Prosorhynchoides borealis Bartoli, Gibson & Bray, 2006 (Digenea: Bucephalidae) cercariae from Abra prismatica (Mollusca: Bivalvia) in Icelandic waters.

This paper reports the adult stage of Prosorhynchoides borealis (Digenea) from Lophius piscatorius in Icelandic waters and infections with the larval stages (sporocysts and cercariae) found for the first time in the bivalve Abra prismatica (Semelidae). The previously known first intermediate host was Abra alba (Semelidae). Ribosomal DNA sequencing studies on all three life stages of the parasite (cercariae, metacercariae, adults) were performed to confirm their identites. Morphometric measurements confirmed that the adult worms belong to the newly described species P. borealis. Prosorhynchoides borealis sporocysts filled with cercariae were found in 16% of A. prismatica bivalves sampled at depths between 34 and 93 m off South Iceland. Prevalence ranged from 0 to 44% between different localities. The parasite was found only in the larger bivalves. Extensive sporocyst infection in the haemocoel of the foot caused mechanical muscle damage with subsequent degeneration and necrosis. Other tissues, including the digestive gland, nephridia, gills and intestine, were less heavily infected. Only focal necrosis was observed in the digestive gland, nephridia and gills, and local atrophy in the intestine. Cercariae were also observed in the lumen of both the stomach and intestine. This is the first report of A. prismatica as an alternative first intermediate host for P. borealis. Ribosomal DNA sequence data reveals 100% homology in the data between cercariae, metacercariae and adult digeneans, supporting the morphological data suggesting that all stages belong to the same species.

Population genetics of Parascaris equorum based on DNA fingerprinting.

The large roundworm of horses, Parascaris equorum is considered ubiquitous in breeding operations, and is regarded as a most important helminth pathogen of foals. Over the past decade, this parasite has been reported increasingly resistant to anthelmintic drugs worldwide. This paper reports analysis of the population genetic structure of P. equorum. Adult parasites (n=194) collected from Sweden, Norway, Iceland, Germany, Brazil and the USA were investigated by amplified restriction fragment length polymorphism (AFLP) analysis. The genetic variation was low (Hj=0.12-0.4), for the global population of worms. This was accompanied by a weak degree of population structure (Fst=0.2), low gene flow (Nm=1.0) and low mutation rate (4 Nµ=0.07). Thus, the low genetic diversity is probably a result of a low mutation rate in DNA, although the gene flow (due to global movement of horses) is large enough to allow the spread of novel mutations. Surprisingly, isolates from Icelandic horses were not found to be different from other isolates, in spite of the fact that these have been isolated for thousands of years. The study indicates that the global P. equorum population is essentially homogenous, and continents do not appear to be strong barriers for the population structure of this species. Consequently, the potential spread of rare anthelmintic resistance genes may be rapid in a homogenous population.

Genetic and morphological variation in Echinorhynchus gadi Zoega in Müller, 1776 (Acanthocephala: Echinorhynchidae) from Atlantic cod Gadus morhua L.

Previous studies have shown considerable variability in morphological features and the existence of genetically distinct sibling species in the acanthocephalan Echinorhynchus gadi Zoega in Müller, 1776. The aim of the present study was to follow up and extend those earlier studies by using a combination of DNA analysis and morphometrics to investigate differences between samples of E. gadi from Atlantic cod Gadus morhua L. caught at five fishing grounds in the Baltic Sea and three in different parts of the North Atlantic. Twelve morphological features were measured in 431 specimens of E. gadi, 99 individuals were studied by polymerase chain reaction-restriction fragment length polymorphosm (PCR-RFLP), and selected PCR products were sequenced. The molecular analyses showed the nucleotide sequences of E. gadi rDNA from cod caught at all the sampling sites to be identical. The comparative morphological study, in contrast, revealed significant differences between samples of E. gadi from different sampling sites and showed the separation of E. gadi into two groups corresponding approximately to the systematic classification of cod into the two subspecies, Atlantic G. morhua morhua and Baltic G. morhua callarias. The E. gadi infrapopulation size had a significant effect on some of the morphological features. The results are discussed in relation to cod population biology, the hydrography of the study area and the history of the Baltic Sea formation.

Molecular identification and transmission studies of X-cell parasites from Atlantic cod Gadus morhua (Gadiformes: Gadidae) and the northern black flounder Pseudopleuronectes obscurus (Pleuronectiformes: Pleuronectidae).

