Identification of a new gregarine parasite associated with mass mortality events of freshwater pearl mussels (Margaritifera margaritifera) in Sweden.

Freshwater bivalves play key ecological roles in lakes and rivers, largely contributing to healthy ecosystems. The freshwater pearl mussel, Margaritifera margaritifera, is found in Europe and on the East coast of North America. Once common in oxygenated streams, M. margaritifera is rapidly declining and consequently assessed as a threatened species worldwide. Deterioration of water quality has been considered the main factor for the mass mortality events affecting this species. Yet, the role of parasitic infections has not been investigated. Here, we report the discovery of three novel protist lineages found in Swedish populations of M. margaritifera belonging to one of the terrestrial groups of gregarines (Eugregarinorida, Apicomplexa). These lineages are closely related-but clearly separated-from the tadpole parasite Nematopsis temporariae. In one lineage, which is specifically associated with mortality events of M. margaritifera, we found cysts containing single vermiform zoites in the gills and other organs of diseased individuals using microscopy and in situ hybridization. This represents the first report of a parasitic infection in M. margaritifera that may be linked to the decline of this mussel species. We propose a tentative life cycle with the distribution of different developmental stages and potential exit from the host into the environment.

An apicomplexan parasite drives the collapse of the bay scallop population in New York.

The bay scallop, Argopecten irradians, represents a commercially, culturally and ecologically important species found along the United States' Atlantic and Gulf coasts. Since 2019, scallop populations in New York have been suffering large-scale summer mortalities resulting in 90-99% reduction in biomass of adult scallops. Preliminary investigations of these mortality events showed 100% prevalence of an apicomplexan parasite infecting kidney tissues. This study was designed to provide histological, ultrastructural and molecular characteristics of a non-described parasite, member of the newly established Marosporida clade (Apicomplexa) and provisionally named BSM (Bay Scallop Marosporida). Molecular diagnostics tools (quantitative PCR, in situ hybridization) were developed and used to monitor disease development. Results showed that BSM disrupts multiple scallop tissues including kidney, adductor muscle, gill, and gonad. Microscopy observations allowed the identification of both intracellular and extracellular stages of the parasite. Field surveys demonstrated a strong seasonal signature in disease prevalence and intensity, as severe cases and mortality increase as summer progresses. These results strongly suggest that BSM infection plays a major role in the collapse of bay scallop populations in New York. In this framework, BSM may synergistically interact with stressful environmental conditions to impair the host and lead to mortality.

Tetracapsuloides bryosalmonae and proliferative kidney disease in Icelandic salmonids - Comparative data from two different time periods.

Tetracapsuloides bryosalmonae is a myxozoan parasite and the causative agent of proliferative kidney disease (PKD), a serious, temperature-dependent and emerging disease affecting salmonid fish. It was first identified in Iceland in 2008, from Arctic charr inhabiting a shallow lowland lake. The aim of this study was to investigate the distribution and prevalence of macroscopic and subclinical T. bryosalmonae infections in Icelandic salmonids and compare different time periods, in context with depths, volumes, altitudes and areas of the lakes and fish age. Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) from 34 lakes, sampled between 1994-1998 and 2009-2017, were examined for macroscopic signs of PKD (n = 2,151) and the presence of T. bryosalmonae infections (n = 1,424). In the earlier period, 43% of lakes (10/23) harboured T. bryosalmonae -infected fish. The mean prevalence in those lakes was 62.1%, being most common in shallow lowland lakes whilst deeper lakes at high altitudes were all free from infection. Only a single fish from one lake showed macroscopic signs of PKD, a shallow lowland lake in southwestern Iceland. In the latter period, T. bryosalmonae was found in 16/18 lakes studied (89%), with a mean prevalence of 78-79% (excluding T.b. free lakes), being most common in the smaller, shallower lakes at lower alttudes. Macroscopic signs of PKD were observed in 11 of 18 of the lakes studied (61%) with prevalences up to 67%, most common in younger fish inhabiting small shallow lowland lakes. The results indicate that the distribution of T. bryosalmonae and the presence of PKD in Iceland have increased over the last few decades. The disease was almost non-existent in the 1990s but has become very common during the last decade or two. With further water temperature increases, as predicted by climate models, PKD is likely to increasingly affect wild salmonid populations in Iceland.

