Introduction
This article surveys reports of human infection with parasitic helminths in the global Arctic and sub-Arctic region, northwards from a latitude of approximately 60°N, published in the period 2001–2024. We use 60°N to focus on the northernmost part of the inhabited world as it has relatively sparse literature compared to other regions of the world.
Previous review articles in the literature have concentrated on particular helminth genus or geographical region, for example: Trichinellosis (Ozeretskovskaya et al., Reference Ozeretskovskaya, Mikhailova, Sabgaida and Dovgalev2005; Oksanen et al., Reference Oksanen, Karssin, Berg, Koch, Jokelainen, Sharma, Jenkins and Loginova2022); Echinococcus (Davidson et al., Reference Davidson, Lavikainen, Konyaev, Schurer, Miller, Oksanen, Skírnisson and Jenkins2016); Dibothriocephalus (Kralova-Hromadova et al., Reference Kralova-Hromadova, Radacovska, Cisovska Bazsalovicsova and Kuchta2021; Kuchta et al., Reference Kuchta, Radacovska, Cisovska Bazsalovicsova and Kralova-Hromadova2023); the Americas (Jenkins et al., Reference Jenkins, Castrodale, De Rosemond, Dixon, Elmore, Gesy, Hoberg, Polley, Schurer, Simard and Thompson2013). Those articles have also incorporated historical perspectives. Generally, there has been a decline in human helminth infections in this region during the 20th century, due to public health campaigns and specific control and monitoring programmes. These include for E. granulosus in Iceland (Saarma et al., Reference Saarma, Skirnisson, Bjornsdottir, Laurimae and Kinkar2023) and Finland (Hirvelä-Koski et al., Reference Hirvelä-Koski, Haukisalmi, Kilpelä, Nylund and Koski2003; Oksanen and Lavikainen, Reference Oksanen and Lavikainen2015) and E. multilocularis surveillance in Nordic countries (Wahlström et al., Reference Wahlström, Enemark, Davidson and Oksanen2015).
Here, by applying a 21st-century timeframe and a global lens, we concentrate on more recent reports to highlight the ongoing risk of human infection.
Methods
Search terms comprising genus name and geographical region, e.g. [‘Trichinella’ AND ‘Human’ AND ‘Greenland’] were searched on PubMed, Web of Science and Google Scholar for publications dated from 2001 onwards. There were no language restrictions. Excluded were articles in which the source of infection was identified or suspected by those publications’ authors as below 60°N.
Results
Of the articles identified for inclusion herein, the majority (n = 27) were primary reports of helminth infection that were either fully accessible to us online or in a few cases only the Abstract. There were a smaller number of publications that compiled national sources of data and/or unpublished reports for which the primary data were not readily attainable.
The helminth genera comprised nematodes Trichinella, Toxocara, Anisakis, Pseudoterranova, cestodes Echinococcus, Dibothriocephalus and trematode Opisthorchis, Trichobilharzia. All are zoonotic and, with the exception of Trichobilharzia, are acquired by ingestion of infective helminth propagules from undercooked game (mammal or fish) or by exposure to materials contaminated by animal faeces (Benesh et al., Reference Benesh, Parker and Chubb2021). The identified articles concentrated on a single genus or considered up to 3 genera.
Geographic locations in the Americas were in Alaska, Canada and Greenland (Kalaallit Nunaat), and in Eurasia were in Iceland, Norway, Finland and Russian Federation (Figure 1). In the primary reports, infections were identified by serology in community surveys (Table 1) or in individual cases (sometimes with parasitological or molecular demonstration), or as part of outbreaks (principally of Trichinella, Table 2).
Figure 1. Indicative locations of the studies surveyed herein. Encircled regions show the geographical scope of regional studies. Dashed line represents latitude 60°N.
Table 1. Geographical distribution of seroprevalence studies surveyed herein
a See text.
Table 2. Trichinellosis outbreak clusters surveyed herein
The highest number of articles were on Trichinella, followed by Toxocara and Echinococcus. Articles on the trematodes Opisthorchis and Trichobilharzia referred only to Eurasia, whereas the other genera were represented by articles referring to both Eurasia and the Americas.
In the following sections, each genus is considered in turn, with a brief description of propagule infection followed by the reports according to geographical setting.
Nematodes
Trichinella spp.
