Hepatospora eriocheir (Wang and Chen, 2007) gen. et comb. nov. infecting invasive Chinese mitten crabs (Eriocheir sinensis) in Europe

Ecytonucleospora hepatopenaei n. gen. et comb. (Microsporidia: Enterocytozoonidae): A redescription of the Enterocytozoon hepatopenaei (Tourtip et al., 2009), a microsporidian infecting the widely cultivated shrimp Penaeus vannamei

The microsporidian Enterocytozoon hepatopenaei from Penaeus vannamei (EHPPv) was redescribed on the basis of spore morphology, life cycle, pathology, and molecular character. Compared with the Enterocytozoon hepatopenaei isolated from Penaeus monodon (EHPPm), described by Tourtip et al. in 2009, new features were found in EHPPv. Electron microscopy demonstrated that EHPPv was closely associated with the nucleus of host cell. The merogony and sporogony phages were in direct contact with the cytoplasm of host cells, whereas some of the sporoblasts and the spores were surrounded by the interfacial envelope. Mature spores of EHPPv were oval and monokaryotic, measuring 1.65 ± 0.15 μm × 0.92 ± 0.05 μm. Spores possessed many polyribosomes around a bipartite polaroplast and the polar filament with 4-5 coils in two rows. Phylogenetic analyses showed all Enterocytozoon hepatopenaei isolates shared a common ancestor. Based on the morphological and molecular analyses, we propose the establishment of a new genus Ecytonucleospora and transferring Enterocytozoon hepatopenaei to the genus Ecytonucleospora, retaining the specific epithet hepatopenaei that Tourtip et al. proposed in recognition of their first research, as the new combination Ecytonucleospora hepatopenaei n. comb. Furthermore, it was suggested Enterospora nucleophila, Enterocytozoon sp. isolate RA19015_21, and Enterocytozoon schreckii be assigned into this new genus.

Application of PCR-based diagnostic tools that target Enterocytozoon hepatopenaei for the molecular detection of a Vittaforma-like microsporidium that infects Penaeus vannamei from Costa Rica

Several PCR methodologies are available for the detection of Enterocytozoon hepatopenaei (EHP) that target the SSU rRNA gene. However, these methodologies are reported as unsuitable for the detection of EHP due to specificity issues. Here, we report the applicability of two commonly used SSU rRNA methodologies for the detection of additional microsporidia from the genus Vittaforma that is present in cultured Penaeus vannamei from Costa Rica. The molecular detection of DNA of the novel microsporidia can only be achieved using SSU rRNA targeting methodologies and does not cross-react with the highly specific spore wall protein gene PCR detection method.

Alternosema astaquatica n. sp. (Microsporidia: Enterocytozoonida), a systemic parasite of the crayfish Faxonius virilis

Crayfish have strong ecological impacts in freshwater systems, yet our knowledge of their parasites is limited. This study describes the first systemic microsporidium (infects multiple tissue types) Alternosema astaquatica n. sp. (Enterocytozoonida) isolated from a crayfish host, Faxonius virilis, using histopathology, transmission electron microscopy, gene sequencing, and phylogenetics. The parasite develops in direct contact with the host cell cytoplasm producing mature spores that are monokaryotic and ellipsoid in shape. Spores have 9-10 coils of the polar filament and measure 3.07 ± 0.26 µm (SD) in length and 0.93 ± 0.08 µm (SD) in width. Our novel isolate has high genetic similarity to Alternosema bostrichidis isolated from terrestrial beetles; however, genetic data from this parasite is restricted to a small fragment (396bp) of the SSU gene. Additional data related to spore morphology and development, host, environment, and ecology indicate that our novel isolate is distinct from A. bostrichidis, which supports a new species description. Alternosema astaquatica n. sp. represents a novel member of the Orthosomella-like group which appears to be a set of opportunists within the Enterocytozoonida. The presence of this microsporidium in F. virilis could be relevant for freshwater ecosystems across this crayfish's broad geographic range in North America and may affect interactions between F. virilis and invasive rusty crayfish Faxonius rusticus in the Midwest USA.

Cambaraspora faxoni n. sp. (Microsporidia: Glugeida) from native and invasive crayfish in the USA and a novel host of Cambaraspora floridanus

Crayfishes are among the most widely introduced freshwater taxa and can have extensive ecological impacts. Knowledge of the parasites crayfish harbor is limited, yet co-invasion of parasites is a significant risk associated with invasions. In this study, we describe a novel microsporidium, Cambaraspora faxoni n. sp. (Glugeida: Tuzetiidae), from two crayfish hosts in the Midwest USA, Faxonius virilis and Faxonius rusticus. We also expand the known host range of Cambaraspora floridanus to include Procambarus spiculifer. Cambaraspora faxoni infects muscle and heart tissue of F. rusticus and develops within a sporophorous vesicle. The mature spore measures 3.22 ± 0.14 μm in length and 1.45 ± 0.13 μm in width, with 8-9 turns of the polar filament. SSU sequencing indicates the isolates from F. virilis and F. rusticus were identical (100%) and 93.49% similar to C. floridanus, supporting the erection of a new species within the Cambaraspora genus. The novel parasite was discovered within the native range of F. rusticus (Ohio, USA) and within a native congeneric (F. virilis) in the invasive range of F. rusticus (Wisconsin, USA). Faxonius virilis is invasive in other regions. This new parasite could have been introduced to Wisconsin with F. rusticus or it may be a generalist species with a broad distribution. In either case, this parasite infects two crayfish species that have been widely introduced to new drainages throughout North America and could have future effects on invasion dynamics or impacts.

