Recent advances in our knowledge of the Myxozoa

In the last few years two factors have helped to significantly advance our understanding of the Myxozoa. First, the phenomenal increase in fin fish aquaculture in the 1990s has lead to the increased importance of these parasites; in turn this has lead to intensified research efforts, which have increased knowledge of the development, diagnosis. and pathogenesis of myxozoans. The hallmark discovery in the 1980s that the life cycle of Myxobolus cerebralis requires development of an actinosporean stage in the oligochaete. Tubifex tubifex, led to the elucidation of the life cycles of several other myxozoans. Also, the life cycle and taxonomy of the enigmatic PKX myxozoan has been resolved: it is the alternate stage of the unusual myxozoan, Tetracapsula bryosalmonae, from bryozoans. The 18S rDNA gene of many species has been sequenced, and here we add 22 new sequences to the data set. Phylogenetic analyses using all these sequences indicate that: 1) the Myxozoa are closely related to Cnidaria (also supported by morphological data); 2) marine taxa at the genus level branch separately from genera that usually infect freshwater fishes; 3) taxa cluster more by development and tissue location than by spore morphology; 4) the tetracapsulids branched off early in myxozoan evolution, perhaps reflected by their having bryozoan, rather than annelid hosts; 5) the morphology of actinosporeans offers little information for determining their myxosporean counterparts (assuming that they exist); and 6) the marine actinosporeans from Australia appear to form a clade within the platysporinid myxosporeans. Ribosomal DNA sequences have also enabled development of diagnostic tests for myxozoans. PCR and in situ hybridisation tests based on rDNA sequences have been developed for Myxobolus cerebralis, Ceratomyxa shasta, Kudoa spp., and Tetracapsula bryosalmonae (PKX). Lectin-based and antibody tests have also been developed for certain myxozoans, such as PKX and C. shasta. We also review important diseases caused by myxozoans, which are emerging or re-emerging. Epizootics of whirling disease in wild rainbow trout (Oncorhynchus mykiss) have recently been reported throughout the Rocky Mountain states of the USA. With a dramatic increase in aquaculture of fishes using marine netpens, several marine myxozoans have been recognized or elevated in status as pathological agents. Kudoa thyrsites infections have caused severe post-harvest myoliquefaction in pen-reared Atlantic salmon (Salmo salar), and Ceratomyxa spp., Sphaerospora spp., and Myxidium leei cause disease in pen-reared sea bass (Dicentrarchus labrax) and sea bream species (family Sparidae) in Mediterranean countries.

Infectious diseases affect marine fisheries and aquaculture economics

Seafood is a growing part of the economy, but its economic value is diminished by marine diseases. Infectious diseases are common in the ocean, and here we tabulate 67 examples that can reduce commercial species' growth and survivorship or decrease seafood quality. These impacts seem most problematic in the stressful and crowded conditions of aquaculture, which increasingly dominates seafood production as wild fishery production plateaus. For instance, marine diseases of farmed oysters, shrimp, abalone, and various fishes, particularly Atlantic salmon, cost billions of dollars each year. In comparison, it is often difficult to accurately estimate disease impacts on wild populations, especially those of pelagic and subtidal species. Farmed species often receive infectious diseases from wild species and can, in turn, export infectious agents to wild species. However, the impact of disease export on wild fisheries is controversial because there are few quantitative data demonstrating that wild species near farms suffer more from infectious diseases than those in other areas. The movement of exotic infectious agents to new areas continues to be the greatest concern.