Consumption of inadequately cooked game meat containing parasite larvae can lead to diarrhoea, fever, myalgia, facial oedema, eosinophilia and elevated levels of muscle enzymes. The predominant regional taxon of this genus is encapsulated T. nativa, viable at low (frozen) temperatures (Pozio, Reference Pozio2016).
Americas. A serosurvey among bird-hunting populations of southern Alaska sampled in 2007–2008 found 5% seropositivity, although no specific source of infection was proposed (Miernyk et al., Reference Miernyk, Bruden, Parkinson, Hurlburt, Klejka, Berner, Stoddard, Handali, Wilkins, Kersh, Fitzpatrick, Drebot, Priest, Pappert, Petersen, Teshale, Hennessy and Bruce2019). However, outbreaks of trichinellosis related to the consumption of walrus (Odobenus rosmarus) were identified in 2016 and 2017 in the Norton Sound area of western Alaska. In the 2016 outbreak, 5 members of the same family were affected; the following year an outbreak was suspected in a separate community, involving 5 neighbours who had shared walrus meat. In both outbreaks, the incriminated meat was not available for testing, but stored (frozen) meat from the household of the 2017 outbreak was identified by polymerase chain reaction (PCR) to contain T. nativa (Springer et al., Reference Springer, Casillas, Helfrich, Mocan, Smith, Arriaga, Mixson, Castrodale and McLaughlin2017).
A study in 2004, part of a Canadian health survey in the northern Quebec region of Nunavik, reported a seroprevalence of ≤1% for the 14 sites as a whole (Messier et al., Reference Messier, Levesque, Proulx, Rochette, Serhir, Couillard, Ward, Libman, Dewailly and Dery2012). In contrast, a study conducted in 2007 and 2008 across coastal regions further north in Nunavut, as part of the International Polar Year Inuit Health Survey, reported a combined seroprevalence of 18.6% from >30 communities; these remote far northern study populations were reached by sea or air (Goyette et al., Reference Goyette, Cao, Libman, Ndao and Ward2014). An analysis of Canadian hospital admissions between 2001 and 2005 revealed that there was a much higher incidence in Nunavut and Nunavik together than in the rest of Canada combined (Gilbert et al., Reference Gilbert, Dare, Libman, Muchaal and Ogden2010).
Outbreak clusters in northern Canada reported since 2001 have been associated with coastal communities. In 1997, the implementation of a novel control programme including PCR identification of T. nativa in walrus meat samples and community engagement prevented a larger outbreak in Puvirnituq and Inukjuak (west coast of Nunavik) (Proulx et al., Reference Proulx, Maclean, Gyorkos, Leclair, Richter, Serhir, Forbes and Gajadhar2002). In 1999, 7 individuals, who had eaten raw walrus meat a few weeks previously, presented at a health centre in Qikiqtarjuag (eastern coast of Nunavut) with symptoms including diarrhoea, abdominal pain, rash and swelling. All were found to have high levels of anti-Trichinella antibodies and eosinophilia (Serhir et al., Reference Serhir, Maclean, Healey, Segal and Forbes2001). In 2009, a cluster in a group of sailors returning to France after exploring the Northwest passage on 2 different boats was considered to be most likely caused by consumption of frozen meat of grizzly bear (Ursus arctos) around Cambridge Bay (Iqaluktuuttiaq), Victoria Island, Nunavut. Prior to definite diagnosis, 2 of the sailors while still on-board experienced influenza-like symptoms (Houzé et al., Reference Houzé, Ancelle, Matra, Boceno, Carlier, Gajadhar and Dupouy-Camet2009). In 2013, another outbreak in Inukjuak involved 18 individuals across 15 different households, notable as most of the cases were adult women and also as the investigators were not able to identify a specific event or food source as a cause, although distributed meat of polar bear (Ursus maritimus) was considered the most likely (Ducrocq et al., Reference Ducrocq, Proulx, Simard, Levesque, Iqaluk, Elijassiapik, Ningiuk, Perkins, Jacques and Lemire2020).
