Unexpected diversity in northern Europe: trematodes from salmonid fishes in Iceland with two new species of Crepidostomum Braun, 1900.

In 2018 and 2019, salmonid fishes, Salmo trutta L. and Salvelinus alpinus (L.) from lakes in Iceland were assessed for trematodes during a parasitological examination. Combined morphological and molecular analyses revealed the presence of four trematode species, two of which were previously known to parasitise salmonids in Iceland, Crepidostomum farionis (Müller, 1780) and Phyllodistomum umblae (Fabricius, 1780), and the two remaining species were recognised as new to science. Morphologically and genetically, Crepidostomum brinkmanni n. sp. and C. pseudofarionis n. sp. are closely related to two European species, namely C. metoecus and C. farionis. However, C. brinkmanni n. sp. is distinct by the position of maximum body width and arrangement of vitelline follicles; C. pseudofarionis n. sp. is distinct by its stout body, position of maximum body width, size of muscular papillae relative to oral sucker and the anterior extent of vitelline follicles. The new species were previously molecularly detected in their intermediate and definitive hosts in Norway and Ukraine, but their sequences were not supplemented with any morphological characterisation. In the present study, we provide detailed morphological descriptions and molecular sequences (28S rDNA and ITS2) of the four species of trematodes detected in Iceland. The discovery of the two new species of Crepidostomum indicates that the trematode diversity in fishes in the north is higher than previously known; our finding doubles the species spectrum of fish trematodes for Iceland. The record of C. brinkmanni from Ukraine indicates that its distribution might not be limited to northern latitudes.

A new Eimeria species (Protozoa: Eimeriidae) from caribou in Ameralik, West Greenland.

Fecal samples of 11 calves shot in the Ameralik area, West Greenland, in August-September 2014 were examined for coccidian parasites. The calves belonged to a population of interbreeding indigenous caribou Rangifer tarandus groenlandicus and feral semi-domestic Norwegian reindeer Rangifer tarandus tarandus. Two coccidian species were found: Eimeria rangiferis and a coccidium that was identified and described as a new species. The latter's sporulated oocyst is spherical or slightly subspherical. Average size is 25.6 × 24.8 µm. The oocyst has two distinct walls. Wall thickness is ∼1.4 µm. The unicolored outer wall is brown, the inner wall is dark gray. The oocysts contain a small polar granule but are devoid of a microphyle. The oocysts enclose four ovoid-shaped sporocysts with a rounded end opposite to the Stieda body. The average size of sporocysts is 15.2 × 7.8 µm. Sporocysts contain a granular sporocyst residuum that forms a spherical cluster between the sporocysts, one large refractile body is present in each sporozoite. The spherical form easily distinguishes oocysts of the new species from the seven previously described eimerid species in R. tarandus. This is the first eimerid described as a new species to the sciences from caribou in the Nearctic.

Trichobilharzia anseri n. sp. (Schistosomatidae: Digenea), a new visceral species of avian schistosomes isolated from greylag goose (Anser anser L.) in Iceland and France.

Parasitological investigations carried out on birds in Iceland and France highlight the presence of four species of avian schistosomes from greylag geese (Anser anser L.): the european nasal species Trichobilharzia regenti and three visceral species, among which an unknown species isolated from blood vessels of the large intestine and liver. Morphological and molecular analyzes of different parasite stages (eggs, adults) revealed new species of Trichobilharzia genus ­ Trichobilharzia anseri sp. nov. Studies on host-parasite relationship under natural conditions, showed that the life-cycle includes the snail Radix balthica (syn. R. peregra) as intermediate host. The cercariae, already isolated in Iceland from two ponds of the Reykjavik capital area ­ the Family park and Tjörnin Lake ­ are the same as those isolated in 1999 by Kolárová et al. during the first study on Icelandic parasitic agents of cercarial dermatitis.

Fellow travellers: a concordance of colonization patterns between mice and men in the North Atlantic region.