American Society for Enhanced Recovery and Perioperative Quality Initiative Joint Consensus Statement on Nutrition Screening and Therapy Within a Surgical Enhanced Recovery Pathway

Perioperative malnutrition has proven to be challenging to define, diagnose, and treat. Despite these challenges, it is well known that suboptimal nutritional status is a strong independent predictor of poor postoperative outcomes. Although perioperative caregivers consistently express recognition of the importance of nutrition screening and optimization in the perioperative period, implementation of evidence-based perioperative nutrition guidelines and pathways in the United States has been quite limited and needs to be addressed in surgery-focused recommendations. The second Perioperative Quality Initiative brought together a group of international experts with the objective of providing consensus recommendations on this important topic with the goal of (1) developing guidelines for screening of nutritional status to identify patients at risk for adverse outcomes due to malnutrition; (2) address optimal methods of providing nutritional support and optimizing nutrition status preoperatively; and (3) identifying when and how to optimize nutrition delivery in the postoperative period. Discussion led to strong recommendations for implementation of routine preoperative nutrition screening to identify patients in need of preoperative nutrition optimization. Postoperatively, nutrition delivery should be restarted immediately after surgery. The key role of oral nutrition supplements, enteral nutrition, and parenteral nutrition (implemented in that order) in most perioperative patients was advocated for with protein delivery being more important than total calorie delivery. Finally, the role of often-inadequate nutrition intake in the posthospital setting was discussed, and the role of postdischarge oral nutrition supplements was emphasized.

First report of three Kudoa species from eastern Australia: Kudoa thyrsites from mahi mahi (Coryphaena hippurus), Kudoa amamiensis and Kudoa minithyrsites n. sp. from sweeper (Pempheris ypsilychnus)

Fish species around the world are parasitized by myxozoans of the genus Kudoa, several of which infect and cause damage of commercial importance. In particular, Kudoa thyrsites and Kudoa amamiensis infect certain cultured fish species causing damage to muscle tissue, making the fish unmarketable. Kudoa thyrsites has a broad host and geographic range infecting over 35 different fish species worldwide, while K. amamiensis has only been reported from a few species in Japanese waters. Through morphological and molecular analyses we have confirmed the presence of both of these parasites in eastern Australian waters. In addition, a novel Kudoa species was identified, having stellate spores, with one polar capsule larger than the other three. The SSU rDNA sequence of this parasite was 1.5% different from K. thyrsites and is an outlier from K. thyrsites representatives in a phylogenetic analysis. Furthermore, the spores of this parasite are distinctly smaller than those of K. thyrsites, and thus it is described as Kudoa minithyrsites n. sp. Although the potential effects of K. minithyrsites n. sp. on its fish hosts are unknown, both K. thyrsites and K. amamiensis are associated with flesh quality problems in some cultured species and may be potential threats to an expanding aquaculture industry in Australia.

Whole-body cortisol response of zebrafish to acute net handling stress

Zebrafish, Danio rerio, are frequently handled during husbandry and experimental procedures in the laboratory, yet little is known about the physiological responses to such stressors. We measured the whole-body cortisol levels of adult zebrafish subjected to net stress and air exposure at intervals over a 24 h period; cortisol recovered to near control levels by about 1 h post-net-stress (PNS). We then measured cortisol at frequent intervals over a 1 h period. Cortisol levels were more than 2-fold higher in net stressed fish at 3 min PNS and continued to increase peaking at 15 min PNS, when cortisol levels were 6-fold greater than the control cortisol. Mean cortisol declined from 15 to 60 min PNS, and at 60 min, net-stressed cortisol was similar to control cortisol. Because the age of fish differed between studies, we examined resting cortisol levels of fish of different ages (3, 7, 13, and 19 months). The resting cortisol values among tanks with the same age fish differed significantly but there was no clear effect of age. Our study is the first to report the response and recovery of cortisol after net handling for laboratory-reared zebrafish.

Biodiversity: disease threat to European fish

The deliberate introduction of new species can have unexpected negative consequences and we show here how a recently introduced fish, the invasive Asian cyprinid Pseudorasbora parva, is causing increased mortality and totally inhibiting spawning in an already endangered native fish, the European cyprinid Leucaspius delineatus. This threat is caused by an infectious pathogen, a rosette-like intracellular eukaryotic parasite that is a deadly, non-specific agent. It is probably carried by healthy Asian fish, and could decrease fish biodiversity in Europe, as well as having implications for commercial aquaculture.