A seroprevalence study comparing samples from various settlements predominantly in western Greenland archived between 1979–1981 and 1998–2004 identified (i) game meat consumption as the main risk factor for infection and (ii) a declining trend in seropositivity between the 2 time periods, likely due to the increased consumption of industrially produced food (Møller, Reference Møller2007). A seroprevalence of 1.1% was found from a 2001 survey among children under 14 years of age in western Greenlandic settlements (Møller et al., Reference Møller, Krause, Koch, Melbye, Kapel and Petersen2007). Similarly, a 2004 sampling among game hunting communities in eastern Greenland revealed an increase in seropositivity according to age, 1.4% vs 7.5% in participants aged under or over 40 respectively; seroprevalence for the ⩾60 years age group alone was 12%. ‘Occupation hunter/fisherman’ and ‘polar bear meat consumption’ were identified as significant risk factors (Møller et al., Reference Møller, Koch, Petersen, Hjuler, Kapel, Andersen and Melbye2010).
As elsewhere in the Americas, outbreak clusters have been recognized in Greenland in recent decades. In 2001, a cluster associated with consumption of game meat, suspected to be walrus, was identified near Aasiaat in west Greenland. Serological confirmation by ELISA and Western blot was achieved in 4 of the 6 cases initially; 1 of the 2 seronegative cases sero-converted when tested a year later, the authors considered this due to new infection (Møller et al., Reference Møller, Petersen, Kapel, Melbye and Koch2005). In a later outbreak, 3 travellers returning to France in 2016 presented at a Paris hospital with symptoms including myalgia, diarrhoea, with elevated eosinophilia and creatinine kinase levels. They had consumed meat of polar bear in eastern Greenland a few weeks before; trichinellosis was confirmed by ELISA and Western blotting (Dupouy-Camet et al., Reference Dupouy-Camet, Yera, Dahane, Bouthry and Kapel2016).
Eurasia. In the Russian Federation, sampling in 2007 from Viljujsk city, Sakha/Yakutia, north-eastern Siberia, reported 4.4% seroprevalence by ELISA (Magnaval et al., Reference Magnaval, Tolou, Gibert, Innokentiev, Laborde, Melnichuk, Grandadam, Crubezy and Alekseev2011). From sampling in 2 coastal settlements in Chukotka on the Arctic coast of the Bering Sea in 2010 and 2011, 24.3% seroprevalence was found by ELISA using in-house-generated T. nativa excretory–secretory antigen, with important sources of infection being meat of walrus and seal (Phoca) (Uspensky et al., Reference Uspensky, Bukina, Odoevskaya, Movsesyan and Voronin2019). A serosurvey in 2018 in rural areas of Central Sakha/Yakutia used commercial ELISA kit to detect 2.2% seroprevalence; the authors also assessed IgG against E. granulosus and T. canis, as described in the sections below. However, in that study, none of the 3 helminths had correlations with possible exposure variables identified (Nakhodkin et al., Reference Nakhodkin, Pshennikova, Dyachkovskaya, Barashkov, Nikanorova, Teryutin, Melnichuk, Crubezy, Fedorova and Magnaval2019).
A listing of outbreaks within the Russian Federation between 1996 and 2002, compiled from official sources, cites an outbreak involving 10 cases in Yamal-Nenets in north-western Siberia caused by consumption of the meat of the brown bear (Ursus arctos) (Ozeretskovskaya et al., Reference Ozeretskovskaya, Mikhailova, Sabgaida and Dovgalev2005).
Toxocara spp.
Ingestion of embryonated eggs in material contaminated with dog or cat faeces results in the release of larvae that migrate in the human body, consequently, toxocariasis comprising several pictures (covert toxocariasis, visceral larva migrans, ocular or neurological toxocariasis) may occur.
Americas. The Canadian studies of Messier et al. and Goyette et al. described above reported 3.9% and 1.7% seroprevalence respectively for human toxocariasis using a commercial ELISA (Messier et al., Reference Messier, Levesque, Proulx, Rochette, Serhir, Couillard, Ward, Libman, Dewailly and Dery2012; Goyette et al., Reference Goyette, Cao, Libman, Ndao and Ward2014). Decrease in seropositivity associates with northerly latitude in Canada (Bradbury and Panicker, Reference Bradbury and Panicker2020).
Eurasia. Anti-Toxocara IgG4 seroprevalences of 17.5% and 8.0% in parents and offspring respectively were found as part of a Norwegian inter-generational study (overall 11.7%), identifying positive associations with allergic symptoms among the offspring. The authors described a soluble worm somatic antigen preparation for use in the ELISA (Jõgi et al., Reference Jõgi, Svanes, Siiak, Logan, Holloway, Igland, Johannessen, Levin, Real, Schlunssen, Horsnell and Bertelsen2018).