BACKGROUND: House mice (Mus musculus) are commensals of humans and therefore their phylogeography can reflect human colonization and settlement patterns. Previous studies have linked the distribution of house mouse mitochondrial (mt) DNA clades to areas formerly occupied by the Norwegian Vikings in Norway and the British Isles. Norwegian Viking activity also extended further westwards in the North Atlantic with the settlement of Iceland, short-lived colonies in Greenland and a fleeting colony in Newfoundland in 1000 AD. Here we investigate whether house mouse mtDNA sequences reflect human history in these other regions as well. RESULTS: House mice samples from Iceland, whether from archaeological Viking Age material or from modern-day specimens, had an identical mtDNA haplotype to the clade previously linked with Norwegian Vikings. From mtDNA and microsatellite data, the modern-day Icelandic mice also share the low genetic diversity shown by their human hosts on Iceland. Viking Age mice from Greenland had an mtDNA haplotype deriving from the Icelandic haplotype, but the modern-day Greenlandic mice belong to an entirely different mtDNA clade. We found no genetic association between modern Newfoundland mice and the Icelandic/ancient Greenlandic mice (no ancient Newfoundland mice were available). The modern day Icelandic and Newfoundland mice belong to the subspecies M. m. domesticus, the Greenlandic mice to M. m. musculus. CONCLUSIONS: In the North Atlantic region, human settlement history over a thousand years is reflected remarkably by the mtDNA phylogeny of house mice. In Iceland, the mtDNA data show the arrival and continuity of the house mouse population to the present day, while in Greenland the data suggest the arrival, subsequent extinction and recolonization of house mice--in both places mirroring the history of the European human host populations. If house mice arrived in Newfoundland with the Viking settlers at all, then, like the humans, their presence was also fleeting and left no genetic trace. The continuity of mtDNA haplotype in Iceland over 1000 years illustrates that mtDNA can retain the signature of the ancestral house mouse founders. We also show that, in terms of genetic variability, house mouse populations may also track their host human populations.

Molecular diversity of Trichobilharzia franki in two intermediate hosts (Radix auricularia and Radix peregra): a complex of species.

Recently, the systematic use of the molecular approach as a complement to the other approaches (morphology, biology, life cycle) has brought help for the identification of species considered as different in the past to be regrouped and synonymised, and distinctions to be drawn between species similar at the morphological level. Among these species, we tried to clarify the situation of Trichobilharzia frankiMüller and Kimmig, 1994, species that today include more than 50 haplotypes notably coming from larval stages isolated from intermediate hosts belonging to gastropods of the Radix genus. Cercariae were isolated in France and Iceland from various molluscs, before being analyzed, with their hosts, by molecular analysis of various fields such as the D2 and ITS of the ribosomal DNA and the COX1 of mitochondrial DNA. We thus show the presence of two clades depending on the specificity of their intermediate host in which they were isolated (Radix auricularia or Radix peregra), thus allowing separation of the species T. franki that had been described in the past as a probable new species.

Methodical approaches in the identification of areas with a potential risk of infection by bird schistosomes causing cercarial dermatitis.

Larval stages (cercariae) of schistosomatid flukes represent the causative agents of swimmer's itch (cercarial dermatitis), a waterborne allergic disease. Cercariae of bird schistosomes are the most frequently reported agent. Recent studies on parasite behaviour in mammals showed that infections by cercariae can be linked to more than skin syndromes. Despite the failure of complete development in mammals, bird schistosomes can escape from the skin and migrate transitorily in the hosts. These findings brought novel insights into the fate and potential pathogenic effect of the parasites in non-compatible hosts, including humans. Cercarial dermatitis occurs globally and recently is considered to be re-emerging; however, there are no data on the number of afflicted persons per year. This might be explained by a relatively low interest in human skin infections arising after bathing in fresh water. In addition, the real occurrence of bird schistosomes in the field is known only for a few areas. The paucity of epidemiological/biogeographical data is probably caused by difficulties associated with detection of the parasites in intermediate and definitive hosts. Therefore, based on personal experience and data available in the literature, we have summarized methodological approaches enabling the detection of bird schistosomes in various hosts and environments.

