and raccoon dogs (Nyctereutes procyonoides) in Lithuania. Parasitology 139, 120–127 30 Moro, P. and Schantz, P.M. (2009) Echinococcosis: a review. Int. J. Infect. Dis. 13, 125–133 31 Bruzinskaite, R. et al. (2007) Alveolar echinococcosis, Lithuania. Emerg. Infect. Dis. 13, 1618–1619 32 Keis, J. et al. (2007) Current trends in echinococcosis in Latvia. Int. J. Antimicrob. Agents 29, S122–S123 33 Schweiger, A. et al. (2007) Human alveolar echinococcosis after fox population increase, Switzerland. Emerg. Infect. Dis. 13, 878–882 34 Kern, P. et al. (2004) Risk factors for alveolar echinococcosis in humans. Emerg. Infect. Dis. 10, 2088–2093 35 Stehr-Green, J.K. et al. (1988) Risk factors for infection with Echinococcus multilocularis in Alaska. Am. J. Trop. Med. Hyg. 38, 380–385 36 Kreidl, P. et al. (1998) Domestic pets as risk factors for alveolar hydatid disease in Austria. Am. J. Epidemiol. 147, 978–981 37 Yamamoto, N. et al. (2001) Risk factors for human echinococcosis: a case-control study in Hokkaido, Japan. Ann. Trop. Med. Parasitol. 95, 689–696 38 Eckert, J. et al. (2000) Echinococcosis: an emerging or re-emerging zoonosis? Int. J. Parasitol. 30, 1288–1294 39 Knapp, J. et al. (2007) Assessment of the use of microsatellite polymorphism analysis for improving spatial distribution tracking of Echinococcus multilocularis. J. Clin. Microbiol. 45, 2943–2950 40 Yamasaki, H. et al. (2008) Genetic analysis of Echinococcus multilocularis originating from a patient with alveolar echinococcosis occuring in Minnesota in 1977. Am. J. Trop. Med. Hyg. 79, 245–247 41 Hildreth, M.B. et al. (2000) Failure to identify alveolar echinococcosis in trappers from South Dakota despite high prevalence of Echinococcus multilocularis in wild canids. J. Parasitol. 86, 75–77 42 European Food Safety Authority (2010) The community summary report on trends and sources of zoonoses, zoonotic agents and foodborne outbreaks in the European Union in 2008. EFSA J. 8, 1496