Phylogeography of the cosmopolitan marine parasite Kudoa thyrsites (Myxozoa: Myxosporea)

Kudoa thyrsites (Myxozoa: Multivalvulida) is a cosmopolitan marine parasite of fishes associated with post-mortem tissue degradation. Financial losses incurred as a result of these infections are of concern to commercial fisheries. There is conflicting evidence whether K. thyrsites represents a cryptic species complex. Myxospore morphology is very similar for K. thyrsites across its range, but preliminary genetic analyses show some differences. Kudoa thyrsites and the morphologically similar Kudoa histolytica were examined from hosts in British Columbia, Canada, Oregon, USA, Chile, England, South Africa, Australia, and Japan. We compared myxospore morphology and DNA sequences of heat shock protein 70 and the small subunit, large subunit, and internal transcribed spacer 1 of the ribosomal DNA. There was some morphological variation between regional representatives, inconsistent with genetic analyses. Phylogenetically, major separations correlated to four broad geographic regions: Japan, Australia, eastern Pacific, and eastern Atlantic. Within these regions there was little additional genetic structure. These data are evidence for regional subdivision of K. thyrsites suggesting global transplantation of fishes has yet to homogenize these distinctions. Within regions, parasite gene flow appears to be high between host species, suggesting little host specificity and minimal cryptic speciation. Our data also indicate that K. histolytica is not a valid species, as it was morphologically and genetically indistinguishable from K. thyrsites.

Phylogeny of the multivalvulidae (Myxozoa: Myxosporea) based on comparative ribosomal DNA sequence analysis

Fish parasites of the Multivalvulida (Myxozoa, Myxosporea) are widespread and can be associated with mortality or poor flesh quality in their commercially important marine hosts. Traditional classifications divide members of this order into families based on spore valve and polar capsule numbers. Analyses of the small-subunit (SSU) ribosomal DNA (rDNA) sequences from all representative families in the order (Trilosporidae, Kudoidae, Pentacapsulidae, Hexacapsulidae, and Septemcapsulidae) indicate that a revision of the taxonomy and nomenclature is warranted. In our phylogenetic analysis of (SSU and large subunit) rDNA sequences, members of Pentacapsula, Hexacapsula, and Septemcapsula root within a clade of Kudoa species with Unicapsula (Trilosporidae) as an outlier to these genera. Therefore, we propose to synonymize Pentacapsulidae, Hexacapsulidae, and Septemcapsulidae with Kudoidae alter the diagnosis of Kudoidae and Kudoa to accommodate all marine myxozoan parasites having 4 or more shell valves and polar capsules.

Bioaccumulation and clearance of microcystins from salt water mussels, Mytilus edulis, and in vivo evidence for covalently bound microcystins in mussel tissues

Over a period of 3 days saltwater mussels, Mytilus edulis, were fed a cyanobacteria, Microcystis aeruginosa, that contained a high concentration of microcystins. The mussels were killed on a periodic basis over the course of 2 months. Mussels were also collected at two sites were high levels of microcystins in tissues had been noted. A strategy based on the chemically unique nature of the C20 beta-amino acid, (2S,3S,8S,9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6- dienoic acid (Adda), portion of the microcystins was used in conjunction with a protein phosphatase (PPase) assay to analyse for both covalently bound microcystins and free microcystins in the mussel tissues. The mussel PPase assay results were compared with the Lemieux oxidation gas chromatography-mass spectrometry (GCMS) analysis. Less than 0.1% of the total microcystin burden in the mussel tissue was found to be extractable with MeOH. Thus, direct evidence was provided for the existence of covalently bound microcystins in mussel tissues in vivo. The mussels rapidly cleared the covalently bound microcystins when transferred to untreated seawater. Within 4 days the total microcystin burden dropped from a high of 336.9 (+/- 45.8) micrograms/g wet tissue to 11.3 (+/- 2.6) micrograms/g. After 4 days postexposure until completion of the experiment the total levels remained below the detection limits of the GCMS method. The levels of free microcystins, extracted with MeOH and detected by the PPase assay, fell from 204 ng/g wet tissue to a residual 14 ng/g over a 53 day postexposure period. Presumably the bound microcystin present in the mussel tissue exists as a covalent complex with the PP-1 and PP-2A enzymes. We conclude that in any shellfish monitoring program it is the total tissue microcystin burden that needs to be considered.