Trichinella nativa in Iceland: an example of Trichinella dispersion in a frigid zone.

In most Arctic and subarctic regions, Trichinella nativa is a common zoonotic pathogen circulating among wild carnivores. The polar bear (Ursus maritimus) is one of the most important reservoirs for T. nativa in frigid zones. In Iceland, Trichinella infection has never been detected in the local wildlife, despite the presence of one of the host species, the arctic fox (Alopex lagopus). In 2008, one of two polar bears that had swum to Iceland's coast was found to have been infected with Trichinella sp. (8.5 larvae/g in the tongue, 6.8 larvae/g in the masseter and 4.4 larvae/g in the diaphragm); the larvae were identified as T. nativa. This is the second report of Trichinella infection in polar bears that reached the Icelandic coast. In the present work, we describe this case of infection and discuss the epidemiological features that have allowed T. nativa to spread in Arctic regions.

A review on swimmer's itch and the occurrence of bird schistosomes in Iceland.

In the past decade, swimmer's itch (SI) has repeatedly occurred in people who have been wading or bathing in ponds or lakes in Iceland where water birds and snails are abundant. Some of the affected sites were warmed by geothermal activity, and others were not. A search for the causative agent of SI, ocellate furcocercariae that have been found in Iceland only in Radix peregra snails, revealed an average infection prevalence of 1.4% (n = 12,432). Locally, infection rates commonly exceeded 6%, the highest value observed being 24.5%. A search for adult schistosomes in visceral organs and the nasal cavities of 110 water birds belonging to the orders Gaviiformes, Podicipediformes and Anseriformes revealed eggs, miracidia or adult stages of at least seven previously identifiable schistosome species in four anseriform bird species. A previously unknown species of schistosome, Allobilharzia visceralis, was detected in whooper swans (Cygnus cygnus), and classified in a new genus. In mallards (Anas platyrhynchos) a nasal Trichobilharzia sp. and the visceral schistosome T. franki were identified. In red-breasted merganser (Mergus serrator), distinct egg types belonging to two species of the genus Trichobilharzia have been found. In grey-lag goose (Anser anser) two different egg types were also found - a large Trichobilharzia sp. and small eggs of a Dendritobilharzia sp. Additionally, unidentified cercariae, probably belonging to a previously undescribed genus were detected in R. peregra in Oslandsstjörn. Taken together, the data obtained by morphological examination of eggs and recent DNA sequencing results, indicate that at least eight species of bird schistosomes occur in Iceland.

Bird schistosome diversity in Iceland: molecular evidence.

During the years 2002-2007, Icelandic freshwater snails and birds from different orders were examined for bird schistosomes. Only the snail Radix peregra and anatid birds proved to be infected. In total, 32 samples of bird schistosome cercariae from seven localities and four samples of adults of Anas platyrhynchos and Mergus serrator from two localities were used for sequencing of the internal transcibed spacer (ITS) region of rDNA. Based on the sequence and position in the phylogenetic tree, five species/genotypes of bird schistosomes were identified. Three of them correspond to the sequences in GenBank for Trichobilharzia franki, Trichobilharzia sp. JR-2007 from Anas penelope (isolates Pl7 and Pl10) and schistosomatid sp. JR-2004 from Physa fontinalis. The other two species/genotypes belong to the genus Trichobilharzia, but their further determination was not possible due to lack of data. All of these species/genotypes develop in R. peregra, probably the only suitable intermediate host species in Iceland. As T. franki and schistosomatid sp. JR-2004 were previously reported from other snail species, the findings from Iceland proved that, under some circumstances, bird schistosomes are able to adapt to a different snail species; some of them can even adapt to a snail belonging to a different gastropod family. High diversity of bird schistosomes in Iceland is probably linked with migratory flyways of birds, as several bird species from Iceland overwinter in western Europe as well as in North America.

Diversity of bird schistosomes in anseriform birds in Iceland based on egg measurements and egg morphology.

