A microsporidian parasite of the genus Spraguea in the nervous tissues of the Japanese anglerfish Lophius litulon

Development of a novel assay for extensive characterization of the germination conditions of Spraguea americanus: a microsporidian parasite of the American anglerfish (Lophius americanus)

The microsporidia are a widespread group of intracellular parasites which infect a broad range of hosts across the animal kingdom. In particular, the microsporidian Spraguea americanus has received considerable attention in recent years due to its role as an endemic pathogen in American anglerfish (Lophius americanus), a species of highly valued finfish currently at risk due to overfishing. However, like many species of microsporidia, the germination responses of S. americanus remain poorly described. This study outlines a novel in vitro germination assay for microsporidians, which is then used to comprehensively survey the germination responses of S. americanus under a variety of conditions. The results of this investigation indicate that S. americanus is responsive to mechanical pressure, hydrogen peroxide, sodium carbonate/bicarbonate and divalent cations, but not to mucus or mucin proteins as seen in closely related species. These observations provide evidence to refute the predominant hypothesis that members of Spraguea enter their hosts via the subcutaneous mucosal glands. In addition to providing much needed insight into the transmission of Spraguea spp., this study is among the first to extensively assess the germination responses of a single species of microsporidia; data which may lend itself to a more complete understanding of the mechanisms underlying the initiation of germination in microsporidia or support the establishment of new in vitro models for economically relevant species.

Heterocapsa cf. bohaiensis (dinoflagellate): identification and response to nickel and iron stress revealed through chlorophyll a fluorescence

Metal toxicity in marine ecosystems is a growing issue owing to terrestrial runoff and anthropogenic pollution. Heterocapsa cf. bohaiensis, a newly isolated dinoflagellate from New Caledonia, was cultivated in photobioreactors operating continuously with high concentrations of nickel (1.70 10-5M) (Ni2+) and/or iron (1.79 10-5M) (Fe2+) and their photosynthetic efficiency was assessed. The photosynthetic measurements indicated that H. cf. bohaiensis was tolerant to Ni2+ but sensitive to Fe2+ high concentrations. In the presence of Fe2+, maximum quantum efficiency and maximal relative electron transport rate decreased from 0.62 to 0.47 and from 156 to 102, respectively. The JIP-tests suggested a reduction of the photosynthesis in response to Fe2+ due to a disruption in the electron transport chain rather than a defect in the light absorption and trapping capacity which were on the contrary enhanced by Fe2+. These results bring new knowledge on the impact of nickel and iron on microalgae photosynthetic pathways.

A new microsporidian parasite, Microsporidium theragrae n. sp., infecting Alaska pollock Gadus chalcogrammus (Teleostei: Gadidae)

A new microsporidian infecting Gadus chalcogrammus Pallas, 1814 (Gadidae), is described based on morphological, ultrastructural, and molecular studies. This microsporidian parasite develops inside intramuscular spindle-shaped lesions measuring approximately 1-2 mm in width and 4-8 mm in length. Infected cells encapsulated by a host-produced wall containing a sponge-like acellular zone. Sporogony presumably proceeds via segmentation of sporogonial plasmodium, resulting in a variable number of spores. Sporogonial stages develop in sporophorous vesicles (SVs), abutting a moderately electron-dense thick walled coat of a homogeneous amorphous material. SVs space contains rare granular and tubular inclusions. Neighboring SVs often interconnected by bridges of the host cell cytoplasm that were limited by membrane comparable with SV coat. The elongate-ovoid spores, measuring 4.29 ± 0.38 × 2.51 ± 0.26 μm (N 104), possess a bipartite polaroplast and polar tube with 15-16 coils arranged in 2-3 layers. The angle of tilt of the polar tube coils is less than 30°. The sequence analysis of SSU rDNA coding region showed that the studied microsporidians differs from other fish muscle-infecting species at least in 17 bp (2.58%) and is closely related to Microsporidium cypselurus Yokoyama et al. (2002) infecting the flying fish from East China Sea. The parasite is provisionally positioned as Microsporidium theragrae sp. n.