Nonlesions, Misdiagnoses, Missed Diagnoses, and Other Interpretive Challenges in Fish Histopathology Studies

Differentiating salient histopathologic changes from normal anatomic features or tissue artifacts can be decidedly challenging, especially for the novice fish pathologist. As a consequence, findings of questionable accuracy may be reported inadvertently, and the potential negative impacts of publishing inaccurate histopathologic interpretations are not always fully appreciated. The objectives of this article are to illustrate a number of specific morphologic findings in commonly examined fish tissues (e.g., gills, liver, kidney, and gonads) that are frequently either misdiagnosed or underdiagnosed, and to address related issues involving the interpretation of histopathologic data. To enhance the utility of this article as a guide, photomicrographs of normal and abnormal specimens are presented. General recommendations for generating and publishing results from histopathology studies are additionally provided. It is hoped that the furnished information will be a useful resource for manuscript generation, by helping authors, reviewers, and readers to critically assess fish histopathologic data.

Molecular and morphological analysis of Myxobolus spp. of salmonid fishes with the description of a new Myxobolus species

While investigating the parasite fauna of wild coho salmon. Oncorhynchus kisutch (Walbaum, 1792), histological examination provided evidence of a new species of Myxobolus (Myxozoa: Myxosporea) infecting nerves of skeletal muscle. Spores were morphologically similar to those of the intramuscular Myxobolus insidiosus Wyatt and Pratt, 1963, both having pyriform spores with clavate polar capsules. However, the former developed exclusively in the nerves of skeletal muscle rather than in myocytes. We examined both species of Myxobolus derived from coho salmon; Chinook salmon, Oncorhynchus tshawytscha (Walbaum, 1792); cutthroat trout, Oncorhynchus clarkii (Richardson, 1836); and rainbow trout Oncorhynchus mykiss (Walbaum, 1792) from freshwater in Oregon. Spore morphology, small subunit ribosomal RNA gene (rDNA) sequences, and site of infection were compared. Myxobolus arcticus Pugachev and Khokhlov, 1979 has pyriform spores, infects the central nervous system of many salmonids, and is found in the Pacific Northwest. It was therefore included in the analyses to rule out conspecificity with the new species. Together, these data show that the Myxobolus sp. from peripheral nerves in the skeletal musculature of coho salmon, rainbow trout, and cutthroat trout is a new species, described herein as Myxobolus fryeri n. sp.

American Society for Enhanced Recovery and Perioperative Quality Initiative-4 Joint Consensus Statement on Persistent Postoperative Opioid Use: Definition, Incidence, Risk Factors, and Health Care System Initiatives

Persistent postoperative opioid use is thought to contribute to the ongoing opioid epidemic in the United States. However, efforts to study and address the issue have been stymied by the lack of a standard definition, which has also hampered efforts to measure the incidence of and risk factors for persistent postoperative opioid use. The objective of this systematic review is to (1) determine a clinically relevant definition of persistent postoperative opioid use, and (2) characterize its incidence and risk factors for several common surgeries. Our approach leveraged a group of international experts from the Perioperative Quality Initiative-4, a consensus-building conference that included representation from anesthesiology, surgery, and nursing. A search of the medical literature yielded 46 articles addressing persistent postoperative opioid use in adults after arthroplasty, abdominopelvic surgery, spine surgery, thoracic surgery, mastectomy, and thoracic surgery. In opioid-naïve patients, the overall incidence ranged from 2% to 6% based on moderate-level evidence. However, patients who use opioids preoperatively had an incidence of >30%. Preoperative opioid use, depression, factors associated with the diagnosis of substance use disorder, preoperative pain, and tobacco use were reported risk factors. In addition, while anxiety, sex, and psychotropic prescription are associated with persistent postoperative opioid use, these reports are based on lower level evidence. While few articles addressed the health policy or prescriber characteristics that influence persistent postoperative opioid use, efforts to modify prescriber behaviors and health system characteristics are likely to have success in reducing persistent postoperative opioid use.