Review 43 Bristow, B.N. et al. (2012) Human echinococcosis mortality in the United States, 1990–2007. PLoS Negl. Trop. Dis. 6, e1524 44 Bagrade, G. et al. (2011) Echinococcus multilocularis is a frequent parasite of red foxes (Vulpes vulpes) in Latvia. Helminthologia 45, 154–161 45 Knapp, J. et al. (2008) Genetic diversity of Echinococcus multilocularis on a local scale. Infect. Genet. Evol. 8, 367–373 46 Peregrine, A.S. et al. (2012) Alveolar hydatid disease (Echinococcus multilocularis) in the liver of a Canadian dog in British Columbia, a newly endemic region. Can. Vet. J. (in press) 47 Kamler, J.F. and Ballard, W.B. (2002) A review of native and nonnative red foxes in North America. Wildlife Soc. Bull. 30, 370–379 48 Cowan, I.M. and Guiguet, C.J. (1965) The Mammals of British Columbia, British Columbia Provincial Museum 49 Eckert, J. and Deplazes, P. (2004) Biological, epidemiological, and clinical aspects of echinococcosis, a zoonosis of increasing concern. Clin. Microbiol. Rev. 17, 107–135 50 Tsukada, H. et al. (2000) Preliminary study on the role of red foxes in Echinococcus multilocularis transmission in the urban area of Sapporo, Japan. Parasitology 120, 423–428 51 Wang, Q. et al. (2007) Impact of overgrazing on the transmission of Echinococcus multilocularis in Tibetan pastoral communities of Sichuan Province, China. Chin. Med. J. 120, 237–242 52 Giraudoux, P. et al. (2006) Transmission ecology of Echinococcus multilocularis: what are the ranges of parasite stability among various host communities in China? Parasitol. Int. 55, S237–S246 53 Davidson, R.K. and Robertson, L.J. (2012) European pet travel: misleading information from veterinarians and government agencies. Zoonoses and Public Health (in press) 54 Norwegian Scientific Committee for Food Safety (2012) Assessment of Risk of Introduction and Establishment of Echinococcus multilocularis to Mainland Norway (Robertson, L. et al., eds), Vitenskapskomitteen for Mattrygghet, http://vkm.no/dav/d35674e4f0.pdf, ISBN - 978-828259-043-3 55 Saeed, I. et al. (2006) Helminths of red foxes (Vulpes vulpes) in Denmark. Vet. Parasitol. 139, 168–179 56 Torgerson, P.R. and Craig, P.S. (2009) Risk assessment of importation of dogs infected with Echinococcus multilocularis into the UK. Vet. Rec. 165, 366–368 57 LAV (2011) Dati Traffico Cucciolo – Riepilogo Degli Ultimi due Anni da Fonti di Agenzie e Organi di Stampa a Cura Della LAV, Italian Ministry of Foreign Affairs 58 Seddon, P.J. et al. (2007) Developing the science of reintroduction biology. Conservation Biol. 21, 303–312 59 European Food Safety Authority (2011) The European Union summary report on trends and sources of zoonoses, zoonotic agents and foodborne outbreaks in 2009. EFSA J. 9, 2090, http://dx.doi.org/10.2903/ j.efsa.2011.2090 60 Hegglin, D. et al. (2008) Survey on public knowledge about Echinococcus multilocularis in four European countries: need for proactive information. BMC Public Health 8, 247 61 Vial, F. and Donnelly, C.A. (2012) Localised reactive badger culling increases risk of bovine tuberculosis in nearby cattle herds. Biol. Lett. 8, 50–53 62 Baker, P.J. et al. (2002) Effect of British hunting ban on fox numbers. Nature 419, 34 63 Tsukada, H. et al. (2002) Potential remedy against Echinococcus multilocularis in wild red foxes using baits with anthelmintic distributed around fox breeding dens in Hokkaido, Japan. Parasitology 125, 119–129 64 Romig, T. et al. (2007) Impact of praziquantel baiting on intestinal helminths of foxes in southwestern Germany. Helminthologia 44, 137–144 65 Ko¨nig, A. et al. (2008) Integrated-baiting concept against Echinococcus multilocularis in foxes is successful in southern Bavaria, Germany. Eur. J. Wildl. Res. 54, 439–447 66 Hegglin, D. et al. (2003) Anthelmintic baiting of foxes against urban contamination with Echinococcus multilocularis. Emerg. Infect. Dis. 9, 1266–1272 67 Hegglin, D. and Deplazes, P. (2008) Control strategy for Echinococcus multilocularis. Emerg. Infect. Dis. 14, 1626–1628 68 Rausch, R.L. et al. (1990) The ecology of Echinococcus multilocularis (Cestoda: Taeniidae) on St Lawrence Island, Alaska. II. Helminth