A phylogenetically unresolved apicomplexan (APXSc) causing swirl lesions in the Tehuelche scallop, Aequipecten tehuelchus, from the Southwest Atlantic coast.

The study reports a previously unknown apicomplexan (APXSc) parasite infecting wild scallops Aequipecten tehuelchus (d'Orbigny, 1842) from two separate areas (La Tapera and Punta Conos) of the San José gulf, in Patagonia Argentina. Histology, transmission electron microscope, molecular analyses and in situ hybridization were performed to describe the morphology of APXSc, and confirm its phylogenetic status. The prevalence of APXSc infection was 24% and 72% in scallops from La Tapera and Punta Conos, respectively. Seasonal variation was observed for scallops from La Tapera, recording highest prevalence in summer. A positive relationship between the presence of the APXSc and the size of the scallops was observed. A SSU rDNA consensus sequence of 1758 base pairs was generated which has a 94.8% identity to sequences obtained from a pathogenic apicomplexan parasite infecting Ostrea chilensis in New Zealand, but not closely related to other apicomplexans. The asexual reproduction, i.e. merogony, occurs in the Tehuelche scallop whilst the gamogonic and sporogonic stages were absent, suggesting a yet unknown definitive host. Severe host inflammation response involving fibroblast-like hemocytes surrounding the APXSc in the form of granuloma-like "swirls" is characteristic for this apicomplexan infection. Further studies are needed to reveal the life cycle, and presumable pathogenicity of APXSc.

A case report and statewide surveillance of "weak meat" condition of Alaska weathervane scallops, Patinopecten caurinus, linked to a recently identified pathogenic parasite, Merocystis kathae (Apicomplexa: Aggregatidae).

Weathervane scallop, Patinopecten caurinus, the largest scallop species in the world, is distributed from northern California, U.S.A., to the Bering Sea, and is only commercially harvested in Alaska. The fishery is considered well managed by the State of Alaska (U.S.A) Department of Fish and Game (ADF&G) and federal government, with many precautionary measures in place to avoid overharvest. There have been episodic declines in some management areas due to unknown causes. Fishermen also encounter scallops with abnormal adductor muscles, a condition colloquially termed "weak meat", characterized by the retention of muscle when shucked, an obvious darkened discoloration, and/or an abnormal texture making the product unacceptable for marketing. A similar syndrome in Atlantic sea scallops, Placopecten magellanicus, described as "gray meat", occurs in the eastern U.S. and Canada, and proposed causes include senescence, loss of bioenergetics due to chronic infestations, or a synergism of these factors. Recently a severe apicomplexan infection was found to cause a gray meat condition in Iceland scallops, Chlamys islandica, and the collapse of that stock. This parasite was subsequently detected in Atlantic sea scallops with the gray meat condition off the U.S. East Coast. Studies that followed identified the parasite as Merocystis kathae, previously described from the common whelk, Buccinum undatum, more than 100 years ago. In 2015 Bering Sea fishermen reported weak meat in their catch, so samples were submitted to ADF&G for diagnosis. Adductor muscles from all affected scallops had many large foci of an apicomplexan associated with necrosis, fibrosis, and muscular atrophy. Given the reduced quality, marketability, and possibly fitness of affected scallops, we performed a survey to estimate prevalence, intensity, and geographic distribution of this apicomplexan in Alaskan weathervane scallops. We sampled 180 scallops, from individual beds within each of the three major geographically broad scallop areas in Alaska. Overall prevalence was about 82%, ranging from 69 to 100% by district. Overall mean infection intensity, based on the number of parasite foci/section, was about 9 (range of 5-29, by location), with scallops from the Bering Sea and Southwest Kodiak being most severely infected. Molecular analyses confirmed that the Alaskan parasite is M. kathae, i.e., the same apicomplexan that caused the collapse of Icelandic scallops and a suspected cause for gray meat and mass mortality of Atlantic sea scallops in northeast North America.

The presence of sporogonic stages of Tetracapsuloides bryosalmonae in Icelandic salmonids detected using in situ hybridisation.