The state of the art of the zebrafish model for toxicology and toxicologic pathology research--advantages and current limitations

The zebrafish (Danio rerio) is now the pre-eminent vertebrate model system for clarification of the roles of specific genes and signaling pathways in development. The zebrafish genome will be completely sequenced within the next 1-2 years. Together with the substantial historical database regarding basic developmental biology, toxicology, and gene transfer, the rich foundation of molecular genetic and genomic data makes zebrafish a powerful model system for clarifying mechanisms in toxicity. In contrast to the highly advanced knowledge base on molecular developmental genetics in zebrafish, our database regarding infectious and noninfectious diseases and pathologic lesions in zebrafish lags far behind the information available on most other domestic mammalian and avian species, particularly rodents. Currently, minimal data are available regarding spontaneous neoplasm rates or spontaneous aging lesions in any of the commonly used wild-type or mutant lines of zebrafish. Therefore, to fully utilize the potential of zebrafish as an animal model for understanding human development, disease, and toxicology we must greatly advance our knowledge on zebrafish diseases and pathology.

Chemical and biological evidence links microcystins to salmon 'netpen liver disease'

Evidence is presented that links microcystins to a severe liver disease that occurs in Atlantic salmon that are netpen-reared in coastal British Columbia. Liquid chromatography-linked protein phosphatase bioassay analysis of extracts of liver tissue taken from Atlantic salmon afflicted with netpen liver disease showed the presence of an inhibitor of protein phosphatase that was chromatographically indistinguishable from microcystin-LR. Analysis of liver tissue from healthy control fish showed a complete absence of microcystin-LR. Intraperitoneal injection of microcystin-LR into healthy Atlantic salmon re-created the pathologic changes of netpen liver disease, including diffuse necrosis and hepatic megalocytosis.

Evidence for a covalently bound form of microcystin-LR in salmon liver and Dungeness crab larvae

The chemically unique nature of the C20 beta-amino acid (2S,3S,8S,9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6- dienoic acid (Adda) portion of the microcystins has been exploited to develop a strategy to analyze for the total microcystin-LR (1; see Figure 1) burden in salmon liver and crab larvae tissues. Lemieux oxidation of microcystin-LR (1) gives 2-methyl-3-methoxy-4-phenylbutanoic acid (2), a unique marker for the presence of microcystins. The butanoic acid 2 can be isolated and detected by GC/MS from the livers of Atlantic salmon that received an ip injection of microcystin-LR (1) and from tissues of wild-caught crab larvae. The Lemieux oxidation-GC/MS results are compared with those from MeOH extraction-PPase analysis. Only approximately 24% of the total microcystin-LR (1) burden in salmon liver tissue is found to be extractable with MeOH. Similarly, the Lemieux oxidation-GC/MS method detected 10,000-fold greater microcystin concentrations in Cypress Island Dungeness crab larvae than did the MeOH extraction-PPase method. The disparity in microcystin concentrations measured by the two methods is taken as direct evidence for the existence of covalently bound microcystins in vivo.

A NEW SPECIES OF SPHAEROMYXA (MYXOSPOREA: SPHAEROMYXINA: SPHAEROMYXIDAE) IN DEVIL FIREFISH, PTEROIS MILES (SCORPAENIDAE), FROM THE NORTHERN RED SEA: MORPHOLOGY, ULTRASTRUCTURE, AND PHYLOGENY

