A new intranuclear microsporidium, Enterospora nucleophila n. sp., causing an emaciative syndrome in a piscine host (Sparus aurata), prompts the redescription of the family Enterocytozoonidae

Establishment of a TaqMan probe-based qPCR assay for detecting microsporidia Enterospora epinepheli in grouper

Enterospora epinepheli is an intranuclear microsporidian parasite causing serious emaciative disease in hatchery-bred juvenile groupers (Epinephelus spp.). Rapid and sensitive detection is urgently needed as its chronic infection tends to cause emaciation as well as white faeces syndrome and results in fry mortality. This study established a TaqMan probe-based real-time quantitative PCR assays targeting the small subunit rRNA (SSU) gene of E. epinepheli. The relationship between the standard curve of cycle threshold (Ct) and the logarithmic starting quantity (SQ) was determined as Ct = -3.177 lg (SQ) + 38.397. The correlation coefficient (R2 ) was 0.999, and the amplification efficiency was 106.4%. The detection limit of the TaqMan probe-based qPCR assay was 1.0 × 101 copies/μL and that is 100 times sensitive than the traditional PCR method. There is no cross-reaction with other aquatic microsporidia such as Ecytonucleospora hepatopenaei, Nucleospora hippocampi, Potaspora sp., Ameson portunus. The intra-assay and inter-assay showed great repeatability and reproducibility. In addition, the test of clinical samples showed that this assay effectively detected E. epinepheli in the grouper's intestine tissue. The established TaqMan qPCR assays will be a valuable diagnostic tool for the epidemiological investigation as well as prevention and control of E. epinepheli.

Ultrastructural insights into the microsporidian infection apparatus reveal the kinetics and morphological transitions of polar tube and cargo during host cell invasion

During host cell invasion, microsporidian spores translocate their entire cytoplasmic content through a thin, hollow superstructure known as the polar tube. To achieve this, the polar tube transitions from a compact spring-like state inside the environmental spore to a long needle-like tube capable of long-range sporoplasm delivery. The unique mechanical properties of the building blocks of the polar tube allow for an explosive transition from compact to extended state and support the rapid cargo translocation process. The molecular and structural factors enabling this ultrafast process and the structural changes during cargo delivery are unknown. Here, we employ light microscopy and in situ cryo-electron tomography to visualize multiple ultrastructural states of the Vairimorpha necatrix polar tube, allowing us to evaluate the kinetics of its germination and characterize the underlying morphological transitions. We describe a cargo-filled state with a unique ordered arrangement of microsporidian ribosomes, which cluster along the thin tube wall, and an empty post-translocation state with a reduced diameter but a thicker wall. Together with a proteomic analysis of endogenously affinity-purified polar tubes, our work provides comprehensive data on the infection apparatus of microsporidia and uncovers new aspects of ribosome regulation and transport.

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.

Microsporidia in Commercially Harvested Marine Fish: A Potential Health Risk for Consumers

Microsporidia are widely spread obligate intracellular fungal pathogens from vertebrate and invertebrate organisms, mainly transmitted by contaminated food and water. This study aims to detect the presence of major human-pathogenic microsporidia, i.e., Enterocytozoon bieneusi, Encephalitozoon intestinalis, Encephalitozoon hellem, and Encephalitozoon cuniculi, in the gastrointestinal tract of commercially harvested marine fish from Mediterranean coast of the Comunidad Valenciana, Eastern Spain. A total of 251 fish, 138 farmed fish and 113 wild fish from commercial fishing were tested by SYBR Green real-time PCR, enabling the simultaneous detection of the four targeted species. E. intestinalis/hellem was found in 1.45% of farmed fish and 7.96% of wild fish, while Enterocytozoonidae was detected in 2.90% and 18.58% of farmed and wild fish, respectively. E. cuniculi was not detected in any of the analyzed specimens. To the authors' knowledge, this is the first report of E. intestinalis/hellem in fish, particularly in marine fish. Although the role of fish in these species' epidemiology remains unknown, this finding points out a potential public health risk linked to fish consumption. Further studies are necessary to characterize these microsporidia in fish hosts better and to elucidate their epidemiological role.