Radix balthica is the only freshwater mollusc in Iceland that has been found to be the intermediate host of ocellate furcocercariae. Infections are common. On average, 4.8% out of almost 7,000 snails examined during 2003-2006 were found to shed cercariae in late summer and autumn. Search for adult bird schistosome worms, eggs and miracidia in the intestines and in the nasal cavity of 110 water birds of the orders Gaviiformes (one species), Podicipediformes (one species) and Anseriformes (nine species) revealed 39 (35.5%) infected hosts. Exclusively, anseriform birds were infected. Based on morphological features and measurements of eggs, seven distinct bird schistosome species were detected in four of the bird species. Allobilharzia visceralis was found in 26.7% of the whooper swans Cygnus cygnus. In Anas platyrhynchos, the nasal Trichobilharzia sp. I (prevalence 73.3%) and the visceral Trichobilharzia sp. III (66.7%) were detected. In Mergus serrator, the distinct egg types of Trichobilharzia sp. IV and Trichobilharzia sp. V were found in 83.3% of examined birds. In Anser anser, also two different egg types were found: large eggs, referred to as Trichobilharzia sp. II (prevalence 54.2%), and the small eggs of Dendritobilharzia sp. (8.3%). Egg size and shape comparisons indicate that Trichobilharzia sp. III and T. franki might be the same species.

Two new Eimeria species (Protozoa: Eimeriidae) from wild rock ptarmigans, Lagopus muta islandorum, in Iceland.

One hundred rock ptarmigans, Lagopus muta islandorum (Faber, 1822), were collected in early October 2006 in northeastern Iceland and examined for coccidian parasites. Two Eimeria species were identified, and each is described as a new species. Sporulated oocysts of one species are ellipsoidal, 24.9 x 16.6 (19.5-30 x 14.5-19) microm. Oocysts have a small micropyle and a two-layered, smooth wall approximately 1.0 microm thick. An oocyst residuum is absent, but one to three polar granules are present. Sporocysts have a rounded end opposite a nipple-like Stieda body and are 14.3 x 6.3 (12-16.5 x 5.5-7) microm. Sporocysts contain one refractile body and a diffuse granular residuum; the entire contents of each sporocyst is enclosed by a thin membrane. Sporulated oocysts of the second eimerian are subspherical, 24.7 x 22.2 (20-28 x 18-24.5) microm. The oocysts are without a micropyle but with a two-layered wall, which is approximately 1.5 microm thick, with the outer layer having a rough surface texture. Oocyst residuum is absent, but one to two polar granules are present. Sporocysts have a rounded end opposite the nipple-like Stieda body atop a prominent sub-Stieda body and are 14.4 x 8.0 (12-15.5 x 6.5-9) microm. Sporocysts contain a diffuse granular residuum, and each sporozoite has two different-sized refractile bodies.

The third newly discovered Eimeria species (Protozoa: Eimeriidae) described from wild reindeer, Rangifer tarandus, in Iceland.

Fecal samples from 56 adult reindeer from eastern Iceland were examined for coccidian parasites. One Eimeria species was found in an 8-year-old male. Prevalence of infection was 1.8%; oocyst per gram (opg) value was 150. The coccidium was identified and described as a new species. The sporulated oocysts are ellipsoidal and average size is 30.0 x 21.1 microm. The oocyst has two distinct walls. Wall thickness is approximately 1.0 microm, and the outer wall, approximately four-fifths of total thickness, is generally smooth and appears bicoloured. The outermost portion is light blue, and the innermost portion, yellow to pale brown. The inner wall is dark brown. Oocysts contain a prominent polar granule but are devoid of a micropyle. Oocysts enclose four spindle-shaped sporocysts with a rounded end opposite to the Stieda body. The average size of sporocysts is 15.3 x 6.5 microm. Sporocysts contain a granular sporocyst residuum that usually forms a cluster between the sporozoites and one large refractile body in each sporozoite.

Description of a new Eimeria species and redescription of Eimeria mayeri (Protozoa: Eimeriidae) from wild reindeer Rangifer tarandus in Iceland.