Pseudohepatospora borealis n. gen. n. sp. (Microsporidia: Enterocytozoonida): A microsporidian pathogen of the Jonah crab (Cancer borealis)

The microsporidian diversity catalogued so far has resulted in the development of several taxonomic groups, one of which is the Enterocytozoonida - a group of generalist 'ultimate opportunists', which infect many fished and aquacultured animals, as well as a broad suite of host taxa, including humans. In this study, we provide phylogenetic, ultrastructural, developmental, and pathological evidence for the creation of a new genus and species to hold a microsporidian parasite of the Jonah crab, Cancer borealis. Cancer borealis represents a species of commercial interest and has become the target of a recently developed fishery on the USA and Canadian Atlantic coast. This species was found to harbour a microsporidian parasite that develops in the cytoplasm of alpha and beta cells of the hepatopancreas. We retrieved a 937 bp fragment of the parasite SSU region, alongside developmental and ultrastructural data that suggests this species is ∼ 87 % similar to Parahepatospora carcini and develops in a similar manner in direct association with the host cell cytoplasm. The mature spores are ovoid in shape and measure 1.48 ± 0.15 µm (SD) in length and 1.00 ± 0.11 µm (SD) in width. Phylogenetically, the new parasite clades in the Enterocytozoonida on the same branch as P. carcini. We provide a new genus and species to hold the parasite: Pseudohepatospora borealis n. gen. n. sp. (Microsporidia: Enterocytozoonida) and explore the likelihood that this species may fit into the Hepatoporidae family.

Using average nucleotide identity (ANI) to evaluate microsporidia species boundaries based on their genetic relatedness

Microsporidia are obligatory intracellular parasites related to fungi and since their discovery their classification and origin has been controversial due to their unique morphology. Early taxonomic studies of microsporidia were based on ultrastructural spore features, characteristics of their life cycle and transmission modes. However, taxonomy and phylogeny based solely on these characteristics can be misleading. SSU rRNA is a traditional marker used in taxonomical classifications, but the power of SSU rRNA to resolve phylogenetic relationships between microsporidia is considered weak at the species level, as it may not show enough variation to distinguish closely related species. Overall genome relatedness indices (OGRI), such as average nucleotide identity (ANI), allows fast and easy-to-implement comparative measurements between genomes to assess species boundaries in prokaryotes, with a 95% cutoff value for grouping genomes of the same species. Due to the increasing availability of complete genomes, metrics of genome relatedness have been applied for eukaryotic microbes taxonomy such as microsporidia. However, the distribution of ANI values and cutoff values for species delimitation have not yet been fully tested in microsporidia. In this study we examined the distribution of ANI values for 65 publicly available microsporidian genomes and tested whether the 95% cutoff value is a good estimation for circumscribing species based on their genetic relatedness.

Full-length transcriptome sequencing and comparative transcriptome analysis of Eriocheir sinensis in response to infection by the microsporidian Hepatospora eriocheir

As a new generation of high-throughput sequencing technology, PacBio Iso-Seq technology (Iso-Seq) provides a better alternative sequencing method for the acquisition of full-length unigenes. In this study, a total of 22.27 gigabyte (Gb) subread bases and 128,614 non-redundant unigenes (mean length: 2,324 bp) were obtained from six main tissues of Eriocheir sinensis including the heart, nerve, intestine, muscle, gills and hepatopancreas. In addition, 74,732 unigenes were mapped to at least one of the following databases: Non-Redundant Protein Sequence Database (NR), Gene Ontology (GO), Kyoto Encyclopaedia of Genes and Genomes (KEGG), KEGG Orthology (KO) and Protein family (Pfam). In addition, 6696 transcription factors (TFs), 28,458 long non-coding RNAs (lncRNAs) and 94,230 mRNA-miRNA pairs were identified. Hepatospora eriocheir is the primary pathogen of E. sinensis and can cause hepatopancreatic necrosis disease (HPND); the intestine is the main target tissue. Here, we attempted to identify the key genes related to H. eriocheir infection in the intestines of E. sinensis. By combining Iso-Seq and Illumina RNA-seq analysis, we identified a total of 12,708 differentially expressed unigenes (DEUs; 6,696 upregulated and 6,012 downregulated) in the crab intestine following infection with H. eriocheir. Based on the biological analysis of these DEUs, several key processes were identified, including energy metabolism-related pathways, cell apoptosis and innate immune-related pathways. Twelve selected genes from these DEUs were subsequently verified by quantitative real-time PCR (qRT-PCR) analysis. Our findings enhance our understanding of the E. sinensis transcriptome and the specific association between E. sinensis and H. eriocheir infection.

Nucleospora hippocampi n. sp., an Intranuclear Microsporidian Infecting the Seahorse Hippocampus erectus From China

The life cycle, ultrastructure, and molecular phylogeny of a new intranuclear microsporidian, Nucleospora hippocampi n. sp., infecting the intestine of the Hippocampus erectus, were described. The histopathology revealed an extensive infection, mainly in the columnar epithelium of the intestinal mucosa layer. The enterocytes were the important target cell for Nucleospora hippocampi n. sp. infection. Transmission electron microscopy results showed that this microsporidian developed directly within the host cell nucleoplasm. In the intranuclear life cycle, the transformation from meront to sporogonial plasmodium was recognized by forming electron-dense disc structures, which were considered the polar tube precursors. The microsporidian showed the typical morphological characteristics of the family Enterocytozoonidae in the formation and development of spore organelles prior to the division of the sporogonial plasmodium. According to wet smear observation, eight spores were generally formed in a single host nucleus. Mature spores were elongated ovoids that were slightly bent and measured 1.93 × 0.97 μm. The isofilar polar tube was arranged in 7~8 coils in one row. Phylogenetic analysis of its small subunit ribosomal DNA sequences demonstrated that the parasite belonged to the Nucleospora group clade. The histological, ultrastructural, and molecular data support the emergence of a new species in the genus Nucleospora. This is the first report of Nucleospora species in Asia and threatened syngnathid fishes.