Proliferative kidney disease (PKD) is a widespread temperature-dependent disease in salmonids caused by the myxozoan parasite, Tetracapsuloides bryosalmonae (Canning, Curry, Feist, Longshaw et Okamura, 1999) (Tb). Tb has a two-host life cycle, involving fish as an intermediate host and freshwater bryozoans as the definitive host. Although salmonids are acknowledged as hosts for the parasite, it is less clear which fish species are active hosts in the life cycle of Tb. Differences in infection dynamics have been observed between some fish species, which are thought to be related to the existence of two main Tb-strains, the American and European. Iceland, having three species of indigenous salmonids and positioned geographically between Europe and North America, is an ideal location to study the natural development of Tb in wild fish. The main aim of this study was to determine the genetic origin of Tb in Iceland and confirm whether mature spores are produced in Icelandic salmonids. In this study, Icelandic salmonids were infected with the European Tb-strain. In situ hybridisation revealed that intraluminal sporogonic stages, including mature spores, were commonly observed in all three salmonid species. The presence of intraluminal stages has previously been confirmed in brown trout Salmo trutta Linnaeus and Atlantic salmon S. salar Linnaeus in Europe, but they have only been observed in Arctic charr Salvelinus alpinus (Linnaeus) in North America, infected by the local strain. This is, therefore, the first time that sporogonic stages have been observed in Arctic charr in Europe, where fish are infected with the European Tb-strain. Our data strongly suggest that all the three salmonid species inhabiting Icelandic waters serve as active hosts in the life cycle of Tb. However, for full confirmation, transmission trials are needed.

Peptidylarginine Deiminase (PAD) and Post-Translational Protein Deimination-Novel Insights into Alveolata Metabolism, Epigenetic Regulation and Host-Pathogen Interactions.

The alveolates (Superphylum Alveolata) comprise a group of primarily single-celled eukaryotes that have adopted extremely diverse modes of nutrition, such as predation, photoautotrophy and parasitism. The alveolates consists of several major phyla including the apicomplexans, a large group of unicellular, spore forming obligate intracellular parasites, and chromerids, which are believed to be the phototrophic ancestors of the parasitic apicomplexans. Molecular pathways involved in Alveolata host-pathogen interactions, epigenetic regulation and metabolism in parasite development remain to be fully understood. Peptidylarginine deiminases (PADs) are a phylogenetically conserved enzyme family which causes post-translational protein deimination, affecting protein function through the conversion of arginine to citrulline in a wide range of target proteins, contributing to protein moonlighting in physiological and pathological processes. The identification of deiminated protein targets in alveolate parasites may therefore provide novel insight into pathogen survival and host-pathogen interactions. The current study assessed PAD homologues and deiminated protein profiles of two alveolate parasites, Piridium sociabile (Chromerida) and Merocystis kathae (Apicomplexa). Histological analysis verified strong cytoplasmic PAD expression in both Alveolates, detected deiminated proteins in nuclear and cytoplasmic compartments of the alveolate parasites and verified the presence of citrullinated histone H3 in Alveolata nucleus, indicating roles in epigenetic regulation. Histone H3 citrullination was also found significantly elevated in the host tissue, indicative of neutrophil extracellular trap formation, a host-defence mechanism against a range of pathogens, particularly those that are too large for phagocytosis. Proteomic analysis of deiminated proteins from both Alveolata identified GO and KEGG pathways strongly relating to metabolic and genetic regulation, with some species-specific differences between the apicomplexan and the chromerid. Our findings provide novel insights into roles for the conserved PAD/ADI enzyme family in the regulation of metabolic and epigenetic pathways in alveolate parasites, possibly also relating to their life cycle and host-pathogen interactions.

Phylogenomics Identifies a New Major Subgroup of Apicomplexans, Marosporida class nov., with Extreme Apicoplast Genome Reduction.