Microsporidia Have a Peculiar Outer Membrane with Exterior Cytoplasmic Proteins

PURPOSE

Most eukaryotic cells have a plasma membrane with glycoproteins on the outer leaflet and cytoplasmic proteins on the inner leaflet. However, the microsporidians examined have a peculiar outer membrane with cytoplasmic proteins on the surface. His study was to determine if this is true and identify the presence of key cytoplasmic proteins on the exterior of the sporoplasm and spore stages.

METHODS

Specific probes including GFP-labeled genes, antibodies, and electron microscopy were applied to studies on the sporoplasm and spore stages of different microsporidian species.

RESULTS

Cytoplasmic membrane proteins cadherin, intermediate filaments, dynactin p150Glued and tubulin were identified on the outer leaflet of the exterior membrane of the sporoplasm or spore stages of Spraguea americanus, Anncaliia algerae, Ameson michaelis and Thelohania sp.

CONCLUSION

The invasive sporoplasm stage of microsporidians acquires an outer membrane from a cytoplasmic organelle and it has been shown that the outside surface of this membrane bears cytoplasmic proteins. This membrane retains these cytoplasmic proteins even on the spore stage. For an intracellular parasite that locates directly within the cytoplasm of a host cell, the presence of these cytoplasmic proteins on the surface of the parasite appears to have a significant effect on the host's response.

Microsporidia Can Acquire Lamin-like Intermediate Filaments and Cell Adhesion Catenin-cadherin Complexes from the Host (?)

On their spore surfaces, Microsporidia often develop a canopy of filaments with characteristics of intermediate filaments (IF), as we demonstrated in previous studies on Thelohania sp., Ameson michaelis, and Spraguea lophii. Genomic studies indicate that among invertebrates, lamins that may localize in the cytoplasm or nucleus, are the only known IF type. These IFs can bind to the substrate containing cell adhesion molecules (CAMs) cadherins, associated with β and γ catenins. The objects of this study were to determine whether microsporidia have CAMs with the attached IFs on their envelopes and to find out if these proteins are provided by the host. An examination was made for localization of lamins and CAMs on the spores of the mentioned above species and Anncaliia algerae, plus in the host animals. Then, we determined whether the spores of A. michaelis and A. algerae could bind vertebrate nuclear lamin onto the spore surface. We also tested transgenic Drosophila melanogaster stocks bearing cadherin-GFP to see whether developing A. algerae parasites in these hosts could acquire host CAMs. The tests were positive for all these experiments. We hypothesize that microsporidia are able to acquire host lamin IFs and cell adhesion catenin-cadherin complexes from the host.

Microsporidians xenomas of anglerfish from NE Atlantic waters

The presence of emergent visible parasites at commercial valuable fish species is increasingly causing problems at fisheries and seafood industries. Microsporidians have been previously reported to appear forming apparent xenomas complexes in anglerfish species, but no effort has been carried out to simultaneously integrate epidemiological data, phenotypic, genotypic and fine structural characterizations in the same parasite sample. In this work, specimens of Lophius budegassa and Lophius piscatorius from NE Atlantic waters were sampled and examined to provide information about specific site of infection and demographic data of two groups of different sizes of xenomas present at both fish species. Histological descriptions and scanning and transmission electron microscopy were carried out on fresh spores of Lophius budegassa for ultrastructural studies. In both types of xenomas, it was observed simultaneously the microsporidian genus Spraguea in the form of two different types of spores. Molecular analyses of both xenomas from the two fish species, based on the small subunit ribosomal DNA gene, were also performed to genetically support the morphological diagnostic provided.

A Recent Whole-Genome Duplication Divides Populations of a Globally Distributed Microsporidian