G lugea sp. infecting Sardinella aurita in Algeria

Parasitological examination of the commercially important pelagic fish Sardinella aurita Valenciennes, 1847 (Clupeidae) from the Eastern coast of Algeria revealed xenomas in the peritoneal cavity, suggesting a microsporidian infection. The prevalence of the disease was approximately 30% on average, higher in smaller individuals and showing significant seasonal variation. The xenomas contained numerous ellipsoidal spores, surrounded by a dense layer of connective tissue. Spore sizes were 6.10 ± 0.38 µm length and 3.54 ± 0.43 µm width. Ultrastructural examination by transmission electron microscopy showed various development stages of the parasite, including meronts, sporonts, sporoblasts and mature spores. The internal organization of the mature spores, with a single nucleus, prominent posterior vacuole, a lamellar polaroplast and an isofilar polar tube arranged in a single row, was typical of the genus Glugea. The DNA sequence of the small subunit ribosomal RNA gene confirmed that this parasite belongs to the genus Glugea. Genetic and morphologic comparison with G. sardinellensis, a species previously described in the same host from Tunisia shows many similarities, although some molecular and morphometric inconsistencies precluded the unambiguous assignment of our samples to G. sardinellensis. At the same time, we do not find sufficient grounds to erect a new taxon for our parasite. We discuss the implications of our findings for the current state of the systematics of Glugea.

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.

Rodlet cells, fish immune cells and a sentinel of parasitic harm in teleost organs

Rodlet cells (RCs) are the enigmatic and distinctive pear-shaped cells had found in many tissues of marine and freshwater teleosts. They have a distinctive fibrous capsule or the cell cortex that envelopes conspicuous inclusions called rodlets, basally situated nucleus, and poorly developed mitochondria. The contraction of the cell cortex results in the expulsion of the cell contents through an apical opening. One hundred and thirty years since rodlet cells were first reported, many questions remain about their origin and a function. This review will present new evidence regarding the relationship between RCs and metazoan parasites, and a protozoan infecting organs of different fish species, and update the state of knowledge about the origin, structure and the function of these intriguing fish cells.

Enterocytozoon schreckii n. sp. Infects the Enterocytes of Adult Chinook Salmon (Oncorhynchus tshawytscha) and May Be a Sentinel of Immunosenescence

A novel Enterocytozoon infection was identified in the intestines of sexually mature Chinook salmon. While microsporidian parasites are common across a diverse range of animal hosts, this novel species is remarkable because it demonstrates biological, pathological, and genetic similarity with Enterocytozoon bieneusi, the most common causative agent of microsporidiosis in AIDS patients. There are similarities in the immune and endocrine processes of sexually mature Pacific salmon and immunocompromised humans, suggesting possible common mechanisms of susceptibility in these two highly divergent host species. The discovery of Enterocytozoon schreckii n. sp. contributes to clarifying the phylogenetic relationships within family Enterocytozoonidae. The phylogenetic and morphological features of this species support the redescription of Enterocytozoon to include Enterospora as a junior synonym. Furthermore, the discovery of this novel parasite may have important implications for conservation, as it could be a sentinel of immune suppression, disease, and prespawning mortality in threatened populations of salmonids.

IMPORTANCE In this work, we describe a new microsporidian species that infects the enterocytes of Chinook salmon. This novel pathogen is closely related to Enterocytozoon bieneusi, an opportunistic pathogen commonly found in AIDS patients and other severely immunocompromised humans. The discovery of this novel pathogen is of interest because it has only been found in sexually mature Chinook salmon, which have compromised immune systems due to the stresses of migration and maturation and which share similar pathological features with immunocompromised and senescent humans. The discovery of this novel pathogen could lead to new insights regarding how microsporidiosis relates to immunosuppression across animal hosts.