The phylum Apicomplexa consists largely of obligate animal parasites that include the causative agents of human diseases such as malaria. Apicomplexans have also emerged as models to study the evolution of nonphotosynthetic plastids, as they contain a relict chloroplast known as the apicoplast. The apicoplast offers important clues into how apicomplexan parasites evolved from free-living ancestors and can provide insights into reductive organelle evolution. Here, we sequenced the transcriptomes and apicoplast genomes of three deep-branching apicomplexans, Margolisiella islandica, Aggregata octopiana, and Merocystis kathae. Phylogenomic analyses show that these taxa, together with Rhytidocystis, form a new lineage of apicomplexans that is sister to the Coccidia and Hematozoa (the lineages including most medically significant taxa). Members of this clade retain plastid genomes and the canonical apicomplexan plastid metabolism. However, the apicoplast genomes of Margolisiella and Rhytidocystis are the most reduced of any apicoplast, are extremely GC-poor, and have even lost genes for the canonical plastidial RNA polymerase. This new lineage of apicomplexans, for which we propose the class Marosporida class nov., occupies a key intermediate position in the apicomplexan phylogeny, and adds a new complexity to the models of stepwise reductive evolution of genome structure and organelle function in these parasites.

A novel histozoic myxosporean, Enteromyxum caesio n. sp., infecting the redbelly yellowtail fusilier, Caesio cuning, with the creation of the Enteromyxidae n. fam., to formally accommodate this commercially important genus.

Gastrointestinal myxosporean parasites from the genus Enteromyxum are known to cause severe disease, resulting in high mortalities in numerous species of cultured marine fishes globally. Originally described as Myxidium spp., they were transferred to a new genus, Enteromyxum, to emphasize their novel characteristics. Their retention in the family Myxidiidae at the time was warranted, but more comprehensive phylogenetic analyses have since demonstrated the need for a new family for these parasites. We discovered a novel Enteromyxum in wild fish from Malaysia and herein describe the fourth species in the genus and erect a new family, the Enteromyxidae n. fam., to accommodate them. Enteromyxum caesio n. sp. is described infecting the tissues of the stomach in the redbelly yellowtail fusilier, Caesio cuning, from Malaysia. The new species is distinct from all others in the genus, as the myxospores although morphologically similar, are significantly smaller in size. Furthermore, small subunit ribosomal DNA sequence data reveal that E. caesio is <84% similar to others in the genus, but collectively they form a robust and discrete clade, the Enteromyxidae n. fam., which is placed as a sister taxon to other histozoic marine myxosporeans. In addition, we describe, using transmission electron microscopy, the epicellular stages of Enteromyxum fugu and show a scanning electron micrograph of a mature myxospore of E. caesio detailing the otherwise indistinct sutural line, features of the polar capsules and spore valve ridges. The Enteromyxidae n. fam. is a commercially important group of parasites infecting the gastrointestinal tract of marine fishes and the histozoic species can cause the disease enteromyxosis in intensive finfish aquaculture facilities. Epicellular and sloughed histozoic stages are responsible for fish-to-fish transmission in net pen aquaculture systems but actinospores from an annelid host are thought to be necessary for transmission to fish in the wild.

Multiple Independent Origins of Apicomplexan-Like Parasites.

The apicomplexans are a group of obligate animal pathogens that include Plasmodium (malaria), Toxoplasma (toxoplasmosis), and Cryptosporidium (cryptosporidiosis) [1]. They are an extremely diverse and specious group but are nevertheless united by a distinctive suite of cytoskeletal and secretory structures related to infection, called the apical complex, which is used to recognize and gain entry into animal host cells. The apicomplexans are also known to have evolved from free-living photosynthetic ancestors and retain a relict plastid (the apicoplast), which is non-photosynthetic but houses a number of other essential metabolic pathways [2]. Their closest relatives include a mix of both photosynthetic algae (chromerids) and non-photosynthetic microbial predators (colpodellids) [3]. Genomic analyses of these free-living relatives have revealed a great deal about how the alga-parasite transition may have taken place, as well as origins of parasitism more generally [4]. Here, we show that, despite the surprisingly complex origin of apicomplexans from algae, this transition actually occurred at least three times independently. Using single-cell genomics and transcriptomics from diverse uncultivated parasites, we find that two genera previously classified within the Apicomplexa, Piridium and Platyproteum, form separately branching lineages in phylogenomic analyses. Both retain cryptic plastids with genomic and metabolic features convergent with apicomplexans. These findings suggest a predilection in this lineage for both the convergent loss of photosynthesis and transition to parasitism, resulting in multiple lineages of superficially similar animal parasites.