The Microsporidia are a major group of intracellular fungi and important parasites of animals including insects, fish, and immunocompromised humans. Microsporidian genomes have undergone extreme reductive evolution but there are major differences in genome size and structure within the group: some are prokaryote-like in size and organisation (<3 Mb of gene-dense sequence) while others have more typically eukaryotic genome architectures. To gain fine-scale, population-level insight into the evolutionary dynamics of these tiny eukaryotic genomes, we performed the broadest microsporidian population genomic study to date, sequencing geographically isolated strains of Spraguea, a marine microsporidian infecting goosefish worldwide. Our analysis revealed that population structure across the Atlantic Ocean is associated with a conserved difference in ploidy, with American and Canadian isolates sharing an ancestral whole genome duplication that was followed by widespread pseudogenisation and sorting-out of paralogue pairs. While past analyses have suggested de novo gene formation of microsporidian-specific genes, we found evidence for the origin of new genes from noncoding sequence since the divergence of these populations. Some of these genes experience selective constraint, suggesting the evolution of new functions and local host adaptation. Combining our data with published microsporidian genomes, we show that nucleotide composition across the phylum is shaped by a mutational bias favoring A and T nucleotides, which is opposed by an evolutionary force favoring an increase in genomic GC content. This study reveals ongoing dramatic reorganization of genome structure and the evolution of new gene functions in modern microsporidians despite extensive genomic streamlining in their common ancestor.

Inaccuracy of Labeling and Visual Inspection for Microsporidian Parasites in Anglerfish Lophius litulon (Jordan, 1902) Collected from Chinese Retail Markets in Sardinia, Italy

The aim of the present study was to evaluate the accuracy of labeling and the efficacy of visual inspection to detect the lesions by visible parasites in anglerfish Lophius litulon. One hundred samples were collected over a 2-year period (2011 to 2012) from Chinese retail markets in Sardinia, Italy. To assess the conformity of the items with the trade name, a preliminary visual inspection of the samples by a simple morphological analysis was performed. According to the Council Regulations (EC) 104/2000, 1224/2009, and 2074/2005, the Italian labels were examined to verify the appropriate indication of relevant information on traceability (trade name, scientific name, geographical area, and production method), and the samples of L. litulon were subjected to visual inspection to detect "visible parasites." Altogether, a high percentage of mismatching (70%) between the scientific name and trade name was pointed out. Moreover, 60% of the samples were visibly infected by Spraguea lophii, a microsporidian parasite of the nervous tissue that forms typical lesions (xenomas) in the fish flesh near the vertebral column. Although S. lophii is not pathogenic to humans, the presence of xenomas can decompose the fish flesh and render it unfit for human consumption. The high percentage of mislabeling, together with the inaccuracy in the visual inspection by Chinese food business operators highlighted the need to improve the European Union control system of fishery products imported from China and marketed in Europe.

Zoothamnium duplicatum infestation of cultured horseshoe crabs (Limulus polyphemus)

An outbreak of the sessile peritrich Zoothamnium duplicatum in a pilot, commercial-scale Limulus polyphemus hatchery resulted in the loss of ∼96% (40,000) second/third instar larvae over a 61day period. peritrich growth was heavy, leading to mechanical obstruction of the gills and physical damage. The peritrichs were controlled without resultant loss of juvenile crabs by administering 10ppm chlorine in freshwater for 1h and the addition of aquarium grade sand; a medium into which the crabs could burrow and facilitate cleaning of the carapace. Peritrich identity was confirmed from a partial SSU rDNA contiguous sequence of 1343bp (99.7% similarity to Z. duplicatum).

Multiple gene analyses of caligid copepods indicate that the reduction of a thoracic appendage in Pseudocaligus represents convergent evolution

BACKGROUND

The Caligidae is a family of parasitic copepods containing over 30 recognised genera. They are commercially important parasites as they cause disease in numerous finfish aquaculture facilities globally. Morphological features are used to distinguish between the genera and Pseudocaligus has traditionally been differentiated from Caligus solely by the presence of a much reduced form of the fourth thoracic leg. Currently there are numerous DNA sequences available for Caligus spp. but only the type species, Pseudocaligus brevipedis, has molecular data available, so systematic studies using molecular phylogenetic analyses have been limited.

METHODS

Three gene regions, SSU rDNA, 16S and CO1, for Pseudocaligus fugu from puffer fish from Japan and Pseudocaligus uniartus from rabbit fish from Indonesia are sequenced and molecular phylogenetic analyses performed in order to infer phylogenetic relationships between Pseudocaligus and other caligid copepods.