BACKGROUND: Epidermal pseudotumours from Hippoglossoides dubius and Acanthogobius flavimanus in Japan and gill lesions in Limanda limanda from the UK have been shown to be caused by phylogenetically related protozoan parasites, known collectively as X-cells. However, the phylogenetic position of the X-cell group is not well supported within any of the existing protozoan phyla and they are currently thought to be members of the Alveolata.Ultrastructural features of X-cells in fish pseudotumours are somewhat limited and no typical environmental stages, such as spores or flagellated cells, have been observed. The life cycles for these parasites have not been demonstrated and it remains unknown how transmission to a new host occurs. In the present study, pseudobranchial pseudotumours from Atlantic cod, Gadus morhua, in Iceland and epidermal pseudotumours from the northern black flounder, Pseudopleuronectes obscurus, in Japan were used in experimental transmission studies to establish whether direct transmission of the parasite is achievable. In addition, X-cells from Atlantic cod were sequenced to confirm whether they are phylogenetically related to other X-cells and epidermal pseudotumours from the northern black flounder were analysed to establish whether the same parasite is responsible for infecting different flatfish species in Japan. RESULTS: Phylogenetic analyses of small subunit ribosomal DNA (SSU rDNA) sequence data from Atlantic cod X-cells show that they are a related parasite that occupies a basal position to the clade containing other X-cell parasites. The X-cell parasite causing epidermal pseudotumours in P. obscurus is the same parasite that causes pseudotumours in H. dubius. Direct, fish to fish, transmission of the X-cell parasites used in this study, via oral feeding or injection, was not achieved. Non-amoeboid X-cells are contained within discrete sac-like structures that are loosely attached to epidermal pseudotumours in flatfish; these X-cells are able to tolerate exposure to seawater. A sensitive nested PCR assay was developed for the sub clinical detection of both parasites and to assist in future life cycle studies. PCR revealed that the parasite in P. obscurus was detectable in non-pseudotumourous areas of fish that had pseudotumours present in other areas of the body. CONCLUSIONS: The inability to successfully transmit both parasites in this study suggests that either host detachment combined with a period of independent development or an alternate host is required to complete the life cycle for X-cell parasites. Phylogenetic analyses of SSU rDNA confirm a monophyletic grouping for all sequenced X-cell parasites, but do not robustly support their placement within any established protist phylum. Analysis of SSU rDNA from X-cells in Japanese flatfish reveals that the same parasite can infect more than one species of fish.

Pseudobranchial X-cell pseudotumors in young wild and farmed atlantic cod Gadus morhua in Iceland.

This study investigated the prevalence of pseudobranchial X-cell pseudotumors in 2 year classes of wild juvenile cod and to a lesser extent in older cod in NW Iceland. The disease was also monitored in farmed wild-caught juvenile cod. The youngest wild cod detected that had X-cell infections were 6.5 to 13.0 cm in length, with prevalence reaching a maximum level of 7%. The highest prevalence (23%) was recorded in 18.5 to 27.0 cm fish. The mean prevalence in older cod (25.0 to 76.0 cm in length) was 7% but decreased with increasing age. The mean prevalence of X-cell pseudotumors in farmed juvenile cod was < or =1% during winter rearing in land-based tanks. Higher prevalence (2 to 15%) was noted in dead and moribund fish. Diseased farmed fish were usually emaciated, and mortality due to the disease was noticeable.

Progress of co-infections of Trichodina cooperi and T. murmanica parasitising farmed Atlantic cod Gadus morhua juveniles in Iceland.

Two year classes of wild cod juveniles, caught for on-rearing in shore-based tanks, were examined for Trichodina spp. infections at regular intervals for 9 mo. The prevalence, density and proportion of each species found was determined. Additionally, biomass, seawater temperature and salinity in the tanks was recorded regularly. Two species were identified: T. cooperi and T. murmanica. Their prevalence, density and proportion varied between sampling times, T. cooperi being the dominant species, more prevalent and in higher density in the beginning. In the following months, T. murmanica gradually increased its prevalence, density and proportion, reaching an almost total dominance in both year classes after 7 mo of rearing. The results indicate that the rearing environment on this farm favoured T. murmanica. Changes in salinity could explain this to some extent; a drop in salinity, due to an inflow of geothermal freshwater to control the temperature during the coldest months, coincided fairly well with an increasing proportion of T. murmanica. Transfer of wild fish into the rearing environment, with a subsequent increase in biomass, resulted in a proliferation of trichodinids. This may have altered the interaction between species and the competition for resources. It is conceivable that a higher host density favours one Trichodina species over the other. Temperature could also play a role. During the first 3 to 4 mo of rearing, the temperature in the tanks followed the temperature of the open sea, which dropped by 3 to 5 degrees C. This study is a part of a larger project on monitoring the progress of various infectious diseases in farmed cod of wild origin.