Recent Advances with Fish Microsporidia

There have been several significant new findings regarding Microsporidia of fishes over the last decade. Here we provide an update on new taxa, new hosts and new diseases in captive and wild fishes since 2013. The importance of microsporidiosis continues to increase with the rapid growth of finfish aquaculture and the dramatic increase in the use of zebrafish as a model in biomedical research. In addition to reviewing new taxa and microsporidian diseases, we include discussions on advances with diagnostic methods, impacts of microsporidia on fish beyond morbidity and mortality, novel findings with transmission and invertebrate hosts, and a summary of the phylogenetics of fish microsporidia.

Morphological and phylogenetic characterization of a new microsporidium, Triwangia gracilipes n. sp. From the freshwater shrimp Caridina gracilipes (Decapoda: Atyidae) in China

A new microsporidian species was described from the freshwater shrimp Caridina gracilipes collected from Lake Luoma located in Northern Jiangsu province, East China. The infected shrimps appeared generally opaque due to the presence of white cysts located in the connective tissues of the surface of the hepatopancreas. The earliest developmental stages observed were diplokaryotic meronts which were in direct contact with the host cell cytoplasm. Multinucleate sporogonial plasmodia developed into uninucleate sporoblasts which were enclosed in sporophorous vesicles. The parasite developed synchronously within an individual sporophorous vesicle. Mature spores were pyriform and monokaryotic, measuring 5.45 ± 0.18 (5.12-5.82) µm long and 3.57 ± 0.17 (3.18-3.92) µm wide. Anisofilar polar filaments coiled 10-12 turns and arranged in one row. Phylogenetic analysis based on the obtained SSU rDNA sequence indicated that the present species clustered with Triwangia caridina with high support value to form an independent branch which was placed at the basal position of a large clade of containing microsporidia of fishes, crustaceans and amphipods. Based on the morphological characters and ultrastructural features, as well as SSU rDNA-inferred phylogenetic relationships, a new species was erected and named as Triwangia gracilipes n. sp. The taxonomic affiliation of Triwangia was also primarily explored.

Microsporidiosis in Humans

Microsporidia are obligate intracellular pathogens identified ∼150 years ago as the cause of pébrine, an economically important infection in silkworms. There are about 220 genera and 1,700 species of microsporidia, which are classified based on their ultrastructural features, developmental cycle, host-parasite relationship, and molecular analysis. Phylogenetic analysis suggests that microsporidia are related to the fungi, being grouped with the Cryptomycota as a basal branch or sister group to the fungi. Microsporidia can be transmitted by food and water and are likely zoonotic, as they parasitize a wide range of invertebrate and vertebrate hosts. Infection in humans occurs in both immunocompetent and immunodeficient hosts, e.g., in patients with organ transplantation, patients with advanced human immunodeficiency virus (HIV) infection, and patients receiving immune modulatory therapy such as anti-tumor necrosis factor alpha antibody. Clusters of infections due to latent infection in transplanted organs have also been demonstrated. Gastrointestinal infection is the most common manifestation; however, microsporidia can infect virtually any organ system, and infection has resulted in keratitis, myositis, cholecystitis, sinusitis, and encephalitis. Both albendazole and fumagillin have efficacy for the treatment of various species of microsporidia; however, albendazole has limited efficacy for the treatment of Enterocytozoon bieneusi. In addition, immune restoration can lead to resolution of infection. While the prevalence rate of microsporidiosis in patients with AIDS has fallen in the United States, due to the widespread use of combination antiretroviral therapy (cART), infection continues to occur throughout the world and is still seen in the United States in the setting of cART if a low CD4 count persists.