RESULTS

The analysis revealed that there was no discrete grouping of Pseudocaligus spp. and that they had a polyphyletic distribution within Caligus taxa. Pseudocaligus fugu grouped with Caligus elongatus and contained a unique synapomorphy in the SSU rDNA region only seen in members of that clade. Pseudocaligus uniartus formed a well-supported group, in the SSU rDNA analyses, with a Caligus sp. that also infects rabbit fish, but was unresolved in the other analyses. Pseudocaligus brevipedis consistently and robustly grouped with Caligus curtus and C. centrodonti in all analyses. The majority of Lepeophtheirus spp. form a monophyletic sister group to the Caligus clade; however, L. natalensis is unresolved in all analyses and does not form part of the main Lepeophtheirus clade.

CONCLUSIONS

These findings do not support the morphological-based distinction between Pseudocaligus and Caligus, suggesting that the reduced fourth leg is a feature that has evolved on multiple occasions throughout caligid evolution. Congruent molecular phylogenetic data support groupings based on the presence of morphological features, such as lunules, geography and host fish type rather than appendage morphology. Therefore, we support the synonymy of Pseudocaligus with Caligus.

Omanicotyle heterospina n. gen. et n. comb. (Monogenea: Microcotylidae) from the gills of Argyrops spinifer (Forsskål) (Teleostei: Sparidae) from the Sea of Oman

Background

The Sultanate of Oman’s aquaculture industry is expanding with an on-going assessment of potential new fish species for culture. The king soldier bream, Argyrops spinifer (Forsskål) (Sparidae), is one such species that is under consideration. During a routine health assessment of specimens caught in the Sea of Oman throughout the period November 2009 to March 2011, a number of gill polyopisthocotylean monogeneans were recovered.

Methods

A subsequent study of the monogeneans using a range of morphology-based approaches indicated that these were Bivagina heterospina Mamaev et Parukhin, 1974. In the absence of pre-existing molecular data, an expanded description of this species is provided, including a differential diagnosis with other species and genera belonging to the subfamily Microcotylinae Monticelli, 1892 with the subsequent movement of this species to a new genus to accommodate it.

Results

The polyopisthocotyleans collected from the gills of A. spinifer appear to be unique within the family Microcotylidae Taschenberg, 1879 in that, morphologically, they possess a pair of large, muscular vaginae each armed with a full crown of 16–18 robust spines and a unique dorsal region of folded tegument, which permits their discrimination from species of Bivagina Yamaguti, 1963. Sequencing of the SSU rDNA (complete 1968 bp) and LSU rDNA (partial 949 bp) places the specimens collected during this study within the subfamily Microcotylinae, but the LSU rDNA sequence differs from Bivagina and also from other microcotylid genera. Morphological features of B. heterospina sensu Mamaev et Parukhin, 1974 and the specimens collected from the current study are consistent with one another and represent a single species. The vaginal armature of these worms is unique and differs from all other genera within the Microcotylinae, including Bivagina, and its movement to Omanicotyle n. gen. to accommodate this species is proposed.

Conclusions

A new genus, Omanicotyle n. gen., is erected to accommodate Omanicotyle [Bivagina] heterospina n. comb. which represents the first monogenean to be described from Omani marine waters. Given the pathogenic potential of microcotylids on captive held fish stocks, a full assessment of Omanicotyle heterospina n. gen. et n. comb. is now required before large-scale production commences.

Nucleospora cyclopteri n. sp., an intranuclear microsporidian infecting wild lumpfish, Cyclopterus lumpus L., in Icelandic waters

Background

Commercial fisheries of lumpfish Cyclopterus lumpus have been carried out in Iceland for centuries. Traditionally the most valuable part is the eggs which are harvested for use as a caviar substitute.

Previously reported parasitic infections from lumpfish include an undescribed intranuclear microsporidian associated with abnormal kidneys and mortalities in captive lumpfish in Canada. During Icelandic lumpfish fisheries in spring 2011, extensive enlargements to the kidneys were observed in some fish during processing. The aim of this study was to identify the pathogen responsible for these abnormalities.

Methods

Lumpfish from the Icelandic coast were examined for the causative agent of kidney enlargement. Fish were dissected and used in histological and molecular studies.