Outbreak of viral haemorrhagic septicaemia (VHS) in lumpfish (Cyclopterus lumpus) in Iceland caused by VHS virus genotype IV.

A novel viral haemorrhagic septicaemia virus (VHSV) of genotype IV was isolated from wild lumpfish (Cyclopterus lumpus), brought to a land-based farm in Iceland, to serve as broodfish. Two groups of lumpfish juveniles, kept in tanks in the same facility, got infected. The virus isolated was identified as VHSV by ELISA and real-time RT-PCR. Phylogenetic analysis, based on the glycoprotein (G) gene sequences, may indicate a novel subgroup of VHSV genotype IV. In controlled laboratory exposure studies with this new isolate, there was 3% survival in the I.P. injection challenged group while there was 90% survival in the immersion group. VHSV was not re-isolated from fish challenged by immersion. In a cohabitation trial, lumpfish infected I.P. (shedders) were placed in tanks with naïve lumpfish as well as naïve Atlantic salmon (Salmo salar L.). 10% of the lumpfish shedders and 43%-50% of the cohabiting lumpfish survived after 4 weeks. 80%-92% of the Atlantic salmon survived, but no viral RNA was detected by real-time RT-PCR nor VHSV was isolated from Atlantic salmon. This is the first isolation of a notifiable virus in Iceland and the first report of VHSV of genotype IV in European waters.

Studies of Myxidium giardi Cépède, 1906 infections in Icelandic eels identifies a genetically diverse clade of myxosporeans that represents the Paramyxidium n. g. (Myxosporea: Myxidiidae).

BACKGROUND: The myxosporean Myxidium giardi Cépède, 1906 was described infecting the kidney of the European eel, Anguilla anguilla (L.), having spindle-shaped myxospores and terminal sub-spherical polar capsules. Since then, numerous anguillid eels globally have been documented to have similar Myxidium infections. Many of these have been identified using the morphological features of myxospores or by the location of infection in the host, and some have been subsequently synonymised with M. giardi. Therefore, it is not clear whether M. giardi is a widely distributed parasite, infecting numerous species of eels, in multiple organs, or whether some infections represent other, morphologically similar but different species of myxosporeans. The aim of the present study was to assess the status of M. giardi infections in Icelandic eels, and related fish hosts in Malaysia and to use spore morphology and molecular techniques to evaluate the diversity of myxosporeans present. RESULTS: The morphologies of the myxospores from Icelandic eels were very similar but the overall dimensions were significantly different from the various tissue locations. Myxospores from the kidney of the Malaysian tarpon, Megalops cyprinoides (Broussonet), were noticeably smaller. However, the SSU rDNA sequences from the different tissues locations in eels, were all very distinct, with percentage similarities ranging from 92.93% to as low as 89.8%, with the sequence from Malaysia being even more dissimilar. Molecular phylogenies consistently placed these sequences together in a clade that we refer to as the Paramyxidium clade that is strongly associated with the Myxidium clade (sensu stricto). We erect the genus Paramyxidium n. g. (Myxidiidae) to accommodate these histozoic taxa, and transfer Myxidium giardi as Paramyxidium giardi Cépède, 1906 n. comb. as the type-species. CONCLUSIONS: There is not a single species of Myxidium (M. giardi) causing systemic infections in eels in Iceland. There are three species, confirmed with a robust phylogeny, one of which represents Paramyxidium giardi n. comb. Additional species probably exist that infect different tissues in the eel and the site of infection in the host fish is an important diagnostic feature for this group (Paramyxidium n. g. clade). Myxospore morphology is generally conserved in the Paramyxidium clade, although actual spore dimensions can vary between some species. Paramyxidium spp. are currently only known to infect fishes from the Elopomorpha.

Digestive gland inclusion bodies in queen conch (Lobatus gigas) are non-parasitic.