Altogether, 195 fecal samples of reindeer calves (Rangifer tarandus) were collected from the ground in 3 distinct areas in eastern Iceland, where geographically isolated reindeer populations graze during the summer months. The samples were examined for coccidian parasites. Two species were found, and all infections were monospecific. Eimeria mayeri was found in calves in all sampling areas, with 1-4% prevalence and 450-167,700 oocysts per gram (opg). The sporulated oocyst lacks a polar granule but has an inconspicuous micropyle, and a small Stieda body is present on sporocysts, which are ovoid but not pointed as reported in the original description. The other coccidian, found in single calves in 2 of the 3 areas (prevalence 1 and 4%, 150 and 500 opg, respectively) is described here as a new species. The oocysts are ovoid, average 34.9 x 27.6 microm, and have 2 distinct walls. Wall thickness is approximately 1.9 microm, and the outer wall, approximately 3/4 of total thickness, is generally smooth and appears bicolored. The outermost portion is pale red and the innermost portion yellow to pale brown. The inner wall is grey to dark brown and separated from the outer wall by a dark brown line. Oocysts contain a prominent micropyle, approximately 5 microm, and enclose 4 spindle-shaped sporocysts, slightly pointed at the end opposite the Stieda body. Average size of sporocysts is 18.6 x 9.2 microm. Sporocysts contain granular sporocyst residuum and usually 2, sometimes 1, large refractile bodies in each sporozoite.

Mitochondrial DNA and microsatellite variation in the eider duck (Somateria mollissima) indicate stepwise postglacial colonization of Europe and limited current long-distance dispersal.

To unravel the postglacial colonization history and the current intercolony dispersal in the common eider, Somateria mollissima, we analysed genetic variation at a part of the mitochondrial control region and five unlinked autosomal microsatellite loci in 175 eiders from 11 breeding colonies, covering the entire European distribution range of this species. As a result of extreme female philopatry, mitochondrial DNA differentiation is substantial both among local colonies and among distant geographical regions. Our study further corroborates the previous hypothesis of a single Pleistocene refugium for European eiders. A nested clade analysis on mitochondrial haplotypes suggests that (i) the Baltic Sea eider population is genetically closest to a presumably ancestral population and that (ii) the postglacial recolonization progressed in a stepwise fashion via the North Sea region and the Faroe Islands to Iceland. Current long-distance dispersal is limited. Differentiation among colonies is much less pronounced at microsatellite loci. The geographical pattern of this nuclear genetic variation is to a large extent explained by isolation by distance. As female dispersal is very limited, the geographical pattern of nuclear variation is probably explained by male-mediated gene flow among breeding colonies. Our study provides genetic evidence for the assumed prominent postglacial colonization route shaping the present terrestrial fauna of the North Atlantic islands Iceland and the Faroes. It suggests that this colonization had been a stepwise process originating in continental Europe. It is the first molecular study on eider duck populations covering their entire European distribution range.

[The tropical rat mite Ornithonyssus bacoti attacks humans in Iceland.].

In the summer of 2001 the obligate, intermittent tropical rat mite Ornithonyssus bacoti attacked humans in an Icelandic household where infected Mongolian gerbils (Meriones unguiculatus), bought in a local pet shop, had been kept for few months. After a rapid proliferation the mite started attacking the humans living in the house. A boy sharing room with the pets suffered from extensive dermatitis. Optimal conditions for O. bacoti are at 24-26 degrees C and a relative humidity of 47%. Similar conditions frequently occur indoors in Icelandic premises. Therefore, if O. bacoti has been noticed indoors, necessary measures should be undertaken to immediately eliminate the pest.

Digeneans from intertidal molluscs of SW Iceland.