Results

Lumpfish, with various grades of clinical signs, were observed at 12 of the 43 sites sampled around Iceland. From a total of 77 fish examined, 18 had clear clinical signs, the most prominent of which was an extensive enlargement and pallor of the kidneys. The histopathology of the most severely affected fish consisted of extensive degeneration and necrosis of kidney tubules and vacuolar degeneration of the haematopoietic tissue. Intranuclear microsporidians were detected in all organs examined in fish with prominent clinical signs and most organs of apparently healthy fish using the new PCR and histological examination. One or multiple uniformly oval shaped spores measuring 3.12 ± 0.15 × 1.30 ± 0.12 μm were observed in the nucleus of affected lymphocytes and lymphocyte precursor cells. DNA sequencing provided a ribosomal DNA sequence that was strongly supported in phylogenetic analyses in a clade containing other microsporidian parasites from the Enterocytozoonidae, showing highest similarity to the intranuclear microsporidian Nucleospora salmonis.

Conclusions

Intranuclear microsporidian infections are common in wild caught lumpfish from around the Icelandic coast. Infections can cause severe clinical signs and extensive histopathological changes, but are also present, at lower levels, in fish that do not show clinical signs. Some common features exist with the intranuclear microsporidian previously reported from captive Canadian lumpfish, but DNA sequence data is required from Canadian fish to confirm conspecificity.

Based on phylogenetic analysis and the intranuclear location of the parasite, the name Nucleospora cyclopteri n. sp. is proposed.

Microsporidia and 'the art of living together'

Parasitism, aptly defined as one of the 'living-together' strategies (Trager, 1986), presents a dynamic system in which the parasite and its host are under evolutionary pressure to evolve new and specific adaptations, thus enabling the coexistence of the two closely interacting partners. Microsporidia are very frequently encountered obligatory intracellular protistan parasites that can infect both animals and some protists and are a consummate example of various aspects of the 'living-together' strategy. Microsporidia, relatives of fungi in the superkingdom Opisthokonta, belong to the relatively small group of parasites for which the host cell cytoplasm is the site of both reproduction and maturation. The structural and physiological reduction of their vegetative stage, together with the manipulation of host cell physiology, enables microsporidia to live in the cytosolic environment for most of their life cycle in a way resembling endocytobionts. The ability to form structurally complex spores and the invention and assembly of a unique injection mechanism enable microsporidia to disperse within host tissues and between host organisms, resulting in long-lasting infections. Microsporidia have adapted their genomes to the intracellular way of life, evolved strategies how to obtain nutrients directly from the host and how to manipulate not only the infected cells, but also the hosts themselves. The enormous variability of host organisms and their tissues provide microsporidian parasites a virtually limitless terrain for diversification and ecological expansion. This review attempts to present a general overview of microsporidia, emphasising some less known and/or more recently discovered facets of their biology.

Spraguea lophii (Microsporidia) parasite of the teleost fish, Lophius piscatorius from Tunisian coasts: evidence for an extensive chromosome length polymorphism

A microsporidian of the genus Spraguea was found parasitizing the nervous tissues of Lophius piscatorius collected from various localities in the Mediterranean coastal areas of Tunisia. The tissue localization, the infection focus aspect and sporal dimorphism are characteristics of Spraguea lophii species. Molecular data based on partial sequence of SSUrRNA encoding gene shows few nucleotide polymorphisms, compared to all described Spraguea isolates. Molecular karyotype obtained on pulsed field gel electrophoresis (1D-PFGE) shows a profile with 14 stained bands in the range of 230-880 kbp and a genome size estimated to 6.700 kbp. The rare cutter endonuclease MluI KARD 2-D-PFGE fingerprint shows an extensive chromosome length polymorphism, but the number of chromosome is unchanged and consists of 15 different molecules. The extensive chromosome length polymorphism is associated to a reduced number of genetic events.

Ultrastructural and molecular studies of Microgemma carolinus n. sp. (Microsporidia), a parasite of the fish Trachinotus carolinus (Carangidae) in Southern Brazil

A new species of Microsporidia Microgemma carolinus n. sp. found in the marine teleost Trachinotus carolinus collected in Florianópolis, Brazil was described based on light, ultrastructural and phylogenetic studies. This parasite developed in the liver forming whitish xenomas that contained different developmental stages with monokaryotic nuclei. The periphery of the xenoma presented some vacuolization and possessed several small projections in the membrane. The mature spores, measuring 3·8 ± 0·4 μm in length and 2·4 ± 0·4 μm in width, were slightly pyriform to ellipsoidal and had rounded ends. The polaroplast was bipartite and the isofilar polar filament was coiled with 8 – 9 turns in a single or double row at the posterior end of the spore. The nucleus was voluminous and in a central position, measuring ∼0·9 μm in diameter. A large posterior vacuole appeared as a pale area, occupying about a third of the spore length. The SSU rRNA gene was sequenced and analysed using maximum parsimony, maximum likelihood and neighbour-joining methods. This study allowed us to conclude that this was a new species of the genus Microgemma, being the first description of this genus from among South America fauna.