Sphaeromyxa zaharoni n. sp. (Myxosporea) is described from the gallbladder of devil firefish, Pterois miles (Scorpaenidae), from coral reefs of the Gulf of Eilat, Israel, northern Red Sea. The parasite was found also in bearded scorpionfish, Scorpaenopsis barbata, from the same area. This is the first report on Sphaeromyxa sp. from this zoogeographical region. The plasmodia are amoeboid when young, becoming disc-shaped and elongated when mature. In paraffin sections, the plasmodium periphery appears as a finely granulated, strongly eosinophilic layer with an intricate surface membrane network. Sphaeromyxa zaharoni n. sp. is polysporous, disporoblastic, and has asynchronous sporogenesis. The mature spore is elongated and fusiform, has delicately ridged valves, and contains a single, binucleated sporoplasm. In valvular view, the tips are truncated. The mean spore size is length 14.5 microm, width 4.8 microm, and polar capsule 4.8 x 3.4 microm. The 2 equally sized ovoid polar capsules are positioned at opposite ends of the spore, each containing a filament loosely folded in 2 loops. The fine structure of the sporoblast and spore corresponded with previously studied Sphaeromyxa species. According to small-subunit ribosomal DNA gene sequence analysis, S. zaharoni n. sp. is most closely related to 2 Myxidium spp. The close phylogenetic relatedness of Sphaeromyxa and Myxidium and similar spore morphology raises the question whether these 2 genera should be maintained in separate families and suborders.

H. pylori virulence factor CagA increases intestinal cell proliferation by Wnt pathway activation in a transgenic zebrafish model

Infection with Helicobacter pylori is a major risk factor for the development of gastric cancer, and infection with strains carrying the virulence factor CagA significantly increases this risk. To investigate the mechanisms by which CagA promotes carcinogenesis, we generated transgenic zebrafish expressing CagA ubiquitously or in the anterior intestine. Transgenic zebrafish expressing either the wild-type or a phosphorylation-resistant form of CagA exhibited significantly increased rates of intestinal epithelial cell proliferation and showed significant upregulation of the Wnt target genes cyclinD1, axin2 and the zebrafish c-myc ortholog myca. Coexpression of CagA with a loss-of-function allele encoding the β-catenin destruction complex protein Axin1 resulted in a further increase in intestinal proliferation. Coexpression of CagA with a null allele of the key β-catenin transcriptional cofactor Tcf4 restored intestinal proliferation to wild-type levels. These results provide in vivo evidence of Wnt pathway activation by CagA downstream of or in parallel to the β-catenin destruction complex and upstream of Tcf4. Long-term transgenic expression of wild-type CagA, but not the phosphorylation-resistant form, resulted in significant hyperplasia of the adult intestinal epithelium. We further utilized this model to demonstrate that oncogenic cooperation between CagA and a loss-of-function allele of p53 is sufficient to induce high rates of intestinal small cell carcinoma and adenocarcinoma, establishing the utility of our transgenic zebrafish model in the study of CagA-associated gastrointestinal cancers.

Molecular systematics support the revival of Mycobacterium salmoniphilum (ex Ross 1960) sp. nov., nom. rev., a species closely related to Mycobacterium chelonae

Mycobacterial infections in fish are usually attributed to strains of Mycobacterium marinum, Mycobacterium chelonae and Mycobacterium fortuitum. Bacteria identified as M. chelonae have been isolated numerous times from salmonid fishes. Recently, this bacterium has been associated with salmon mortalities in the aquaculture industry. An M. chelonae-like species from salmon, 'Mycobacterium salmoniphilum', was described in 1960. However, the species name lost standing in nomenclature when it was omitted from the 1980 Approved Lists of Bacterial Names because the species could not be distinguished with confidence from M. fortuitum. In the 1980s, mycobacteria isolated from salmon were characterized as a distinct subspecies, 'Mycobacterium chelonae subsp. piscarium'. Again, the uncertainty of the validity of the species resulted in the subsequent withdrawal of the name. Since then, most studies have considered isolates from salmon to be M. chelonae. Nucleotide sequence analysis of the small-subunit rRNA, hsp65 and rpoB genes was used to examine the taxonomic relatedness of type cultures and authentic isolates in our culture collection available from earlier studies. The M. chelonae-like strains from salmon were phylogenetically distinct from other Mycobacterium strains and members of the M. chelonae complex. Moreover, the cell-wall-bound mycolic acids were not representative of known mycolate patterns for M. chelonae-complex organisms. These results supported the status of the species as a separate taxon and effect the valid publication of the name 'M. salmoniphilum' as Mycobacterium salmoniphilum (ex Ross 1960) sp. nov., nom. rev., with the type strain SCT (=ATCC 13578T =DSM 43276T).