Unusual inclusion bodies occur within the epithelial cells of the digestive gland of queen conch, Lobatus gigas, and have previously been described as apicomplexan parasites. The aim of this study was to investigate the parasitic features of these inclusion bodies in queen conch. L. gigas from St. Kitts (Caribbean Sea) consistently (100% of n = 61) showed large numbers of ovoid to tri-bulbous dark brown inclusion bodies (15 × 30 µm) within vacuolar cells. Histochemical stains demonstrated iron, melanin, and glycoprotein and/or mucopolysaccharide within the inclusion bodies. Microscopic features indicative of a host response to injury were lacking in every case, as were consistent morphological forms to indicate distinct parasitic stages. Transmission electron microscopy failed to reveal cellular organelles of parasitic organisms and DNA extractions of purified inclusion bodies did not yield sufficient concentrations for successful PCR amplification. Scanning electron microscopy with energy dispersive X-ray analysis revealed a number of elements, particularly iron, within the inclusion bodies. We conclude that the inclusion bodies are not an infectious agent, and hypothesize that they represent a storage form for iron, and potentially other elements, within a protein matrix. Similar structures have been described in the digestive glands of other invertebrates, including prosobranchs.

Harmless sea snail parasite causes mass mortalities in numerous commercial scallop populations in the northern hemisphere.

Apicomplexans comprise a group of unicellular, often highly pathogenic, obligate parasites exploiting either one or two hosts to complete a full reproductive cycle. For decades, various scallop populations have suffered cyclical mass mortality events, several of which shown to be caused by apicomplexan infections. We report the first dual mollusc life cycle for an apicomplexan: a species highly pathogenic in various pectinid bivalve species, but apathogenic when infecting the common whelk as Merocystis kathae. The sympatric distribution of the common whelk and scallops in the North Atlantic makes transmission extremely effective, occurring via the gastrointestinal tract, by scavenging and predation in whelks and unselective filter feeding in scallops. Infective sporozoites from whelks utilize scallops´ haemocytes to reach muscular tissue, where asexual reproduction occurs. Phylogenetically, this apicomplexan is robustly placed within the Aggregatidae and its inclusion in analyses supports a common ancestry with other basal invertebrate apicomplexans. Scallops seem able to regulate low-level infections of M. kathae as they exist in normal populations while epizootics occur during high levels of exposure from locally infected whelks. A targeted removal of whelks from valuable scallop grounds would be advantageous to minimize the occurrence of M. kathae epizootics and prevent damaging economic losses.

X-Cells Are Globally Distributed, Genetically Divergent Fish Parasites Related to Perkinsids and Dinoflagellates.

"X-cells" have long been associated with tumor-like formations (xenomas) in marine fish, including many of commercial interest. The name was first used to refer to the large polygonal cells that were found in epidermal xenomas from flatfish from the Pacific Northwest [1]. Similar looking cells from pseudobranchial xenomas had previously been reported from cod in the Atlantic [2] and Pacific Oceans [3]. X-cell pathologies have been reported from five teleost orders: Pleuronectiformes (flatfish), Perciformes (perch-like fish), Gadiformes (cods), Siluriformes (catfish), and Salmoniformes (salmonids). Various explanations have been elicited for their etiology, including being adenomas or adenocarcinomas [4, 5], virally transformed fish cells [6-8], or products of coastal pollution [9, 10]. It was hypothesized that X-cells were protozoan parasites [1, 11-13], and although recent molecular analyses have confirmed this, they have failed to place them in any phylum [14-18], demonstrating weak phylogenetic associations with the haplosporidians [16] or the alveolates [15]. Here, we sequenced rRNA genes from European and Japanese fish that are known to develop X-cell xenomas. We also generated a metagenomic sequence library from X-cell xenomas of blue whiting and Atlantic cod and assembled 63 X-cell protein-coding genes for a eukaryote-wide phylogenomic analysis. We show that X-cells group in two highly divergent clades, robustly sister to the bivalve parasite Perkinsus. We formally describe these as Gadixcellia and Xcellia and provide a phylogenetic context to catalyze future research. We also screened Atlantic cod populations for xenomas and residual pathologies and show that X-cell infections are more prevalent and widespread than previously known.

Redescription and phylogenetic position of Myxobolus aeglefini and Myxobolus platessae n. comb. (Myxosporea), parasites in the cartilage of some North Atlantic marine fishes, with notes on the phylogeny and classification of the Platysporina.