Experimental Horizontal Transmission of Enterospora nucleophila (Microsporea: Enterocytozoonidae) in Gilthead Sea Bream (Sparus aurata)

Enterospora nucleophila is a microsporidian enteroparasite that infects mainly the intestine of gilthead sea bream (Sparus aurata), leading to an emaciative syndrome. Thus far, the only available information about this infection comes from natural outbreaks in farmed fish. The aim of the present study was to determine whether E. nucleophila could be transmitted horizontally using naturally infected fish as donors, and to establish an experimental in vivo procedure to study this host-parasite model without depending on natural infections. Naïve fish were exposed to the infection by cohabitation, effluent, or intubated either orally or anally with intestinal scrapings of donor fish in four different trials. We succeeded in detecting parasite in naïve fish in all the challenges, but the infection level and the disease signs were always milder than in donor fish. The parasite was found in peripheral blood of naïve fish at 4 weeks post-challenge (wpc) in oral and effluent routes, and up to 12 wpc in the anal transmission trial. Molecular diagnosis detected E. nucleophila in other organs besides intestine, such as gills, liver, stomach or heart, although the intensity was not as high as in the target tissue. The infection tended to disappear through time in all the challenge routes assayed, except in the anal infection route.

Enterocytozoon bieneusi of animals-With an 'Australian twist'

Enterocytozoon bieneusi is a microsporidian microorganism that causes intestinal disease in animals including humans. E. bieneusi is an obligate intracellular pathogen, typically causing severe or chronic diarrhoea, malabsorption and/or wasting. Currently, E. bieneusi is recognised as a fungus, although its exact classification remains contentious. The transmission of E. bieneusi can occur from person to person and/or animals to people. Transmission is usually via the faecal-oral route through E. bieneusi spore-contaminated water, environment or food, or direct contact with infected individuals. Enterocytozoon bieneusi genotypes are usually identified and classified by PCR-based sequencing of the internal transcribed spacer region (ITS) of nuclear ribosomal DNA. To date, ~600 distinct genotypes of E. bieneusi have been recorded in ~170 species of animals, including various orders of mammals and reptiles as well as insects in >40 countries. Moreover, E. bieneusi has also been found in recreational water, irrigation water, and treated raw- and waste-waters. Although many studies have been conducted on the epidemiology of E. bieneusi, prevalence surveys of animals and humans are scant in some countries, such as Australia, and transmission routes of individual genotypes and related risk factors are poorly understood. This article/chapter reviews aspects of the taxonomy, biology and epidemiology of E. bieneusi; the diagnosis, treatment and prevention of microsporidiosis; critically appraises the naming system for E. bieneusi genotypes as well as the phylogenetic relationships of these genotypes; provides new insights into the prevalence and genetic composition of E. bieneusi populations in animals in parts of Australia using molecular epidemiological tools; and proposes some areas for future research in the E. bieneusi/microsporidiosis field.

3-Dimensional organization and dynamics of the microsporidian polar tube invasion machinery

Microsporidia, a divergent group of single-celled eukaryotic parasites, harness a specialized harpoon-like invasion apparatus called the polar tube (PT) to gain entry into host cells. The PT is tightly coiled within the transmissible extracellular spore, and is about 20 times the length of the spore. Once triggered, the PT is rapidly ejected and is thought to penetrate the host cell, acting as a conduit for the transfer of infectious cargo into the host. The organization of this specialized infection apparatus in the spore, how it is deployed, and how the nucleus and other large cargo are transported through the narrow PT are not well understood. Here we use serial block-face scanning electron microscopy to reveal the 3-dimensional architecture of the PT and its relative spatial orientation to other organelles within the spore. Using high-speed optical microscopy, we also capture and quantify the entire PT germination process of three human-infecting microsporidian species in vitro: Anncaliia algerae, Encephalitozoon hellem and E. intestinalis. Our results show that the emerging PT experiences very high accelerating forces to reach velocities exceeding 300 μm⋅s-1, and that firing kinetics differ markedly between species. Live-cell imaging reveals that the nucleus, which is at least 7 times larger than the diameter of the PT, undergoes extreme deformation to fit through the narrow tube, and moves at speeds comparable to PT extension. Our study sheds new light on the 3-dimensional organization, dynamics, and mechanism of PT extrusion, and shows how infectious cargo moves through the tube to initiate infection.