Assessing the potential for invasive species introductions and secondary spread using vessel movements in maritime ports

Global shipping facilitates the introduction of invasive species and parasites via ballast water and hull fouling. Regional management of invasives may be strengthened by identifying the major routes in a network, to allow for targeted ship inspections. This study used cargo shipping records to establish the connectivity of shipping routes between ports in Ireland and other nations. 9291 records were analysed, investigating vessel residence and journey times. On average, vessels spent up to five days in port and less than five days at sea. However, there was strong variation, with general cargo ships recording up to 13 days in port. A horizon scan for species likely to invade in Ireland was incorporated for five species and their associated parasites: American razor clam, Asian shore crab, Brush clawed shore crab, Chinese mitten crab and American slipper limpet. Routes of concern are highlighted and a general framework for effective management is outlined.

Microsporidian Pathogens of Aquatic Animals

Around 57.1% of microsporidia occupy aquatic environments, excluding a further 25.7% that utilise both terrestrial and aquatic systems. The aquatic microsporidia therefore compose the most diverse elements of the Microsporidia phylum, boasting unique structural features, variable transmission pathways, and significant ecological influence. From deep oceans to tropical rivers, these parasites are present in most aquatic environments and have been shown to infect hosts from across the Protozoa and Animalia. The consequences of infection range from mortality to intricate behavioural change, and their presence in aquatic communities often alters the overall functioning of the ecosystem.In this chapter, we explore aquatic microsporidian diversity from the perspective of aquatic animal health. Examples of microsporidian parasitism of importance to an aquacultural ('One Health') context and ecosystem context are focussed upon. These include infection of commercially important penaeid shrimp by Enterocytozoon hepatopenaei and interesting hyperparasitic microsporidians of wild host groups.Out of ~1500 suggested microsporidian species, 202 have been adequately taxonomically described using a combination of ultrastructural and genetic techniques from aquatic and semi-aquatic hosts. These species are our primary focus, and we suggest that the remaining diversity have additional genetic or morphological data collected to formalise their underlying systematics.

Panopeispora mellora n. gen. n. sp. (microsporidia) infecting Say's crab (Dyspanopeus sayi) from the Atlantic shoreline of Canada

Say's mud crab, Dyspanopeus sayi (Brachyura: Panopeidae) is a native shallow subtidal and inter-tidal inhabitant of the Atlantic coastline of North America and an invasive species in the Mediterranean and Black Seas. Little is known about the microparasites of this host and the broader Panopeidae. We describe a novel microsporidian parasite infecting the musculature of D. sayi from Malagash, Nova Scotia (Canada), at a prevalence of 7%. Histopathology and molecular diagnostics were used to describe pathology and parasite phylogenetics, respectively. Based on SSU rDNA gene sequencing we propose that the microsporidian requires establishment of a new genus (Panopeispora n. gen.) and species (Panopeispora mellora n. sp.), due to significant differences to closest known taxa (e.g. Facilispora margolisi [81% similarity] and Thelohania butleri [80% similarity]), residing in Clade V of the Microsporidia. Archived, wax-embedded histological material was re-processed for transmission electron microscopy to obtain preliminary details of its intracellular development cycle and ultrastructure within the host musculature. The discovery of this pathogen is discussed with relevance to microsporidian taxonomy and the potential for achieving ultrastructural data from archived material.

Occurrence of Enterocytozoon hepatopenaei (EHP) infection on Penaeus vannamei in one rearing cycle

The microsporidian parasite Enterocytozoon hepatopenaei (EHP) is an emerging problem in the marine shrimp industry, primarily in Asian countries such as China, Thailand, India, Malaysia, Indonesia, and Vietnam. A screening was conducted to investigate the prevalence of EHP after a fixed period of culturing for 1 rearing cycle in 3 states of Malaysia. The screening stages covered Penaeus vannamei post larvae (PL) and after 14-30, 31-50, 51-70, and 71-90 d of culture in 1 production cycle. A total of 279 samples were amplified using a PCR assay targeting the gene encoding a spore wall protein (SWP) of EHP. The EHP infection was initially detected in the hatchery and increased to 96.6% after the shrimp were transferred to the pond. The positive EHP sequence showed 91 to 100% similarity to sequences from India, Thailand, Vietnam, Indonesia, and Latin America. EHP infection increased throughout 1 rearing cycle due to factors such as the cannibalistic feeding habits of shrimp and the presence of unknown vectors or carriers of EHP in the culture ponds. Hence, the finding from the current study will be fundamental for other studies concerning EHP.