Pseudoloma neurophilia n. g., n. sp., a new microsporidium from the central nervous system of the zebrafish (Danio rerio)

An unusual xenoma-forming microsporidium was discovered in the central nervous system of moribund zebrafish from a laboratory colony in Eugene, Oregon. Infected fish were often emaciated and lethargic, and histological examination commonly revealed severe myelitis and myositis associated with the infection. Based on its structure, development, and small subunit ribosomal DNA sequence it is unique among fish microsporidia. Spores are uninucleate, ovoid to pyriform, with a prominent posterior vacuole. Spores average 5.4 x 2.7 microm with 13-16 coils of the polar filament. The microsporidium produces xenomas within the spinal cord and hindbrain of fish, and xenomas contained sporophorous vesicles with up to 16 spores. Sporoblasts and presporoblast stages (probably sporonts) are found occasionally in small aggregates dispersed randomly throughout xenomas. It clustered in the "Ichthyosporidium group" along with other fish microsporidian genera based on rDNA sequence analysis. The rDNA sequence of the zebrafish microsporidium was most similar to that of Ichthyosporidium, but showed only 12.1% similarity and therefore this microsporidium can be considered a distinct genus and species, which we have named Pseudoloma neurophilia n. g., n. sp.

14C-labeled microcystin-LR administered to Atlantic salmon via intraperitoneal injection provides in vivo evidence for covalent binding of microcystin-LR in salmon livers

The tissue distribution and clearance of radiolabeled microcystin-LR administered to Atlantic salmon via i.p. injection has been re-examined using uniformly 14C-labeled toxin. Significant differences were found to exist between these results and those obtained when fish received an i.p. injection of tritium-labeled dihydromicrocystin-LR. In addition, MeOH liver extracts were assayed by both phosphatase assay and 14C counts and the results compared with the total levels of incorporation determined by digestion and subsequent 14C counting of the same live tissues. An attempt to investigate the metabolism and to document the putative products was also undertaken. It was found that microcystin-LR was extensively metabolized to compounds that are more polar than the parent compound.

Two unusual myxozoans, Kudoa quadricornis n. sp. (Multivalvulida) from the muscle of goldspotted trevally (Carangoides fulvoguttatus) and Kudoa permulticapsula n. sp. (Multivalvulida) from the muscle of Spanish mackerel (Scomberomorus commerson) from the Great Barrier Reef, Australia

Two unusual myxozoan parasites are described from the somatic muscle of 2 reef fishes from Australia's Great Barrier Reef. Kudoa quadricornis n. sp. from the somatic muscle of Carangoides fulvoguttatus is morphologically consistent with other Kudoa sp., having 4 polar capsules and 4 shell valves. Kudoa quadricornis n. sp. is unique in that it has a pyriform spore body with a greater length than width (7.82-9.95 and 5.94-8.66 microm, respectively) and distinct posterolateral projections. Spores of Kudoa permulticapsula n. sp. observed within pseudocysts of the somatic muscle tissue of Scomberomorus commerson are different from those of all other myxozoans. The ovoid spores (length, 4.69-6.65 microm; width, 8.42-9.92 microm; thickness, 6.36-8.33 microm) contain 13 polar capsules with an equal number of shell valves. Phylogenetic analysis using small subunit ribosomal DNA sequences of K. quadricornis n. sp. and K. permulticapsula n. sp. showed that these parasites cluster within a clade comprised of Kudoa species. This brings into question the division of parasites of the Multivalvulida into genera based solely on polar capsule numbers.