Seroprevalence has been reported from Sakha/Yakutia (Russian Federation). In a 2007 sampling, seroprevalence by Western blot of 4.4% was reported in a Northwestern area (Magnaval et al., Reference Magnaval, Tolou, Gibert, Innokentiev, Laborde, Melnichuk, Grandadam, Crubezy and Alekseev2011), although none was found in other settlements of the Far North (Magnaval et al., Reference Magnaval, Leparc-Goffart, Gibert, Gurieva, Outreville, Dyachkovskaya, Fabre, Fedorova, Nikolaeva, Dubois, Melnitchuk, Daviaud-Fabre, Marty, Alekseev and Crubezy2016). In line with this, a sampling in in 2007–2008 revealed 3% seroprevalence by commercial ELISA, among the lowest in the geographical range (south to north) of Russian regions examined (Akhmadishina et al., Reference Akhmadishina, Ruzina, Lukasheva, Kyuregyan, Mikhailov and Lukashev2020), and a 2018 sampling identified 1.1% seroprevalence (Nakhodkin et al., Reference Nakhodkin, Pshennikova, Dyachkovskaya, Barashkov, Nikanorova, Teryutin, Melnichuk, Crubezy, Fedorova and Magnaval2019).
Anisakids
Larvae of anisakid species such as Anisakis simplex and Pseudoterranova decipiens in muscle of undercooked marine fish are released by human stomach enzymes, leading to gastric or intestinal infection. Both locally acquired (Norway, Iceland, Greenland) and imported cases (from Alaska) have been reported.
Americas. The study of western Greenlandic settlements mentioned above for Trichinella also reported the first human arctic IgG against Anisakidae (Møller et al., Reference Møller, Krause, Koch, Melbye, Kapel and Petersen2007). In imported cases, anisakiasis was detected histologically within an inguinal hernia in a patient who had consumed raw salmon from a stream on a recent fishing trip to Alaska (Hope et al., Reference Hope, Smith-Chakmakova and Snyder2020). The first documented imported cases in Austria occurred in 2 travellers returning from an Alaskan fishing trip where they had consumed cold smoked salmon. Diagnosis was by specific antibody detection, the morphological and molecular identification of A. simplex s. str. larvae in the consumed salmon and of Anisakis DNA in the resected ileum of 1 of the patients (Auer et al., Reference Auer, Leskowschek, Engler, Leitner, Wentzel, Wolkerstorfer and Schneider2007).
Eurasia. In Norway, a chronic infection was identified by decreased A. simplex IgE serology following resection of an occluding duodenal tumour, and suggestive identification of a tubular sclerotic structure 1–2 mm in diameter. The authors reported the patient’s history of consumption of prepared saltwater fish (Eskesen et al., Reference Eskesen, Strand, Andersen, Rosseland, Hellum and Øa2001).
Between 2004 and 2020 in Iceland, 16 human cases of P. decipiens and 2 of A. simplex were identified in this island nation (Skírnisson, Reference Skírnisson2022). Among these, P. decipiens larvae were found in the throats of patients a few days after consumption of inadequately cooked catfish (Skírnisson, Reference Skírnisson2006).
Cestodes
Echinococcus spp.
Transmission is by ingestion of eggs in material contaminated with canid faeces (leading to hydatid cyst), or following contact with foxes (alveolar echinococcosis, AE).
Americas. Two documented human cases of E. granulosus cystic echinococcosis (CE) in Alaska were reported as having unusually severe presentations (Castrodale et al., Reference Castrodale, Beller, Wilson, Schantz, McManus, Zhang, Fallico and Sacco2002). The 2007–2008 sampling mentioned above (Miernyk et al., Reference Miernyk, Bruden, Parkinson, Hurlburt, Klejka, Berner, Stoddard, Handali, Wilkins, Kersh, Fitzpatrick, Drebot, Priest, Pappert, Petersen, Teshale, Hennessy and Bruce2019) reported 1.8% and 0.1% seroprevalences for E. granulosus and E. multilocularis, respectively.