Isolation of the Parasite Enterocytospora artemiae From Chinese Grass Shrimp (Palaemonetes sinensis)-First Report in Asia

Chinese grass shrimp (Palaemonetes sinensis) is an economically important crustacean in Chinese aquaculture. Recently, we found that shrimp in Panjin city were infected with microsporidia, a group of fungi. The hepatopancreas of several infected shrimp showed white turbidity and pathological changes that negatively affected the health and appearance of the shrimp. Histopathology and transmission electron microscopy were used to examine the development of the parasite within its parasitophorous vacuole. Our results indicated that microsporidia developed asynchronously within the same parasitophorous vacuole. The spores were predominantly small, and rod or oval-shaped. The sizes of fresh spores were approximately 3.1 × 2.4 μm and fixed spores were 1.9 × 1.1 μm. The polar filament was isofilar with 5-6 coils and the thickness was 103.2 nm. Merogonial divisions occurred by binary fission and sporogonial division occurred by plasmotomy. The small subunit ribosomal DNA sequence (1295 bp) from the parasite was highly similar to the previously reported parasite Enterocytospora artemiae (99% nucleotide identity, JX915760). Using maximum likelihood to analyze the phylogenetic relationships, we found that this microsporidian should be grouped within Clade IV, an Enterocytospora-like clade, of the Microsporidia phylum. Based on this parasite's life cycle characteristics, morphology, and small subunit ribosomal DNA sequence, the parasite described here is likely E. artemiae, which has previously only been described in Europe and North America. Thus, this is the first report of E. artemiae both in Asia and economically important shrimp.

Mechanisms of possible self-limitation in the invasive Asian shore crab Hemigrapsus sanguineus

Population sizes of invasive species are commonly characterized by boom-bust dynamics, and self-limitation via resource depletion is posited as one factor leading to these boom-bust changes in population size. Yet, while this phenomenon is well-documented in plants, few studies have demonstrated that self-limitation is possible for invasive animal species, especially those that are mobile. Here we examined the invasive Asian shore crab Hemigrapsus sanguineus, a species that reached very high abundances throughout invaded regions of North America, but has recently declined in many of these same regions. We examined the relationship between diet, energy storage, reproduction, and growth in crabs collected from the New Hampshire coast. We show that energy storage and reproduction both increase with diet quality, while growth declines with diet quality. These results suggest that self-limitation may be a contributing factor to the recent declines of H. sanguineus at sites where this invader was once much more abundant. Further, these results suggest a diet-associated tradeoff in energy allocation to different vital rates, with a focus on reproduction when high quality resources are consumed, and a focus instead on growth when poor quality resources are consumed.

The shrimp microsporidian Enterocytozoon hepatopenaei (EHP): Biology, pathology, diagnostics and control

Disease is a major limiting factor in the global production of cultivated shrimp. The microsporidian parasite Enterocytozoon hepatopenaei (EHP) was formally characterized in 2009 as a rare infection of the black tiger shrimp Penaeus monodon. It remained relatively unstudied until mid-2010, after which infection with EHP became increasingly common in the Pacific whiteleg shrimp Penaeus vannamei, by then the most common shrimp species farmed in Asia. EHP infects the hepatopancreas of its host, causing hepatopancreatic microsporidiosis (HPM), a condition that has been associated with slow growth of the host in aquaculture settings. Unlike other infectious disease agents that have caused economic losses in global shrimp aquaculture, EHP has proven more challenging because too little is still known about its environmental reservoirs and modes of transmission during the industrial shrimp production process. This review summarizes our current knowledge of the EHP life cycle and the molecular strategies that it employs as an obligate intracellular parasite. It also provides an analysis of available and new methodologies for diagnosis since most of the current literature on EHP focuses on that topic. We summarize current knowledge of EHP infection and transmission dynamics and currently recommended, practical control measures that are being applied to limit its negative impact on shrimp cultivation. We also point out the major gaps in knowledge that urgently need to be bridged in order to improve control measures.

Cytopathology and immune response in the hepatopancreas of decapod crustaceans

The hepatopancreas of decapod crustaceans is used as an example to illustrate the range of cytopathologies, detoxification mechanisms, and immune responses that environmental toxicants and pathogens can induce in a single organ. The hepatopancreas is the central metabolic organ of decapods and consists of hundreds of blindly-ending tubules and intertubular spaces. The tubular epithelium contains 5 structurally and functionally different cell types, and the interstitium contains haemolymph, haemocytes, connective tissue, and fixed phagocytes. Some physiological conditions such as moulting and starvation cause marked but reversible ultrastructural alterations of the epithelial cells. Environmental toxicants induce either detoxification mechanisms or structural damage in cells, depending on toxicant and concentration. The hepatopancreas is also a main target organ for pathogens, mainly viruses, bacteria, and protists that enter the body via the digestive tract and gills and replicate in the hepatopancreatocytes. The cytopathologies caused by toxicants and pathogens affect single cell types specifically or, more often, several cell types simultaneously. Pathogenesis often begins in a certain cell organelle such as the nucleus, mitochondrion, or endoplasmic reticulum, spreads to other organelles, and ends with death of the infected cell. Fixed phagocytes in the interstitium capture and degrade pathogens that move from the infected tubules into the intertubular spaces or enter the hepatopancreas via circulation. Relatively few disease agents elicit the melanisation and encapsulation reaction that encloses infected tubules by a rigid melanised capsule and kills the entrapped pathogens.