Enterospora nucleophila (Microsporidia) in Gilthead Sea Bream (Sparus aurata): Pathological Effects and Cellular Immune Response in Natural Infections

Enterospora nucleophila is a microsporidian responsible for an emaciative disease in gilthead sea bream (Sparus aurata). Its intranuclear development and the lack of in vitro and in vivo models hinder its research. This study investigated the associated lesions, its detection by quantitative polymerase chain reaction, and the cellular immune response of naturally infected fish. The intensity of infection in the intestine was correlated with stunted growth and reduced body condition. At the beginning of the outbreaks, infection prevalence was highest in intestine and stomach, and in subsequent months, the prevalence decreased in the intestine and increased in hematopoietic organs and stomach. In heavy infections, the intestine had histologic lesions of enterocyte hypercellularity and proliferation of rodlet cells. Infected enterocytes had E. nucleophila spores in the cytoplasm, and a pyknotic nucleus, karyorhexis or karyolysis. Lymphocytes were present at the base of the mucosa, and eosinophilic granule cells were located between the enterocytes. In intestinal submucosa, macrophage aggregates containing spores were surrounded by lymphocytes and granulocytes, with submucosal infiltration of granulocytes. Macrophage aggregates appeared to develop into granulomata with necrotic areas containing parasite remnants. Immunohistochemistry revealed mast cells as the main type of granulocyte involved. Abundant IgM⁺ and IgT⁺ cells were identified by in situ hybridization in the submucosa when intracytoplasmic stages were present. This study describes the lesions of E. nucleophila in gilthead sea bream, an important aquaculture species.

Challenge for macrophages and mast cells of Chelon ramada to counter an intestinal microparasite, Myxobolus mugchelo (Myxozoa)

Thinlip mullet Chelon ramada is the most abundant mullet species found in the Comacchio lagoons (northern Adriatic Sea, Italy). Histological and ultrastructural sections of the intestine of C. ramada showed that over 83% of 48 mullets were infected with the intestinal parasite Myxobolus mugchelo (Myxozoa). In histological sections, plasmodia of M. mugchelo containing mature spores were situated closer to mucosal folds and were surrounded by numerous mast cells (MCs). Mature spores, generally oval in shape, were observed in the paracellular space among the enterocytes or within them. Near the infected epithelial cells, several MCs, rodlet cells and few neutrophils occurred. In intestinal epithelium, large cells resembling macrophages, some with spores of M. mugchelo inside, were observed. These macrophage-like cells were foamy and possessed elongate striated granules. The number of MCs and macrophages in the intestinal epithelium was significantly higher in parasitized fish. In some parasitized intestines, portions of epithelium were displaced by spores, or the spores were observed inside the damaged enterocytes. Immunohistochemical analysis of C. ramada infected or uninfected intestinal tissue revealed the presence of histamine, serotonin (5-HT), leu-enkephalin and inducible-nitric oxide synthase in epithelial macrophages. Several epithelial cells positive to proliferating cell-nuclear antigen were also observed in the proximity of the macrophages. The current study is the first to record the occurrence of intraepithelial macrophages which engulf myxozoan spores. A hypothesis on migration of spores from pancreas via intestinal wall to gut lumen is presented.