The Canadian studies of Messier et al. and Goyette et al. described above reported 8.3% and 6.3% seroprevalence respectively for E. granulosus only (Messier et al., Reference Messier, Levesque, Proulx, Rochette, Serhir, Couillard, Ward, Libman, Dewailly and Dery2012; Goyette et al., Reference Goyette, Cao, Libman, Ndao and Ward2014). Analyses of Canadian hospital admissions have also been undertaken. One study of the years 2001–2005 revealed the incidence for echinococcosis increased with northerly latitude, the highest being from above 55°N. The type of echinococcosis (CE or AE) was not specified (Gilbert et al., Reference Gilbert, Dare, Libman, Muchaal and Ogden2010). A different analysis for year range 2000–2020 also found that Northwest Territories, Nunavut and Yukon together (all above 60°N) had a much higher risk of echinococcosis (relative risk 17.1; 95% confidence interval: 8.7–33.7) compared to more southerly Atlantic provinces, with Northwest Territories having the highest national risk and increase (6.3–9.1 cases/million) but decreases in Nunavut and Yukon (8.6–2.6 and 5.3–5.1 respectively/million). The number of identified cases of E. granulosus and E. multilocularis for Canada as a whole were given by those authors, but not specified geographically for each province (Khalid et al., Reference Khalid, Muchaal and Julien2024).
Eurasia. Sampling in 2012 in the Russian Federation identified 1.3% seroprevalence of AE in a study of 2 villages in the Verkhoyansk district (Far North Sakha/Yakutia) by ELISA using commercial soluble extract of E. granulosus protoscoleces and a second-tier Western blot using E. multilocularis whole larval extract for AE discrimination (Magnaval et al., Reference Magnaval, Leparc-Goffart, Gibert, Gurieva, Outreville, Dyachkovskaya, Fabre, Fedorova, Nikolaeva, Dubois, Melnitchuk, Daviaud-Fabre, Marty, Alekseev and Crubezy2016). A 2018 sampling in the same region reported 4.4% seroprevalence (Nakhodkin et al., Reference Nakhodkin, Pshennikova, Dyachkovskaya, Barashkov, Nikanorova, Teryutin, Melnichuk, Crubezy, Fedorova and Magnaval2019).
Dibothriocephalus spp.
Following ingestion of the plerocercoid from undercooked fish, adult worms may grow to several metres in length within the human host.
Americas. A report of traveller returning to Austria, who passed a 75 cm tapeworm segment in stool, was suspected to have been infected during an Alaskan fishing tour 14 months earlier. The otherwise asymptomatic patient, without weight loss, anaemia or eosinophilia, was treated successfully with a single dose of praziquantel (Stadlbauer et al., Reference Stadlbauer, Haberl, Langner, Krejs and Eherer2005).
Eurasia. A report of molecular typing of D. latus DNA included an infection from a Finnish patient, who reported having eaten a local fish meal in the southern coastal locality of Kotka (Wicht et al., Reference Wicht, Ruggeri-Bernardi, Yanagida, Nakao, Peduzzi and Ito2010).
An analysis of official reports and Russian-language sources revealed information according to region. North-western Russia: in Karelia nearly 300 cases between 2011 and 2013; in Arkhangelsk a decrease in incidence/100 000 from 6.99 to 2.74 between 2006 and 2017. Ural district: in Khanty-Mansi region 210 cases between 2020 and 2022. Siberia: incidence/100 000 in Evenk (548.8) and Taymyr Dolgano-Nenets (343.7) administrative regions were the highest nationally. Far East: in Sakha/Yakutia decrease in incidence to 112.2/100 000 by 2016 (Kuchta et al., Reference Kuchta, Radacovska, Cisovska Bazsalovicsova and Kralova-Hromadova2023). Molecular analysis of an adult worm expelled from a patient in the St Petersburg area allowed the identification of repetitive elements in the D. latus genome (Usmanova and Kazakov, Reference Usmanova and Kazakov2010).
Trematode
Opisthorchis spp.
Following ingestion of metacercaria from undercooked fish, adult worms live in human bile ducts, significantly increasing risk of cholangiocarcinoma in chronic infection.