Redefining the genus Spraguea based on ultrastructural and phylogenetic data from Spraguea gastrophysus n. sp. (phylum Microsporidia), a parasite found in Lophius gastrophysus (Teleostei) from Brazil

The ultrastructure of the fish-infecting microsporidium Spraguea gastrophysus found in the dorsal ganglia and kidney of the anglerfish, Lophius gastrophysus (family Lophiidae) collected on the Brazilian Atlantic coast is described. Each whitish xenoma (up to 3.1 × 1.8 mm) contains several groups of parasites. The host cells are hypertrophied and contain various parasite life stages including mature spores and several developmental stages with unpaired nuclei. Monomorphic spores are ellipsoidal, lightly curved and measure about 3.35 × 1.71 μm. The spore contains a gradually tapering isofilar polar filament with five to six coils arranged in a single row. The nucleus occupies a central zone of the sporoplasm where also several polyribosomes are presented. The posterior vacuole contains a voluminous spherical and granular posterosome measuring up to ~0.65 μm in diameter. The partial small subunit, intergenic spacer and partial large subunit rRNA gene were sequenced and the phylogenetic analysis places the microsporidian described here in the clade that includes all sequences of the Spraguea genus. The ultrastructural morphology of the xenoma and the spores of this microsporidian parasite, as well as the molecular and phylogenetic analysis, suggest the description of a new species. A redefining of the genus Spraguea is also done.

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 Abraalba (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.

Encephalomyelitis associated with microsporidian infection in farmed greater amberjack, Seriola dumerili (Risso)

An outbreak of a disease characterized by a peculiar spiral movement in farmed greater amberjack, Seriola dumerili (Risso), occurred in Kagoshima Prefecture, Japan, in May 2008, immediately after importing the fish from China. Although neither bacteria nor viruses were detected in routine diagnostic tests, histopathological observations of the affected fish revealed severe inflammation in the tegmentum of the brain including the medulla oblongata and the anterior part of the spinal cord. In addition, a microsporidian parasite was observed in the nerve cell bodies or axons in the inflamed tissues. We identified a microsporidian small subunit rRNA gene (SSU rDNA) from the lesion, and the sequence showed 96.1% identity with that of Spraguea lophii. Subsequent in situ hybridization using probes presumably specific to the SSU rRNA confirmed that the parasite observed in histopathology harboured the identified SSU rRNA. Apparently degenerated microsporidian cells or spores were also frequently observed in tissue sections. Thus, the disease was most probably caused by the infection of a hitherto unknown microsporidian parasite that has a genetic affinity to the genus Spraguea, in the central nervous system of the amberjack.

Spraguea (Microsporida: Spraguidae) infections in the nervous system of the Japanese anglerfish, Lophius litulon (Jordan), with comments on transmission routes and host pathology

Anglerfish from the genus Lophius are a globally important commercial fishery. The microsporidian Spraguea infects the nervous system of these fish resulting in the formation of large, visible parasitic xenomas. Lophius litulon from Japan were investigated to evaluate the intensity and distribution of Spraguea xenomas throughout the nervous system and to assess pathogenicity to the host and possible transmission routes of the parasite. Spraguea infections in L. litulon had a high prevalence; all fish over 403 mm in standard length being infected, with larger fish usually more heavily infected than smaller fish. Seventy percent of all fish examined had some gross visible sign of infection. The initial site of development is the supramedullary cells on the dorsal surface of the medulla oblongata, where all infected fish have parasitic xenomas. As the disease progresses, a number of secondary sites typically become infected such as the spinal, trigeminal and vagus nerves. Fish with infection in the vagus nerve bundles often have simultaneous sites of infection, in particular the spinal nerves and along the ventral nerve towards the urinary bladder. Advanced vagus nerve infections sometimes form xenomas adjacent to kidney tissue. Spraguea DNA was amplified from the contents of the urinary bladders of two fish, suggesting that microsporidian spores may be excreted in the urine. We conclude that supramedullary cells on the hindbrain are the primary site of infection, which is probably initiated at the cutaneous mucous glands where supramedullary cells are known to extend their peripheral axons. The prevalence of Spraguea infections in L. litulon was very high, and infections often extremely heavy; however, no associated pathogenicity was observed, and heavily infected fish were otherwise normal.