The fauna of digenean daughter-sporocysts, rediae, cercariae and metacercariae infecting molluscs Littorina spp., Onoba aculeus. Nucella lapillus and Epheria vincta has been studied in the Skerjafjordur and Grindavik regions of SW Iceland. In total, intramolluscan stages of 19 digenean species were recorded; 14 of them are new for Iceland and one of them, a microphallid named Cercaria islandica I, was unknown. A description of this new microphallid cercaria is provided. In addition, the identification and separation of the intramolluscan stages of some microphallid, renicolid and echinostomatid species are discussed. Consideration is given to difficulties encountered when identifying digenean species found on the coasts of European countries. Problems have arisen largely because larval and adult stages have been described and named independently and in isolation, synonyms are common and many "definitive" descriptions are inadequate or incomplete.

Schistosome cercariae as the causative agent of swimmer's itch in Iceland.

During late summer in 1995 to 1997, repeated outbreaks of maculopapular skin eruptions were noted on the legs of children after wading in the pond in the Family Park in Laugardalur, Reykjavík, Iceland. Clinical symptoms developing on the legs resembled those of cercarial dermatitis. An examination of Lymnaea peregra snails from this pond and from the adjacent Lake Tjornin resulted in detection of previously undescribed schistosome cercariae. This is the first report of schistosomes in Iceland and also the most northern occurrence of these parasites in Europe.

Levels and enantiomeric ratios of alpha-HCH, oxychlordane, and PCB 149 in blubber of harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) from Iceland and further species.

The chiral stationary phase beta-TBDM (35% heptakis(6-O-tert.-butyldimethylsilyl-2,3-di-O-methyl)-beta-cyc lod extrin in OV-1701) was applied to study the enantioenrichment of alpha-HCH, oxychlordane, and PCB 149 in blubber of two seal species from Iceland by gas chromatography with electron capture detection. The examined harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) showed alpha-HCH enantiomeric ratios (ER) > 1. The ER of PCB 149 was comparable in the two species from Iceland but for oxychlordane ER < 1 was observed in harbour seals while the oxychlordane ER in grey seals was > 1. In blubber of Weddell seals (Leptonychotes Weddelli) from the Antarctic we determined an alpha-HCH ER < 1 which is in contrast to the Icelandic seal species and a sample from Lake Baikal.

[On the biology of the pinworm.].

Pinworm Enterobius spp. has probably been an endemic parasite in humans in Iceland since the colonization of the country more than 1100 years ago. A recent survey on pinworm infections in children in playschools indicated that the pinworm is quite common. The results are published in another article in this issue. In this contribution general knowledge on the biology of the parasite (taxonomy, morphology, distribution, life-cycle, transmission, diagnosis and treatment) is reviewed. Recently, dozens of male pinworms found in a stool sample were identified as Enterobius gregorii. Since no other species identifications have been made in Iceland so far, it is not known if the other pinworm species E. vermicularis also occurs in Iceland.

Histological, histochemical, and fine structural observations on the lymph node of the common seal (Phoca vitulina) and the grey seal (Halichoerus grypus).

BACKGROUND: The recent seal death epizootic prompted interest in their immune system, for which no current morphological data were available. METHODS: Lymph nodes from adult harbor seals (Phoca vitulina) and grey seals (Halichoerus grypus) were investigated by light microscopy, electron microscopy, and lectin histochemistry. RESULTS: No significant differences in the lymph node morphology were found between the two species, and the overall organization of the nodes comprises of capsule, trabeculae, cortex, paracortex, and medulla. Capsule and trabeculae are composed of tightly packed collagen and elastic fibrils and are rich in fibroblasts, myofibroblasts, and smooth muscle cells. Unmyelinated nerve fibers are common. The cortex contains numerous secondary follicles with well-developed germinal centers and paracortical areas with high endothelial venules. Antigen-presenting cells and phagocytic macrophages were abundantly present. The medullary cords contain numerous plasma cells. Fibroblastic reticulum cells are common throughout the parenchyma and transverse the sinus. Marginal, radial, and medullary sinuses are lined by littoral cells. The visceral lining of the sinuses is marked by macrophages and by numerous mast cells. CONCLUSIONS: The morphology of seal lymph nodes does not differ significantly from that of terrestrial mammals. Earlier functional conclusions concerning seal lymph nodes are substantiated by this morphological study.