Eurasia. Infection with O. felineus is endemic in many parts of Russian Federation, principally in Western Siberia. An analysis of official sources for 2011–2013 revealed the highest incidence in Khanty-Mansi and Yamal-Nenets regions (599.7 and 261.9 cases respectively/100 000/year). Approximately 30 000 new cases were diagnosed each year nationally (Fedorova et al., Reference Fedorova, Kovshirina, Kovshirina, Fedotova, Deev, Petrovskiy, Filimonov, Dmitrieva, Kudyakov, Saltykova and Ogorodova2017).
A familial outbreak in Israel was traced to imported fish eaten 10 days earlier that had been originally bought in Nizhnevartovsk, Khanty-Mansi region. Diagnosis was confirmed by identification of worm ova in patient stool, and presumed to be O. felineus due to high levels of endemicity in the region of origin (Yossepowitch et al., Reference Yossepowitch, Gotesman, Assous, Marva, Zimlichman and Dan2004).
Trichobilharzia spp.
These members of the Schistosomatidae family infect humans through skin penetration by the cercariae which emerge from the intermediate snail host. Cercarial dermatitis (‘swimmers itch’) is caused by zoonotic schistosomes which do not develop fully in humans. Following infection, a pruritic dermal maculopapular response develops.
Eurasia. In Iceland, outbreaks of cercarial dermatitis after infection by bird schistosome cercariae have been reported since 2000 (Skírnisson et al., Reference Skírnisson, Aldhoun and Kolárová2009). Two outbreaks occurred in a touristic geothermally heated brook in Landmannalaugar in the southern interior of the island in 2003 and 2004. The authors state that these were caused by increased numbers of Trichobilharzia schistosomes deriving from mallard (Anas platyrhynchos) ducklings and developing in Radix peregra snails (Skírnisson and Kolarova, Reference Skírnisson and Kolarova2005).
In a compilation of reports from Norway between 2001 and 2009, cercarial dermatitis was recorded in dozens of lakes throughout the length of that country (Soleng and Mehl, Reference Soleng and Mehl2011). The authors of that study identified Trichobilharzia franki cercariae shed from a R. auricularia snail in a sampling in 2008.
Discussion
The prevalence of neglected infectious diseases in Arctic and sub-Arctic communities may not always have been well considered in global disease burdens, due to factors such as the geographical and societal remoteness of such populations (Hotez, Reference Hotez2010).
Our intention here was to survey recent literature for a broad range of human helminths (nematode, cestode and trematode) to encompass the inhabited global region above 60°N. From fully accessible (online) primary reports, we could extract details including locations, sampling, and diagnostic tests. However, this was not always possible, as some articles referred to compiled national data (Ozeretskovskaya et al., Reference Ozeretskovskaya, Mikhailova, Sabgaida and Dovgalev2005; Gilbert et al., Reference Gilbert, Dare, Libman, Muchaal and Ogden2010; Fedorova et al., Reference Fedorova, Kovshirina, Kovshirina, Fedotova, Deev, Petrovskiy, Filimonov, Dmitrieva, Kudyakov, Saltykova and Ogorodova2017; Khalid et al., Reference Khalid, Muchaal and Julien2024; Skírnisson, Reference Skírnisson2022; Kuchta et al., Reference Kuchta, Radacovska, Cisovska Bazsalovicsova and Kralova-Hromadova2023) or only the abstract was accessible to us (e.g. Auer et al., Reference Auer, Leskowschek, Engler, Leitner, Wentzel, Wolkerstorfer and Schneider2007; Skírnisson, Reference Skírnisson2006).
Many of these studies used commercial ELISA tests to identify immunoglobulin G (IgG). Some authors acknowledged the possible limitations of the commercial ELISAs, such as used for Trichinella, including lack of specificity, and confounding longevity of IgG, as caveats (Messier et al., Reference Messier, Levesque, Proulx, Rochette, Serhir, Couillard, Ward, Libman, Dewailly and Dery2012; Goyette et al., Reference Goyette, Cao, Libman, Ndao and Ward2014). For Toxocara, ELISA or Western blot using T. canis excretory-secretory antigens do not discriminate between infection due to T. canis and that due to T. cati. Such considerations may also skew associations with risk factors. Therefore, the identification and characterization of outbreak clusters becomes of particular interest. Those described here principally relate to trichinellosis, for which the most literature was readily accessible, predominantly from the Americas. These demonstrate that transmission to humans is ongoing and therefore almost certainly under-reported due the isolation of hunting communities or mild or unrecognized symptoms.