Pseudoloma neurophilia infections in zebrafish Danio rerio: effects of stress on survival, growth, and reproduction

Pseudoloma neurophilia (Microsporidia) is a common disease of zebrafish Danio rerio, including those used as research models. We conducted a study comprised of 4 separate experiments to determine the effects of husbandry stress on preexisting and experimental P. neurophilia infections and the subsequent effects on survival, infection onset and intensity, fish growth, and reproduction. In fish (AB strain) with preexisting infections, stress or feeding cortisol significantly increased mortality over 7 wk compared to no stress or cortisol treatment. In contrast, no mortality was observed in fish (TL strain) experimentally exposed to P. neurophilia over 10 wk. A third experiment involved experimental exposure of AB fish to P. neurophilia and exposure to crowding and handling stressors. No mortality was associated with P. neurophilia regardless of stress treatment over a period of 20 wk. However, the onset of infection occurred sooner in stress-treated fish. Stress significantly increased the mean intensity of infection (described as xenoma area/spinal cord area in histological sections) at Week 20 post-exposure (PE). In fish with preexisting infections, myositis was significantly greater in stressed and cortisol-treated fish than those not stressed. With experimental exposure of AB fish, stressed and infected groups weighed significantly less than the control group at Week 20 PE. Regarding fecundity, the number of larvae hatched at 5 d post fertilization was negatively associated with mean infection intensity among P. neurophilia-infected and stressed AB fish. These experiments are the first to show empirically that P. neurophilia can be associated with reduced weight and fecundity, and that stress can exacerbate the severity of the infection.

Documented and potential research impacts of subclinical diseases in zebrafish

The zebrafish (Danio rerio) has become a very important animal model in biomedical research. In contrast with other models, such as mice, there has been relatively little documentation or control of subclinical disease in zebrafish research facilities. Several infectious and noninfectious conditions are consistently detected by histopathology in apparently healthy D. rerio. The most commonly observed infectious agent in zebrafish is Pseudoloma neurophilia, which is a microsporidian organism that targets the central nervous system, peripheral nerves, and occasionally other tissues. Mycobacteriosis, caused by Mycobacterium chelonae and other species, is also a frequent finding. Less commonly encountered agents include Pseudocapillaria tomentosa, which can cause extensive proliferative enteritis, and a myxozoan (Myxidium sp.) that inhabits the urinary tract but appears to cause few if any pathological changes. Noninfectious diseases that are often clinically unapparent in zebrafish include hepatic megalocytosis, bile and pancreatic ductal proliferation, and neoplasms of the ultimobranchial gland, gastrointestinal tract, and testis. To date, there is little information on the degree to which these conditions may impact research in subclinically affected fish, but there is reason to believe that they should be considered as potentially significant causes of nonprotocol variation in experiments. Therefore, it is imperative that research facilities monitor their stocks for the presence of these occult diseases and be aware of their existence when interpreting study results. Furthermore, for underlying disease conditions that cannot be readily eradicated, it is essential to determine the physiological and immunological changes that they elicit in zebrafish. Understanding the cause, modes of transmission, and distribution of the pathogens would provide useful information for the development of control and prevention strategies.

Mycobacteriosis in zebrafish (Danio rerio) research facilities

The Zebrafish International Resource Center was established to support the zebrafish research community, and includes a diagnostic service. One of the most common diseases that we have diagnosed is mycobacteriosis, which represented 18% of the diagnostic cases submitted from November 1999 to June 2003. We describe here the severity of the disease and associated pathological changes of 24 diagnostic cases from 14 laboratories. Identifications of the bacteria are provided for seven of these cases. For two cases in which culture of the organism was not successful, these identifications were based on ribosomal DNA (rDNA) sequence analysis obtained directly from infected tissues. Biochemical characteristics and rDNA sequence analysis from cultures are reported for the other isolates. Two severe outbreaks from different facilities on different continents were associated with an organism identified as Mycobacterium haemophilum based on rDNA sequence from tissues. Another severe outbreak was associated with an organism most closely related to Mycobacterium peregrinum. These species are recognized pathogens of humans, but this is the first report of them from fish. Bacteria identified as Mycobacterium chelonae or M. abscessus were recovered from fish in cases categorized as moderate disease or as an incidental finding. These findings indicate that species of Mycobacterium previously undescribed from fish (i.e., M. haemophilum and M. peregrinum) may pose significant health problems in zebrafish research facilities, whereas species and strains that are already recognized as common in fish usually cause limited disease on a population basis in zebrafish.