Ultrastructural and molecular characterization of a new microsporidium parasite from the Amazonian fish, Gymnorhamphichthys rondoni (Rhamphichthyidae)

A new species of a microsporidium found in the freshwater teleost Gymnorhamphichthys rondoni, collected on the lower Amazon River, is described based on light, ultrastructural, and phylogenetic studies. This parasite develops in the skeletal muscle of the abdominal cavity, forming whitish cyst-like structures containing numerous spores. Mature spores, lightly pyriform to ellipsoidal with rounded ends and measuring 4.25 ± 0.38 × 2.37 ± 0.42 µm (n  =  30), were observed. The spore wall, which measured about 102 nm, was composed of 2 layers with approximately the same thickness. The isofilar polar filament was coiled, with 9-10 (rarely 8) turns. The posterior vacuole appeared as a pale area, occupying about 1/3 of the spore length, and contained a spherical posterosome composed of granular material that was denser at the periphery. The myofibrils located near the spores appeared to be in advanced degradation. Molecular analysis of the rRNA genes, including the ITS region, and phylogenetic analyses using maximum parsimony, maximum likelihood, and Baysesian inference were performed. The ultrastructural characteristics of the spores and the phylogenetic data strongly suggested that it is a new species related to Kabatana, Microgemma, Potaspora, Spraguea, and Tetramicra. We named this new microsporidian from Amazonian fauna as Kabatana rondoni n. sp.

Description and phylogeny of Ceratomyxa anko sp. n. and Zschokkella lophii sp. n. from the Japanese anglerfish, Lophius litulon (Jordan)

Two new species of myxozoans from the Japanese anglerfish, Lophius litulon, are described using myxospore morphology and small subunit rDNA sequences. Ceratomyxa anko sp. n. is a parasite of the gall bladder and had a prevalence of 57%. Mature spores of C. anko sp. n. are arcuate to crescent shaped with valves tapering to rounded tips. A prominent sutural line runs centrally between the round adjacent polar capsules containing the polar filament coiled two to three times. Spore measurements: length 10.8 (9.7-11.9) microm, width 41.9 (36.9-47.2) microm, polar capsule diameter 4.6 (4.1-5.3) microm. Ceratomyxa anko sp. n. can be distinguished from other Ceratomyxa spp. due to its spore dimensions and shape. Zschokkella lophii sp. n. is a parasite of the urinary bladder and had a prevalence of 70%. Mature spores are ellipsoidal to semicircular with bluntly pointed ends. The sutural line is curved or sinuous and the valves have no discernable surface ornamentation. Two almost spherical polar capsules are located separately in the ends of the spore, opening in almost opposite directions and contain the polar filament with five coils. Spore measurements: length 20.1 (16.8-24.0) microm, width 14.9 (12.7-16.8) microm, polar capsule diameter 5.1 (3.6-5.8) microm. Zschokkella lophii sp. n. can be distinguished from other Zschokkella spp. due to the terminal opening of the polar capsules within the spores and the site of infection within the host fish. In the phylogenetic analyses, C. anko sp. n. grouped with other members of the same genus forming a monophyly. Zschokkella lophii sp. n. forms a discrete clade with another Zschokkella sp. that infects the urinary bladder of marine fish. This grouping forms a sister clade to one containing members of the genus Parvicapsula, all of which are parasites of the urinary system in marine fish.