Myxobolus 'aeglefini' Auerbach, 1906 was originally described from cranial cartilage of North sea haddock (Melanogrammus aeglefinus), but has subsequently been recorded from cartilaginous tissues of a range of other gadoid hosts, from pleuronectids and from lumpsucker (Cyclopterus lumpus) in the North Atlantic and from a zoarcid fish in the Japan Sea (Pacific). We obtained partial small-subunit rDNA sequences of Myxobolus 'aeglefini' from gadoids and pleuronectids from Norway and Iceland. The sequences from gadoids and pleuronectids represented two different genotypes, showing 98.2% identity. Morphometric studies on the spores from selected gadids and pleuronectids revealed slight but statistically significant differences in spore dimensions associated with the genotypes, the spores from pleuronectids were thicker and with larger polar capsules. We identify the morpho- and genotype from gadoids with Myxobolus 'aeglefini' sensu Auerbach, and the one from pleuronectids with Sphaerospora platessae Woodcock, 1904 as Myxobolus platessae n. comb. The latter species was originally described from Irish Sea plaice (Pleuronectes platessa). Myxobolus albi Picon et al., 2009 described from the common goby Pomatoschistus microps in Scotland is a synonym of M. 'aeglefini'. The Pacific Myxobolus 'aeglefini' represents a separate species, showing only 97.4-97.6% identity to the Atlantic species. In phylogenetic analyses based on SSU rDNA sequences, these and some related marine chondrotropic Myxobolus spp. form a distinct well supported group. This clusters with freshwater and marine myxobolids and Triangula and Cardimyxobolus species, in a basal clade in the phylogeny of the Platysporina. Members of family Myxobilatidae, Ortholinea spp. (currently Ortholineidae) and sequences of some other urinary system infecting myxosporeans form a well supported clade among members of the suborder Platysporina. Based on phylogenetic analyses, we propose the following changes to the classification of Myxosporea: i) Ortholineidae is dismantled and Ortholinea spp. transferred to Myxobilatidae, and ii) Myxobilatidae is transferred from suborder Variisporina to Platysporina.

Gray meat in the Atlantic sea scallop, Placopecten magellanicus, and the identification of a known pathogenic scallop apicomplexan.

Atlantic sea scallop (Placopecten magellanicus) meats are normally firm and creamy white. However, scallops with small, darkened and stringy adductor muscle (gray meat) episodically occur along the Eastern Seaboard, most recently in the rotational management areas of Georges Bank after extended fishing closures. These gray meat scallops are associated with reduced harvestable biomass and mass mortality events. We tested age, nutritional stress and disease as causative agents for this condition. Adult scallops of different shell heights (SH) ranging from (90-145mm) were collected from Georges Bank and analyzed for meat quality and the presence of pathogens using biochemical, histopathological and molecular methods. Gray meat occurrence was weakly correlated with shell height only explaining 8.49% of the variance in a generalized additive model (GAMS). Gray meat weights were lower than white meat (p<0.001) and there was a dramatic reduction in protein content (p<0.05) in gray meat scallops associated with extensive myodegeneration. Amino acid profiles confirmed the breakdown of muscle tissue with an increase in free hydroxyproline in gray meat scallops. Infection by an apicomplexan parasite was detected in the muscle tissue of all gray meat scallops tested. An intermediate pathology stage (brown meat) was also identified. As the parasitic infection increased, meat quality decreased. Numerous developmental stages of the parasite were present in various organs of the scallops. This apicomplexan has an identical SSU rDNA sequence to a novel parasite occurring in the Iceland scallop during a recent mass mortality event. The range of this parasite in Atlantic sea scallops and the effect of abiotic/biotic stressors on pathogenicity are currently unknown. Results from this study link an apicomplexan species, known to be highly pathogenic in scallops, to gray meat occurrence with a potentially high impact on the fishery.

[Demodex folliculorum a hidden cause of blepharitis].

UNLABELLED: Meibomian gland dysfunction (MGD) is a common cause of dry eye disease. Demodex mites can cause MGD with symptoms like itching, dryness and general ocular discomfort. It is important to consider infestation with Demodex mites in individuals who are non responsive to traditional MGD treatment but also equally important when cylindrical dandruff is seen at the base of the eye lashes.. We report two individuals who had not responded to ocular and systemic treatment for MGD and were then diagnosed with Demodex mites. Treatment with BlephEx and Tea tree oil was successful. This is the first report on Demodex folliculorum in Iceland where a genetic analysis was done. KEY WORDS: Demodex, blepharitis, debris, tea tree oil, dry eye. Correspondence: Sigurlaug Guðrún Gunnarsdóttir sigurlaug@sjonlag.is.