Among reports in returning travellers, infections originated in the Americas (Alaska, Canada, Greenland). These articles reinforce the importance of travel history including food consumption, which may otherwise lead to misdiagnosis and delay appropriate treatment.
The helminths described in the current article are all zoonoses, which (with the exception of Trichobilharzia) require human exposure to undercooked game, or to materials contaminated by animal faeces. Thus, not only prevalence in the sylvatic environment but also human lifestyle are crucial for transmission. For example, in stark contrast to the increase in trichinellosis and echinococcosis with northerly latitude in Canada (Gilbert et al., Reference Gilbert, Dare, Libman, Muchaal and Ogden2010; Khalid et al., Reference Khalid, Muchaal and Julien2024), anti-Toxocara IgG seroprevalence showed the opposite trend in that country (Bradbury and Panicker, Reference Bradbury and Panicker2020) and in Russian Federation (Akhmadishina et al., Reference Akhmadishina, Ruzina, Lukasheva, Kyuregyan, Mikhailov and Lukashev2020), likely due to unfavourable environmental conditions for persistence of the mature infective embryonated egg and contact with humans.
Control programmes for E. granulosus (CE) have been successful in Iceland leading to eradication by 1979 (Saarma et al., Reference Saarma, Skirnisson, Bjornsdottir, Laurimae and Kinkar2023) and in human food-chain reindeer in Finland (Hirvelä-Koski et al., Reference Hirvelä-Koski, Haukisalmi, Kilpelä, Nylund and Koski2003; Oksanen and Lavikainen, Reference Oksanen and Lavikainen2015). For E. multilocularis (AE), surveillance in Nordic countries has been in place since its identification in a fox in Denmark in 2000 (Wahlström et al., Reference Wahlström, Enemark, Davidson and Oksanen2015). In this control context, the Nunavik Trichinellosis Prevention Program, implemented in the 1997 outbreak in Nunavik in northern Quebec (Proulx et al., Reference Proulx, Maclean, Gyorkos, Leclair, Richter, Serhir, Forbes and Gajadhar2002), succeeded in preventing any further local walrus-acquired outbreaks for more than decade, despite the ongoing identification of Trichinella-positive walrus meat (Larrat et al., Reference Larrat, Simard, Lair, Belanger and Proulx2012).
Climate change, i.e. increase in global temperatures, has a potential impact on helminth infections in this region. Higher ambient temperatures may favour O. felineus transmission in Siberia by increasing cercariae survival and the amount of (non-permafrost) habitat available to Bithynia snails (Sripa et al., Reference Sripa, Yurlova, Suwannatrai, Serbina, Tangkawattana, Sayasone and Varnakovida2025). The latter consideration is also applicable to soil-dwelling embryonated eggs of Toxocara. Anisakid range may also be extended in polar areas (Rokicki, Reference Rokicki2009), a zoonotic risk emphasized by the detection of these nematodes in Inuit fish and mammal food sources in the Canadian Far North (Pufall et al., Reference Pufall, Jones-Bitton, McEwen, Brown, Edge, Rokicki, Karpiej, Peregrine and Simard2012). We also note here the reports of cercarial dermatitis from lakes in northern Norway that experienced warm summers (Soleng and Mehl, Reference Soleng and Mehl2011).
Herein we have brought together information from published seroprevalence studies, outbreaks, imported cases and compilations of official sources of national data to highlight this extant challenge to human health in the global Arctic and sub-Arctic. As demonstrated by these 21st-century articles, helminth infections persist across this region, potentially posing a growing threat due to warming temperatures, so should not be overlooked in assessing the global impact on human disease burden. Future directions include the need for sustained research and public recognition of the ongoing risk, aided by the refinement of serological tests to improve specificity (subgenus level) in epidemiological studies, and the broader implementation of control programmes with crucial community engagement, taking a One Health approach.
Data availability statement
No novel datasets were generated or analysed for this article. All cited references were available online via public-access resources.
Acknowledgements
The map in Figure 1 and the Graphical Abstract was derived from https://d-maps.com/carte.php?num_car=3192&lang=en. We thank the reviewers for their comments that have improved the manuscript.
Author contributions
TB conceived the study, performed the literature search and wrote the article. MAM edited the article.
Financial support
This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
Competing interests
The authors declare there are no conflicts of interest.
Ethical standards
Not applicable.
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