Evaluation and Microanalysis of Parasitic and Bacterial Agents of Egyptian Fresh Sushi, Salmo salar

The present study aimed to evaluate the quality of fresh sushi in Egypt. Fifty samples of sushi (Salmo salar) were collected from restaurants in Alexandria, Egypt. Paraffin, semi-thin and ultra-thin sections were used for parasitological analysis by light and transmission electron microscopy. Bacteria were isolated by the dilution plate and direct plate methods and identified by a Vitek system. Twenty (40%) of the total examined samples showed microsporidia and helminth metacercariae infections. Histochemical stains showed distinct pinkish-red pyriform microspores embedded in muscular tissue stained with Gram, periodic acid-Schiff (PAS), and Ziehl-Neelsen (ZN) stains. Semi-thin sections showed double membrane xenoma-inducing granulomas containing spores at different developmental stages. Empty sporophorous vesicles and free spores were observed in the electron microscopic images. A bacteriological assay showed forty samples (80%) contaminated with human pathogenic bacteria with the average total bacterial counts ranging from 32 to 526 CFU/g. Four species of human pathogenic bacteria were identified in the examined samples, namely Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus, and Serratia plymuthica in 40, 38, 11, and 6 samples, respectively. These constitute the first record of fresh sushi product in Egypt and indicate the potential pathogenicity associated with raw seafood products.

Detection of the intranuclear microsporidian Enterospora nucleophila in gilthead sea bream by in situ hybridization

Enterospora nucleophila is an intranuclear microsporidian responsible for emaciative microsporidiosis of gilthead sea bream (GSB). Its minute size and cryptic nature make it easily misdiagnosed. An in situ hybridization (ISH) technique based on antisense oligonucleotide probes specific for the parasite was developed and used in clinically infected GSB in combination with calcofluor white stain (CW) and other histopathological techniques. The ISH method was found to label very conspicuously the cells containing parasite stages, with the signal concentrating in merogonial and sporogonial plasmodia within the infected cell nuclei. Comparison with CW demonstrated limited ISH signal in cells containing mature spores, which was attributed mostly to the scarcity of probe targets present in these stages. Although spores were detected in other organs of the digestive system as well as in the peripheral blood, proliferative stages or parasite reservoirs were not found in this work outside the intestines. The study demonstrated a frequent disassociation between the presence of abundant spores and the intensity of the infections as determined by the parasite activity. The ISH allows confirmatory diagnosis of GSB microsporidiosis and estimation of infection intensity and will be a valuable tool for a more precise determination of parasite dissemination pathways and pathogeny mechanisms.

Histopathological and ultrastructural assessment of two mugilid species infected with myxozoans and helminths

The histopathology and ultrastructure of the intestine of mullets, Liza ramada and Liza saliens, from Comacchio lagoons (northern Italy) naturally infected with myxozoans and helminths were investigated and described. Sixty-two (80.5%) of 77 mullets harboured one or more of the following parasites species: Myxobolus mugchelo (Myxozoa), Neoechinorhynchus agilis (Acanthocephala), Haplosplanchnus pachysomus and Dicrogaster contractus (Digenea). Co-occurrence of helminths with myxozoans was common. The main damage caused by digeneans was destruction of the mucosal epithelium of the villi, necrosis and degeneration of intestinal epithelial cells. More severe intestinal damage was caused by acanthocephalans which reach the submucosa layer with their proboscis. At the site of helminths infection, several mast cells (MCs), rodlet cells (RCs), mucous cells and few neutrophils and macrophages were observed in the epithelium. RCs and mucous cells exhibited discharge activity in close vicinity to the worm's tegument. M. mugchelo conspicuous plasmodia were encysted mainly in muscle and submucosa layers of the intestine. Indeed, spores of M. mugchelo were documented within the epithelial cells of host intestine and in proximity to MCs. Degranulation of the MCs near the myxozoans was very frequent.

A case study of Desmozoon lepeophtherii infection in farmed Atlantic salmon associated with gill disease, peritonitis, intestinal infection, stunted growth, and increased mortality

Background

In September 2008, a disease outbreak characterized by acute, severe gill pathology and peritonitis, involving the gastrointestinal tract, was observed in an Atlantic salmon (Salmo salar L.) farm in north-western Norway. During subsequent sampling in November 2008 and January 2009, chronic proliferative gill inflammation and peritonitis was observed. Cumulative mortalities of 5.6–12.8% and severe growth retardation were observed. Routine diagnostic analysis revealed no diseases known to salmon at the time, but microsporidian infection of tissues was observed.