An integrated metabolic consequence of Hepatospora eriocheir infection in the Chinese mitten crab Eriocheir sinensis

Despite the economic and evolutionary importance of aquatic host-infecting microsporidian species, at present, limited information has been provided about the microsporidia-host interactions. This study focused on Hepatospora eriocheir, an emerging microsporidian pathogen for the Chinese mitten crab Eriocheir sinensis. Hypertrophy of hepatopancreas cells was a common feature of H. eriocheir infection. More importantly, mitochondria of the hepatopancreas were drawn around the H. eriocheir, most likely to aid the uptake of ATP directly from the host. To better understand the crab anti-microsporidian response, de novo transcriptome sequencing of the hepatopancreas tissue was furtherly proceeded. A total of 47.84 M and 57.21 M clean reads were generated from the hepatopancreas of H. eriocheir infected and control groups respectively. Based on homology searches, functional annotation with 6 databases (Nr, Swiss-Prot, KEGG, KOGs, Pfam and GO) for 88,168 unigenes was performed. 2619 genes were identified as differently up-regulated and 2541 genes as differently down-regulated. Prominent functional categories enriched with differentially expressed genes (DEGs) were "ATP binding", "mitochondrion and extracellular region", "oxygen transporter activity", "oxidoreductase activity", "alanine, aspartate and glutamate metabolism", "carbohydrate metabolic process", "starch and sucrose metabolism" and "fatty acid biosynthesis". These results confirmed a parasite external energy supply and an integrated metabolic stress. In addition, simple sequence repeats (SSRs) and single nucleotide polymorphisms (SNPs) were also identified from the gene library. Taken together, these findings allow us to better understand the underlying mechanisms regulating interactions between H. eriocheir and the crab E. sinensis.

Development of In situ hybridization and real-time PCR assays for the detection of Hepatospora eriocheir, a microsporidian pathogen in the Chinese mitten crab Eriocheir sinensis

A microsporidian parasite, Hepatospora eriocheir, is an emerging pathogen for the Chinese mitten crab Eriocheir sinensis. Currently, there is scant information about the way it transmits infection in the crustacean of commercial importance, including its pathogenesis, propagation and infection route in vivo. In this study, chromogenic in situ hybridization (ISH) and quantitative real-time PCR (qPCR) assays were developed to address this pressing need, and we provided an advance in the detection methods available. Pathogens can be seen in situ with associated lesions using ISH. Positive hybridization signals were noted inside the epithelial cells of the hepatopancreas, and putative free parasite spores were observed within the tubule lumen, which were associated with lesions detected by electron microscopy and haematoxylin and eosin (H&E) analysis. qPCR allows the determination of parasite loads in infected tissues, which is important for understanding disease progression and transmission. The hepatopancreas displayed the biggest statistical copy numbers among different tissues of infected crabs, confirming a tissue-specific pathogen infection characteristic. The qPCR assay also proved to be suitable for the diagnosis of asymptomatic carrier crabs. Combination of the two methods could facilitate the study of H. eriocheir infection mechanism in E. sinensis, enhance the early diagnosis of the pathogen and improve the management of microsporidian diseases in commercial crustaceans.

Parasites, pathogens and commensals in the "low-impact" non-native amphipod host Gammarus roeselii

Background

Whilst vastly understudied, pathogens of non-native species (NNS) are increasingly recognised as important threats to native wildlife. This study builds upon recent recommendations for improved screening for pathogens in NNS by focusing on populations of Gammarus roeselii in Chojna, north-western Poland. At this location, and in other parts of continental Europe, G. roeselii is considered a well-established and relatively ‘low-impact’ invader, with little understanding about its underlying pathogen profile and even less on potential spill-over of these pathogens to native species.

Results

Using a combination of histological, ultrastructural and phylogenetic approaches, we define a pathogen profile for non-native populations of G. roeselii in Poland. This profile comprised acanthocephalans (Polymorphus minutus Goese, 1782 and Pomphorhynchus sp.), digenean trematodes, commensal rotifers, commensal and parasitic ciliated protists, gregarines, microsporidia, a putative rickettsia-like organism, filamentous bacteria and two viral pathogens, the majority of which are previously unknown to science. To demonstrate potential for such pathogenic risks to be characterised from a taxonomic perspective, one of the pathogens, a novel microsporidian, is described based upon its pathology, developmental cycle and SSU rRNA gene phylogeny. The novel microsporidian Cucumispora roeselii n. sp. displayed closest morphological and phylogenetic similarity to two previously described taxa, Cucumispora dikerogammari (Ovcharenko & Kurandina, 1987), and Cucumispora ornata Bojko, Dunn, Stebbing, Ross, Kerr & Stentiford, 2015.

Conclusions

In addition to our discovery extending the host range for the genus Cucumispora Ovcharenko, Bacela, Wilkinson, Ironside, Rigaud & Wattier, 2010 outside of the amphipod host genus Dikerogammarus Stebbing, we reveal significant potential for the co-transfer of (previously unknown) pathogens alongside this host when invading novel locations. This study highlights the importance of pre-invasion screening of low-impact NNS and, provides a means to document and potentially mitigate the additional risks posed by previously unknown pathogens.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2108-6) contains supplementary material, which is available to authorized users.