A new microsporidian parasite, Potaspora morhaphis n. gen., n. sp. (Microsporidia) infecting the Teleostean fish, Potamorhaphis guianensis from the River Amazon. Morphological, ultrastructural and molecular characterization

A fish-infecting Microsporidia Potaspora morhaphis n. gen., n. sp. found adherent to the wall of the coelomic cavity of the freshwater fish, Potamorhaphis guianensis, from lower Amazon River is described, based on light microscope and ultrastructural characteristics. This microsporidian forms whitish xenomas distinguished by the numerous filiform and anastomosed microvilli. The xenoma was completely filled by several developmental stages. In all of these stages, the nuclei are monokaryotic and develop in direct contact with host cell cytoplasm. The merogonial plasmodium divides by binary fission and the disporoblastic pyriform spores of sporont origin measure 2·8±0·3×1·5±0·2 μm. In mature spores the polar filament was arranged into 9–10 coils in 2 layers. The polaroplast had 2 distinct regions around the manubrium and an electron-dense globule was observed. The small subunit, intergenic space and partial large subunit rRNA gene were sequenced and maximum parsimony analysis placed the microsporidian described here in the clade that includes the genera Kabatana, Microgemma, Spraguea and Tetramicra. The ultrastructural morphology of the xenoma, and the developmental stages including the spores of this microsporidian parasite, as well as the phylogenetic analysis, suggest the erection of a new genus and species.

Role of the posterior vacuole in Spraguea lophii (Microsporidia) spore hatching

Microsporidia constitute a large group of obligate intracellular protozoan parasites that inject themselves into host cells via the extrusion apparatus of the infective spore stage. Although the injection process is poorly understood, its energy source is thought to reside in the posterior vacuole that swells significantly during spore firing. Here we report the presence and localisation of the key peroxisomal enzymes catalase and acyl-CoA oxidase (ACOX) within the posterior vacuole of Spraguea lophii (Doflein, 1898) spores. Western blot analyses show that these enzymes discharge out of the spore and end up in the medium external to the extruded sporoplasms. The presence of a catalase enzyme system in the Microsporidia was first made evident by the detection of significant levels of molecular oxygen in the medium containing discharging spores in the presence of hydrogen peroxide. Catalase was visualised in inactive, activated, and discharged spores using alkaline diaminobenzidine (DAB) on glutaraldehyde-fixed cells. The position of these enzymes within the extrusion apparatus before and during spore discharge support the Lom and Vávra model that postulates discharge occurs by an eversion process. In addition to these enzymes, spores of S. lophii contain another characteristic peroxisomal component, the very long chain fatty acid (VLCFA) nervonic acid. A sizeable decrease in nervonic acid levels occurs during and after spore discharge. These data indicate that nervonic acid is discharged from the spore into the external medium during firing along with the catalase and ACOX enzymes.

Investigations into microsporidian methionine aminopeptidase type 2: a therapeutic target for microsporidiosis

The Microsporidia have been reported to cause a wide range of clinical diseases particularly in patients that are immunosuppressed. They can infect virtually any organ system and cases of gastrointestinal infection, encephalitis, ocular infection, sinusitis, myositis and disseminated infection are well described in the literature. While benzimidazoles such as albendazole are active against many species of Microsporidia, these drugs do not have significant activity against Enterocytozoon bieneusi. Fumagillin, ovalicin and their analogues have been demonstrated to have antimicrosporidial activity in vitro and in animal models of microsporidiosis. Fumagillin has also been demonstrated to have efficacy in human infections due to E. bieneusi. Fumagillin is an irreversible inhibitor of methionine aminopeptidase type 2 (MetAP2). Homology cloning employing the polymerase chain reaction was used to identify the MetAP2 gene from the human pathogenic microsporidia Encephalitozoon cuniculi, Encephalitozoon hellem, Encephalitozoon intestinalis, Brachiola algerae and E. bieneusi. The full-length MetAP2 coding sequence was obtained for all of the Encephalitozoonidae. Recombinant E. cuniculi MetAP2 was produced in baculovirus and purified using chromatographic techniques. The in vitro activity and effect of the inhibitors bestatin and TNP-470 on this recombinant microsporidian MetAP2 was characterized. An in silico model of E. cuniculi MetAP2 was developed based on crystallographic data on human MetAP2. These reagents provide new tools for the development of in vitro assay systems to screen candidate compounds for use as new therapeutic agents for the treatment of microsporidiosis.