Methods

To characterize the disease outbreak, a combination of histopathology, in situ hybridization (ISH), chitin, calcofluor-white (CFW) staining, and real-time PCR were used to describe the disease progression with visualization of the D. lepeophtherii stages in situ.

Results

The presence of the microsporidian Desmozoon lepeophtherii was confirmed with real-time PCR, DNA sequencing and ISH, and the parasite was detected in association with acute lesions in the gills and peritoneum. ISH using a probe specific to small subunit 16S rRNA gene provided an effective tool for demonstrating the distribution of D. lepeophtherii in the tissue. Infection in the peritoneum seemed localized in and around pre-existing vaccine granulomas, and in the gastrointestinal walls. In the heart, kidney and spleen, the infection was most often associated with mononuclear leucocytes and macrophages, including melanomacrophages. Desmozoon lepeophtherii exospores were found in the nuclei of the gastrointestinal epithelium for the first time, suggesting a role of the gastrointestinal tract in the spread of spores to the environment.

Conclusions

This study describes the progression of D. lepeophtherii disease outbreak in an Atlantic salmon farm without any other known diseases present. Using different methods to examine the disease outbreak, new insight into the pathology of D. lepeophtherii was obtained. The parasite was localized in situ in association with severe tissue damage and inflammation in the gills, peritoneal cavity and in the gastrointestinal (GI) tract that links the parasite directly to the observed pathology.

Outbreak of enteric microsporidiosis of hatchery-bred juvenile groupers, Epinephelus spp., associated with a new intranuclear microporidian in China

A new enteric microsporidian was found to be associated with the mass mortality of hatchery-bred juvenile groupers, Epinephelus spp., in China. The outbreak usually occurred during the rainy season between May and November when water temperature ranged from 26 to 30 °C and salinity from 28 to 34 ppt, although this microsporidian can be detected year round. External clinical signs included severe emaciation, white faeces syndrome, anorexia, sinking to the bottom of culture ponds and mass mortality (up to 90%). Upon necropsy, severe intestinal oedema and thin and transparent intestinal wall could be observed. The mature spores are tiny, measuring 1.3-1.5 (1.35 ± 0.13) × 1.6-2.4 (2.16 ± 0.31) μm and can be found in the cytoplasm and the nucleoplasm of most enteric epithelial cells of host. Epidemiological investigation showed that this species was distributed throughout most of the culture area of grouper fingerlings in Fujian, Guangdong, Hainan and Guangxi provinces in China, with maximum prevalence of 95%. Molecular analysis based on the partial small subunit rRNA sequence (1045 bp) placed this species within the Enterocytozoonidae, but sequence identities to other species were below 90%. The exact taxonomic position warrants study of the ultrastructural characteristics of the developmental stages.

A Nested PCR Assay to Avoid False Positive Detection of the Microsporidian Enterocytozoon hepatopenaei (EHP) in Environmental Samples in Shrimp Farms

Hepatopancreatic microsporidiosis (HPM) caused by Enterocytozoon hepatopenaei (EHP) is an important disease of cultivated shrimp. Heavy infections may lead to retarded growth and unprofitable harvests. Existing PCR detection methods target the EHP small subunit ribosomal RNA (SSU rRNA) gene (SSU-PCR). However, we discovered that they can give false positive test results due to cross reactivity of the SSU-PCR primers with DNA from closely related microsporidia that infect other aquatic organisms. This is problematic for investigating and monitoring EHP infection pathways. To overcome this problem, a sensitive and specific nested PCR method was developed for detection of the spore wall protein (SWP) gene of EHP (SWP-PCR). The new SWP-PCR method did not produce false positive results from closely related microsporidia. The first PCR step of the SWP-PCR method was 100 times (104 plasmid copies per reaction vial) more sensitive than that of the existing SSU-PCR method (106 copies) but sensitivity was equal for both in the nested step (10 copies). Since the hepatopancreas of cultivated shrimp is not currently known to be infected with microsporidia other than EHP, the SSU-PCR methods are still valid for analyzing hepatopancreatic samples despite the lower sensitivity than the SWP-PCR method. However, due to its greater specificity and sensitivity, we recommend that the SWP-PCR method be used to screen for EHP in feces, feed and environmental samples for potential EHP carriers.