Parahepatospora carcini n. gen., n. sp., a parasite of invasive Carcinus maenas with intermediate features of sporogony between the Enterocytozoon clade and other microsporidia

Parahepatospora carcini n. gen. n. sp., is a novel microsporidian parasite discovered infecting the cytoplasm of epithelial cells of the hepatopancreas of a single Carcinus maenas specimen. The crab was sampled from within its invasive range in Atlantic Canada (Nova Scotia). Histopathology and transmission electron microscopy were used to show the development of the parasite within a simple interfacial membrane, culminating in the formation of unikaryotic spores with 5-6 turns of an isofilar polar filament. Formation of a multinucleate meront (>12 nuclei observed) preceded thickening and invagination of the plasmodial membrane, and in many cases, formation of spore extrusion precursors (polar filaments, anchoring disk) prior to complete separation of pre-sporoblasts from the sporogonial plasmodium. This developmental feature is intermediate between the Enterocytozoonidae (formation of spore extrusion precursors within the sporont plasmodium) and all other Microsporidia (formation of spore extrusion precursors after separation of sporont from the sporont plasmodium). SSU rRNA-based gene phylogenies place P. carcini within microsporidian Clade IV, between the Enterocytozoonidae and the so-called Enterocytospora-clade, which includes Enterocytospora artemiae and Globulispora mitoportans. Both of these groups contain gut-infecting microsporidians of aquatic invertebrates, fish and humans. According to morphological and phylogenetic characters, we propose that P. carcini occupies a basal position to the Enterocytozoonidae. We discuss the discovery of this parasite from a taxonomic perspective and consider its origins and presence within a high profile invasive host on the Atlantic Canadian coastline.

Hyperspora aquatica n.gn., n.sp. (Microsporidia), hyperparasitic in Marteilia cochillia (Paramyxida), is closely related to crustacean-infecting microspordian taxa

The Paramyxida, closely related to haplosporidians, paradinids, and mikrocytids, is an obscure order of parasitic protists within the class Ascetosporea. All characterized ascetosporeans are parasites of invertebrate hosts, including molluscs, crustaceans and polychaetes. Representatives of the genus Marteilia are the best studied paramyxids, largely due to their impact on cultured oyster stocks, and their listing in international legislative frameworks. Although several examples of microsporidian hyperparasitism of paramyxids have been reported, phylogenetic data for these taxa are lacking. Recently, a microsporidian parasite was described infecting the paramyxid Marteilia cochillia, a serious pathogen of European cockles. In the current study, we investigated the phylogeny of the microsporidian hyperparasite infecting M. cochillia in cockles and, a further hyperparasite, Unikaryon legeri infecting the digenean Meiogymnophallus minutus, also in cockles. We show that rather than representing basally branching taxa in the increasingly replete Cryptomycota/Rozellomycota outgroup (containing taxa such as Mitosporidium and Paramicrosoridium), these hyperparasites instead group with other known microsporidian parasites infecting aquatic crustaceans. In doing so, we erect a new genus and species (Hyperspora aquatica n. gn., n.sp.) to contain the hyperparasite of M. cochillia and clarify the phylogenetic position of U. legeri. We propose that in both cases, hyperparasitism may provide a strategy for the vectoring of microsporidians between hosts of different trophic status (e.g. molluscs to crustaceans) within aquatic systems. In particular, we propose that the paramyxid hyperparasite H. aquatica may eventually be detected as a parasite of marine crustaceans. The potential route of transmission of the microsporidian between the paramyxid (in its host cockle) to crustaceans, and, the 'hitch-hiking' strategy employed by H. aquatica is discussed.

First case of hepatopancreatic necrosis disease in pond-reared Chinese mitten crab, Eriocheir sinensis, associated with microsporidian

An epidemic of hepatopancreatic necrosis disease (HPND) with a high mortality rate (40%-50%) recently occurred in the cultured Chinese mitten crab, Eriocheir sinensis, which is a very important economic crustacean species in China. Histology revealed infection by a microsporidian parasite within the cytoplasm of the epithelial cells of the hepatopancreas. Numerous discrete inclusions in the infected cells and presumably free parasite spores were also observed. By negative staining using electron microscopy, a typical morphology of spores was observed with a protuberant front of the anchoring disc. Infection was confined to the epithelial cells of the hepatopancreas, with no other organ implicated. By sequencing the PCR products using specific primers based on conserved regions of microsporidian small subunit (18S) ribosomal DNA, it was revealed that the parasite from HPND ponds had 99% sequence identity to that of Hepatospora eriocheir. Phylogentic analysis also placed the microsporidian in the same lineage as H. eriocheir. This study reported the first case of widespread infections of H. eriocheir associated with HPND found in the pond-reared Chinese mitten crab, E. sinensis. The description of microsporidian in this important commercial host is fundamental for future consideration of factors affecting stock health and sustainability.

Microsporidia - Emergent Pathogens in the Global Food Chain

Intensification of food production has the potential to drive increased disease prevalence in food plants and animals. Microsporidia are diversely distributed, opportunistic, and density-dependent parasites infecting hosts from almost all known animal taxa. They are frequent in highly managed aquatic and terrestrial hosts, many of which are vulnerable to epizootics, and all of which are crucial for the stability of the animal-human food chain. Mass rearing and changes in global climate may exacerbate disease and more efficient transmission of parasites in stressed or immune-deficient hosts. Further, human microsporidiosis appears to be adventitious and primarily associated with an increasing community of immune-deficient individuals. Taken together, strong evidence exists for an increasing prevalence of microsporidiosis in animals and humans, and for sharing of pathogens across hosts and biomes.