Is an Apicomplexan Parasite Responsible for the Collapse of the Iceland Scallop (Chlamys islandica) Stock?

Due to the total and unexpected collapse of the Iceland scallop, Chlamys islandica, stocks around Iceland during the 2000s, a commercial fishing ban has been imposed on this valuable resource since 2003. Following the initial identification of an apicomplexan parasite in the scallops, a long-term surveillance program was established to evaluate the effect of the parasite on the population. The infections were highly prevalent in all shell sizes throughout the study. However, the parasite only impacts mature scallops where they cause severe macroscopic changes, characterized by an extensively diminished and abnormally coloured adductor muscle. A highly significant relationship was observed between infection intensity and gonad and adductor muscle indices. The first four years of the study, were characterized by high infection intensity and very poor condition of the adductor muscle and gonads, whilst during subsequent years, infections gradually decreased and the condition of the scallops improved. Histopathological changes were restricted to the presence of apicomplexan zoites which were widely distributed, causing varying degrees of pathology in all organs. In heavy infections, muscular and connective tissues were totally necrotized, destroying significant parts of numerous organs, especially the adductor muscle, digestive gland and gonads. The progression of the disease was in good synchrony with the mortality rates and the subsequent decline observed in the scallop stock and recruitment indices. Our findings strongly suggest that the apicomplexan parasite played a major role in the collapse of the Iceland scallop stock in Breidafjordur. In addition to causing mortality, the infections significantly impact gonad development which contributes further to the collapse of the stock in the form of lower larval recruitment. Furthermore, compelling evidence exists that this apicomplexan pathogen is causing serious disease outbreaks in other scallop populations. Similar abnormal adductor muscles and the parasite itself have been identified or observed in association with other mass mortality events in several different scallop species and commercial stocks in the northern hemisphere.

Histozoic myxosporeans infecting the stomach wall of elopiform fishes represent a novel lineage, the Gastromyxidae.

BACKGROUND: Traditional studies on myxosporeans have used myxospore morphology as the main criterion for identification and taxonomic classification, and it remains important as the fundamental diagnostic feature used to confirm myxosporean infections in fish and other vertebrate taxa. However, its use as the primary feature in systematics has led to numerous genera becoming polyphyletic in subsequent molecular phylogenetic analyses. It is now known that other features, such as the site and type of infection, can offer a higher degree of congruence with molecular data, albeit with its own inconsistencies, than basic myxospore morphology can reliably provide. METHODS: Histozoic gastrointestinal myxosporeans from two elopiform fish from Malaysia, the Pacific tarpon Megalops cyprinoides and the ten pounder Elops machnata were identified and described using morphological, histological and molecular methodologies. RESULTS: The myxospore morphology of both species corresponds to the generally accepted Myxidium morphotype, but both had a single nucleus in the sporoplasm and lacked valvular striations. In phylogenetic analyses they were robustly grouped in a discrete clade basal to myxosporeans, with similar shaped myxospores, described from gill monogeneans, which are located at the base of the multivalvulid clade. New genera Gastromyxum and Monomyxum are erected to accommodate these myxosporean taxa from fish and gill monogeneans respectively. Each are placed in a new family, the Gastromyxidae with Gastromyxum as the type genus and Monomyxidae with Monomyxum as the type genus. CONCLUSIONS: To improve modern systematics of the myxosporeans it is clear that a combination of biological, ecological, morphological and molecular data should be used in descriptive studies, and the naming and redistribution of taxa and genera is going to be necessary to achieve this. Here we demonstrate why some Myxidium-shaped myxospores should not be included in the family Myxidiidae, and create two new families to accommodate them based on their site of infection, host biology / ecology, DNA sequence data and morphological observations. Subsequent descriptive works need to follow a similar course if we are going to create a prevailing and workable systematic structure for the Myxosporea.