Immunity to gastrointestinal microparasites of fish

Fish intestinal parasites cause direct mortalities and also morbidity, poor growth, higher susceptibility to opportunistic pathogens and lower resistance to stress. This review is focused on microscopic parasites (Protozoa and Metazoa) that invade the gastrointestinal tract of fish. Intracellular parasites (mainly Microsporidia and Apicomplexa) evoke almost no host immune reaction while they are concealed in the cytoplasmic and nuclear compartments, and can even use fish cells (macrophages) as Trojan horses to spread in the host. Inflammatory reaction only appears when the parasite bursts infected cells. Immunity against extracellular parasites is depicted for the myxozoans Ceratonova shasta and Enteromyxum spp. The cellular and humoral innate responses and the production of antibodies are crucial for resolving some of these myxozoonoses, but an excessive inflammatory reaction (concerted by cytokines) can become a fatal pathophysiological consequence. The local immune response plays a key role, with numerous genes more strongly regulated in the intestine than at lymphohaematopoietic organs.

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.

Occurrence of immune cells in the intestinal wall of Squalius cephalus infected with Pomphorhynchus laevis

A sub-population of 34 specimens of chub, Squalius cephalus, was sampled from the River Brenta (Northern Italy) and examined for ecto- and endo-parasites. Pomphorhynchus laevis (Acanthocephala) was the only enteric helminth encountered. Immunofluorescence and ultrastructural studies were conducted on the intestines of chub. Near the site of parasite's attachment, mucous cells, mast cells (MCs), neutrophils and rodlet cells (RCs) were found to co-occur within the intestinal epithelium. The numbers of mucous cells, MCs and neutrophils were significantly higher in infected fish (Mann-Whitney U test, p < 0.05). Dual immunofluorescence staining with the lectin Dolichos Biflorus Agglutinin (DBA) and the macrophage-specific MAC387 monoclonal antibody, with parallel transmission electron microscopy, revealed that epithelial MCs often made intimate contact with the mucous cells. Degranulation of a large number of MCs around the site of the acanthocephalan's attachment and in proximity to mucous cells was also documented. MCs and neutrophils were abundant in the submucosa. Immune cells of the intestinal epithelium have been described at the ultrastructural level and their possible functions and interactions are discussed.

Rediscovery of Nucleophaga amoebae, a novel member of the Rozellomycota

Recent studies showed that the huge diversity branching at or near the phylogenetic root of the fungal kingdom, mostly constituted by uncultured environmental clones, is actually characterized by intracellular predators/parasites of various eukaryotes. These form three related lineages: the Aphelidea, endoparasites of algae; the Rozellomycota, with Rozella species mainly endoparasites of water moulds, and Paramicrosporidium species endonuclear parasites of amoebae; and the Microsporidia, mainly endoparasites of animals. Increasing evidence suggests the emergence of Microsporidia from within Rozellomycota; however, their fungal or protistan nature is still unclear. Here, we report the molecular phylogeny based on the small subunit ribosomal RNA (SSU rDNA) gene, of an additional endoparasite of amoebae, corresponding to the old enigmatic chytrid Nucleophaga amoebae described in the nineteenth century. Our results show that Nucleophaga, possessing a morphotype intermediate between Rozella and Paramicrosporidium, emerges as a unique lineage within the Rozellomycota. The recovery and characterization of new members of Rozellomycota are of high value for the understanding of the early evolutionary history of the Fungi and related lineages.