Single and multi-gene phylogeny of Hepatospora (Microsporidia) - a generalist pathogen of farmed and wild crustacean hosts

Almost half of all known microsporidian taxa infect aquatic animals. Of these, many cause disease in arthropods. Hepatospora, a recently erected genus, infects epithelial cells of the hepatopancreas of wild and farmed decapod crustaceans. We isolated Hepatospora spp. from three different crustacean hosts, inhabiting different habitats and niches; marine edible crab (Cancer pagurus), estuarine and freshwater Chinese mitten crab (Eriocheir sinensis) and the marine mussel symbiont pea crab (Pinnotheres pisum). Isolates were initially compared using histology and electron microscopy revealing variation in size, polar filament arrangement and nuclear development. However, sequence analysis of the partial SSU rDNA gene could not distinguish between the isolates (~99% similarity). In an attempt to resolve the relationship between Hepatospora isolated from E. sinensis and C. pagurus, six additional gene sequences were mined from on-going unpublished genome projects (RNA polymerase, arginyl tRNA synthetase, prolyl tRNA synthetase, chitin synthase, beta tubulin and heat shock protein 70). Primers were designed based on the above gene sequences to analyse Hepatospora isolated from pea crab. Despite application of gene sequences to concatenated phylogenies, we were unable to discriminate Hepatospora isolates obtained from these hosts and concluded that they likely represent a single species or, at least subspecies thereof. In this instance, concatenated phylogenetic analysis supported the SSU-based phylogeny, and further, demonstrated that microsporidian taxonomies based upon morphology alone are unreliable, even at the level of the species. Our data, together with description of H. eriocheir in Asian crab farms, reveal a preponderance for microvariants of this parasite to infect the gut of a wide array of decapods crustacean hosts and the potential for Hepatospora to exist as a cline across wide geographies and habitats.

Biology of a new xenoma-forming gonadotropic microsporidium in the invasive blotchfin dragonet Callionymus filamentosus

A gonadotropic microsporidian parasite, Obruspora papernae gen. et sp. nov. (Microsporidia: Enterocytozoonidae), is described from Callionymus filamentosus (Teleostei: Callionymidae) in the Mediterranean Sea. The host, a Red Sea invasive species which entered the Mediterranean through the Suez Canal, was first collected in the Levant Basin in 1953, whereas its parasite went unobserved until 2008. Analysis of partial small subunit ribosomal gene sequences (SSU rDNA) placed the new species within the Nucleospora, Desmozoon, and Paranucleospora clade, and as it differs from each of them, it is assigned to a new genus. The development of the parasite is described, and the biological mechanisms underlying this parasite-host system are analyzed. Prevalence of infection approached 80% in female samples throughout most of the year. Males showed no signs of infection, but parasite rDNA was detected in male internal organs. The parasite-induced xenomas progressively occupied and eventually replaced much of the ovary, in some cases producing effective castration. Despite high levels of parasite infection, current trawl fishery statistics indicate that the abundance of Mediterranean populations of the host remains high. The parasite impact on the host population dynamics is unclear. Possible effects of the new microsporidian parasite on the reproductive effort of C. filamentosus and the potential role of another parasite, the ectoparasitic copepod Lernanthropus callionymicola, as an additional host in the life cycle of O. papernae, require further investigation.

Areospora rohanae n.gen. n.sp. (Microsporidia; Areosporiidae n. fam.) elicits multi-nucleate giant-cell formation in southern king crab (Lithodes santolla)

This paper utilises histological, ultrastructure and molecular phylogenetic data to describe a novel genus and species (Areospora rohanae n.gen., n.sp.) within the phylum Microsporidia. Phylogenetic and morphological distinction from other known lineages within the phylum also provide strong support for erection of a new family (Areosporiidae n. fam) to contain the parasite. Recognised via lesions observed by workers in king crab processing facilities in southern Chile, the parasite elicits giant cell formation in infected crabs. Merogony within haemocytes and fixed phagocytes proceeds apparent fusion of infected cells to produce multinucleate syncitia in which further development of the parasite occurs. Subsequent recruitment of adjacent cells within the haemal spaces of the hepatopancreas, the podocytes of the gill, and particularly in the subcuticular connective tissues, characterises the pathogenesis of A. rohanae. In late stages of infection, significant remodelling of the subcuticular tissues corresponds to the clinical lesions observed within processing plants. Sporogony of A. rohanae also occurs within the syncitial cytoplasm and culminates in production of bizarre spores, ornamented with distinctive tubular bristles. Spores occur in sets of 8 within a sporophorous vesicle. The description of A. rohanae offers considerable insight into the pathogenesis of giant-cell forming Microsporidia, signifies a new lineage of giant-cell forming Microsporidia in marine hosts, and may reflect emergence of a commercially-significant pathogen in the southern ocean Lithodes santolla fishery.

Baseline histopathological survey of a recently invading island population of 'killer shrimp', Dikerogammarus villosus

Dikerogammarus villosus, an invasive amphipod, has recently been detected in UK freshwaters. To assess the potential for pathogen introduction with the invader, a year-long histopathology survey of the D. villosus population inhabiting the initial site of detection (Grafham Water, Cambridgeshire, UK) was conducted. Additional samples were collected from 2 other subsequently identified populations within the UK (Cardiff Bay and Norfolk Broads), and from established populations in France (River Rhine) and Poland (River Vistula). The data revealed a range of pathogens and commensals. Several pathogens occurring within continental populations were not present within the UK populations. Microsporidian parasites and a novel viral pathogen were amongst those not observed in the UK. The absence of these pathogens at UK sites may therefore impart significant survival advantages to D. villosus over native fauna, thereby increasing its success as an invader. The contrast in pathogen profile between UK and continental-invasive populations of D. villosus provides preliminary evidence for so-called 'enemy release' in UK populations of D. villosus and is suggestive of single-point introductions, rather than continual incursion events as previously observed throughout its continental invasive range. This baseline survey provides important data on the pathogen and commensal profile of a high-impact, invasive species early in its invasion history of the UK. It can be utilised to assess potential for temporal pathogen acquisition by non-native invasive aquatic species and to investigate competitive advantages placed upon this invader due to absence of important pathogens experienced within its native range.