Trends in Parasitology June 2012, Vol. 28, No. 6

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70

71

72

73 74 75

76

77 78 79

80 81 82

83

84

85 86 87

88

89

90

91

populations in the definitive host. Annales de Parasitologie Humaine et Compare´e 65, 131–140 DEFRA (2010) The Change in Likelihood of Echinococcus multilocularis (Alveolar Echinococcosis) Introduction into the United Kingdom as a Consequence of Adopting Existing Harmonised Community Rules for the Non-commercial Movements of Pet Animals (Version 2.0 edn) (Toth, B. et al., eds), pp. 1–29, DEFRA. Kazacos, R. (2003) Cystic and alveolar hydatid disease caused by Echinococcus species in the contiguous United States. Compend. Contin. Educ. Pract. Vet. (North America Edition edn), Princeton Junction, N.J.: Veterinary Learning Systems 25, 16–20 Rausch, R. (1956) Studies on the helminth fauna of Alaska. XXX. The occurrence of Echinococcus multilocularis Leuckart, 1863, on the mainland of Alaska. Am. J. Trop. Med. Hyg. 5, 1086–1092 Rausch, R.L. (1967) On the ecology and distribution of Echinococcus spp. (Cestoda: Taeniidae), and characteristics of their development in the intermediate host. Annales de Parasitologie Humaine et Compare´e 42, 19–63 Eaton, R.D. and Secord, D.C. (1979) Some intestinal parasites of Arctic fox, Banks Island, NWT. Can. J. Comp. Med. 43, 229–230 Manfredi, M.T. et al. (2002) Echinococcus multilocularis infection in red foxes in Italy. Vet. Rec. 150, 757 Sre´ter, T. et al. (2003) Echinococcus multilocularis an emerging pathogen in Hungary and Central Eastern Europe. Emerg. Infect. Dis. 9, 384 Casulli, A. et al. (2005) Echinococcus multilocularis in red foxes (Vulpes vulpes) of the Italian Alpine region: is there a focus of autochthonous transmission? Int. J. Parasitol. 35, 1079–1083 Moks, E. et al. (2005) Echinococcus multilocularis in Estonia. Emerg. Infect. Dis. 11, 1973–1974 Rataj, A.V. et al. (2010) Echinococcus multilocularis in the red fox (Vulpes vulpes) in Slovenia. Eur. J. Wildl. Res. 56, 819–822 Wahlstro¨m, H. et al. (2011) Combining information from surveys of several species to estimate the probability of freedom from Echinococcus multilocularis in Sweden, Finland and mainland Norway. Acta Vet. Scand. 53, 9 http://dx.doi.org/10.1186/1751-014753-9 Craig, P.S. (2006) Epidemiology of human alveolar echinococcosis in China. Parasitol. Int. 55, S221–S225 Vuitton, D.A. et al. (2003) Epidemiology of alveolar echinococcosis with particular reference to China and Europe. Parasitology 127, S87–S107 Nakao, M. et al. (2010) State-of-the-art Echinococcus and Taenia: phylogenetic taxonomy of human-pathogenic tapeworms and its application to molecular diagnosis. Infect. Genet. Evol. 10, 444–452 Shimalov, V. and Shimalov, V. (2002) Helminth fauna of the red fox (Vulpes vulpes Linnaeus, 1758) in southern Belarus. Parasitol. Res. 89, 77–78 Kamiya, H. et al. (2003) A red fox, Vulpes vulpes shrencki, infected with Echinococcus multilocularis was introduced from Hokkaido Island, where E. multilocularis is endemic, to Aomori, northern part of mainland Japan. Jpn. J. Infect. Dis. 56, 180–181 Jenkins, D.J. et al. (2005) Emergence/re-emergence of Echinococcus sp. – a global update. Int. J. Parasitol. 35, 1205–1219 Shaikenov, B. (2006) Distribution and ecology of Echinococcus multilocularis in Central Asia. Parasitol. Int. 55, S213–S219 Vuitton, D.A. et al. (2011) A historical view of alveolar echinococcosis, 160 years after the first discovery of the first case in humans: part 1. What have we learnt on the distribution of the disease and on its parasitic agent? Chin. Med. J. 124, 2943–2953 Nonaka, N. et al. (2009) A vague understanding of the biology and epidemiology of echinococcosis by dog owners in Hokkaido, an endemic island for Echinococcus multilocularis in Japan. J. Vet. Med. Sci. 71, 105–107 Knapp, J. et al. (2012) Echinococcus multilocularis in Svalbard, Norway: microsatellite genotyping to investigate the origin of a highly focal contamination. Infect. Genet. Evol. http://dx.doi.org/ 10.1016/jmeegid.2012.03.008 Stien, A. et al. (2010) Intestinal parasites of the Arctic fox in relation to the abundance and distribution of intermediate hosts. Parasitology 137, 149–157 Fuglei, E. et al. (2008) Spatial distribution of Echinococcus multilocularis, Svalbard, Norway. Emerg. Infect. Dis. 14, 73–75

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