Infestation of Werneckiella equi on Icelandic horses, characteristics of predilection sites and lice dermatitis.

Lice infestations on horses caused by the lice Werneckiella (Damalinia) equi and Haematopinus equi are observed worldwide. In this study, the distribution and clinical manifestations of lice on Icelandic horses were examined. Thirty-eight out of 93 animals (40.86%) were identified as infested with W. equi. Sixty-eight animals (73.12%) presented dermatological lesions associated with lice infestation, while only 32 of these animals presented lice. Six animals had no clinical signs although of being lice-positive, and 19 animals (20.43%) showed neither lice nor clinical manifestations. Lice burdens varied from animal to animal, and clinical manifestations occurred at all levels of infestation. Focal alopecia was the main clinical sign (83.78%) on lice-positive horses, while scaling and crusts occurred in 10.81% and 9.68% of the cases, respectively. Clinical signs present in the head and the neck/mane area were found to be an indication of lice infestation in horses.

Dermatological and parasitological evaluation of infestations with chewing lice (Werneckiella equi) on horses and treatment using imidacloprid.

Lice infestations in horses caused by the chewing louse Werneckiella (Damalinia) equi are observed worldwide. In the present study, the efficacy of 10% imidacloprid was tested on horses naturally infested with lice. Two groups of animals received a double application of 4 ml and 8 ml Advantage 10% spot-on on day 0 and 28 either. Horses, presenting dermatological signs with negative lice counts, were also included in this investigation. 40.86% of the horses presented positive lice counts and 84.21% of these animals showed clinical dermatologic signs. 65.45% of the lice-negative horses also showed clinical manifestations. Two days after treatment, lice counts dropped in both the treatment groups and on day 56, all animals were free of alive lice, and dermatological lesions decreased significantly (P<0.001) in both the lice-positive and the negative animals. No correlation (P>0.050) between lice burden and clinical signs was detected.

Natural infestation of the chewing lice (Werneckiella equi) on horses and treatment with imidacloprid and phoxim.

Infestation with the chewing louse (Werneckiella (Damalinia) equi) can be found on horses world-wide. Louse infestations, including clinical signs of louse-derived dermatitis, are known from Icelandic horses. A clinical field investigation was conducted in Iceland using horses with natural louse infestations to evaluate the efficacy of imidacloprid in a 10% solution in comparison with phoxim in a 0.05% solution. A total of 27 horses received a single imidacloprid treatment using 16 ml of the 10% solution along the mane and on the dorso-lateral trunk. A further 43 horses were treated twice, 14 days apart, with phoxim, using 2 x 50 ml solution applied along the mane and the dorso-lateral trunk. At the final evaluation on day 28, complete control of the lice was obtained for the imidacloprid treated horses and only a single moribund louse was found on two horses treated with phoxim.

Parasites of the arctic fox (Alopex lagopus) in Iceland.

Forty-four of 50 arctic foxes (Alopex lagopus) in Iceland harbored 15 species of intestinal parasites, including Protozoa: Eimeria sp. or Isospora sp. (in 4%); Trematoda: Cryptocotyle lingua (24%), Plagiorchis elegans (4%), Brachylaemus sp. (12%), Tristriata sp. (10%), and Spelotrema sp. (8%); Cestoda: Mesocestoides canislagopodis (72%), Schistocephalus solidus (2%), and Diphyllobothrium dendriticum (4%); Nematoda: Toxascaris leonina (50%), Toxocara canis (2%), Uncinaria stenocephala (4%), and eggs of the lung worm Capillaria aerophila (6%); and Acanthocephala: Polymorphus meyeri (8%) and Corynosoma hadweni (2%). Only four of the species previously had been recorded in Iceland. Eleven species are new records in Iceland and six appear to be new host records. Two additional nematodes, Stegophorus stercorarii and Syphacia sp., probably were ingested accidentally with the prey. Foxes from coastal habitats harbored 14 parasitic species while only five species were found in foxes from inland habitats. Arctic foxes from coastal habitats generally had higher helminth burdens and harbored more parasitic species per fox than foxes from inland habitats.