Cytological, molecular and life cycle characterization of Anostracospora rigaudi n. g., n. sp. and Enterocytospora artemiae n. g., n. sp., two new microsporidian parasites infecting gut tissues of the brine shrimp Artemia

Two new microsporidia, Anostracospora rigaudi n. g., n. sp., and Enterocytospora artemiae n. g., n. sp. infecting the intestinal epithelium of Artemia parthenogenetica Bowen and Sterling, 1978 and Artemia franciscana Kellogg, 1906 in southern France are described. Molecular analyses revealed the two species belong to a clade of microsporidian parasites that preferentially infect the intestinal epithelium of insect and crustacean hosts. These parasites are morphologically distinguishable from other gut microsporidia infecting Artemia. All life cycle stages have isolated nuclei. Fixed spores measure 1·3×0·7 μm with 5-6 polar tube coils for A. rigaudi and 1·2×0·9 μm with 4 polar tube coils for E. artemiae. Transmission of both species is horizontal, most likely through the ingestion of spores released with the faeces of infected hosts. The minute size of these species, together with their intestinal localization, makes their detection and identification difficult. We developed two species-specific molecular markers allowing each type of infection to be detected within 3-6 days post-inoculation. Using these markers, we show that the prevalence of these microsporidia ranges from 20% to 75% in natural populations. Hence, this study illustrates the usefulness of molecular approaches to study prevalent, but cryptic, infections involving microsporidian parasites of gut tissues.

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.

A new microsporidium, Triwangia caridinae gen. nov., sp. nov. parasitizing fresh water shrimp, Caridina formosae (Decapoda: Atyidae) in Taiwan

A new microsporidium was isolated from the endemic, Taiwanese shrimp, Caridina formosae (Decapoda, Atyidae) from northern Taiwan. A conspicuous symptom of infection was presence of opaque white xenomas located in the proximity of the alimentary tract, the surface of the hepatopancreas, and the gills. A fully developed xenoma consisted of a hard, thick capsule filled with sporophorous vesicles containing multiple spores. Microsporidia developed synchronously within the same sporophorous vesicle, although the stage of parasite development differed among the vesicles. Fresh spores were pyriform, mononucleated and measured 6.53 × 4.38 μm. The polar filament was anisofilar with 9-11 coils. Phylogenetic analysis based on the small subunit ribosomal DNA sequence showed that the isolate is most similar to the fish microsporidian clade containing the genera Kabatana, Microgemma, Potaspora, Spraguea, and Teramicra. The highest sequence identity, 80%, was with Spraguea spp. Based on pathogenesis, life cycle and phylogenetic analysis, we erect a new genus and species, Triwangia caridinae for the novel microsporidium.

Disease will limit future food supply from the global crustacean fishery and aquaculture sectors

Seafood is a highly traded food commodity. Farmed and captured crustaceans contribute a significant proportion with annual production exceeding 10 M metric tonnes with first sale value of $40bn. The sector is dominated by farmed tropical marine shrimp, the fastest growing sector of the global aquaculture industry. It is significant in supporting rural livelihoods and alleviating poverty in producing nations within Asia and Latin America while forming an increasing contribution to aquatic food supply in more developed countries. Nations with marine borders often also support important marine fisheries for crustaceans that are regionally traded as live animals and commodity products. A general separation of net producing and net consuming nations for crustacean seafood has created a truly globalised food industry. Projections for increasing global demand for seafood in the face of level or declining fisheries requires continued expansion and intensification of aquaculture while ensuring best utilisation of captured stocks. Furthermore, continued pressure from consuming nations to ensure safe products for human consumption are being augmented by additional legislative requirements for animals (and their products) to be of low disease status. As a consequence, increasing emphasis is being placed on enforcement of regulations and better governance of the sector; currently this is a challenge in light of a fragmented industry and less stringent regulations associated with animal disease within producer nations. Current estimates predict that up to 40% of tropical shrimp production (>$3bn) is lost annually, mainly due to viral pathogens for which standard preventative measures (e.g. such as vaccination) are not feasible. In light of this problem, new approaches are urgently required to enhance yield by improving broodstock and larval sourcing, promoting best management practices by farmer outreach and supporting cutting-edge research that aims to harness the natural abilities of invertebrates to mitigate assault from pathogens (e.g. the use of RNA interference therapeutics). In terms of fisheries losses associated with disease, key issues are centred on mortality and quality degradation in the post-capture phase, largely due to poor grading and handling by fishers and the industry chain. Occurrence of disease in wild crustaceans is also widely reported, with some indications that climatic changes may be increasing susceptibility to important pathogens (e.g. the parasite Hematodinium). However, despite improvements in field and laboratory diagnostics, defining population-level effects of disease in these fisheries remains elusive. Coordination of disease specialists with fisheries scientists will be required to understand current and future impacts of existing and emergent diseases on wild stocks. Overall, the increasing demand for crustacean seafood in light of these issues signals a clear warning for the future sustainability of this global industry. The linking together of global experts in the culture, capture and trading of crustaceans with pathologists, epidemiologists, ecologists, therapeutics specialists and policy makers in the field of food security will allow these issues to be better identified and addressed.