An unidentified epi-epithelial myxosporean in the intestine of gilthead sea bream Sparus aurata L

Digestive and immune functions in the intestine of wild Ballan wrasse (Labrus bergylta)

This study was carried out to profile key characteristics of intestinal functions and health in wild-caught Ballan wrasse. To describe functional variation along the intestine, samples were collected from four intestinal segments, named from the proximal to the distal segment: IN1, IN2, IN3 and IN4. The sections showed quite similar structure, i.e. regarding mucosal fold height and branching, lamina propria and submucosal width and cellular composition and thickness of the muscle layers. Leucine aminopeptidase and maltase capacity decreased from IN1 to IN4, suggesting a predominant role of IN1 in digestion. Gene expression levels of vitamin C transporter (slc23a1) and fatty acid transporters (cd36 and fabp2) were higher in IN1 than in IN4, indicating a more important role of the proximal intestine regarding transport of vitamins and fatty acids. Higher expression of the gene coding for IgM heavy chain constant region (ighm) was found in IN4 than in IN1, suggesting an important immune function of the distal intestine. Other immune related genes il1b, il6, cd40, showed similar expression in the proximal and the distal part of the intestine. Parasite infection, especially the myxozoan parasite Enteromyxum leei, coincided with infiltration of lymphocytic and eosinophilic granular cells in the submucosa and lamina propria. The present study established reference information necessary for interpretation of results of studies of intestinal functions and health in cultured Ballan wrasse.

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

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

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.

Immunohistochemical characterization of polyclonal antibodies against Enteromyxum leei and Enteromyxum scophthalmi (Myxozoa: Myxosporea), intestinal parasites of fish

The enteric myxozoan parasites Enteromyxum leei (Diamant, Lom et Dyková) and Enteromyxum scophthalmi Palenzuela, Redondo et Álvarez-Pellitero are responsible for high weight loss in infected fish, which leads to subchronic disease and low mortality rates in gilthead sea bream (GSB), Sparus aurata L., and to high mortality rates in turbot, Psetta maxima (L.). The detection of initial parasite stages in histological sections is particularly difficult, but can be simplified by means of specific antibodies. Rabbit polyclonal antibodies (pAbs) were raised against E. scophthalmi and E. leei, and direct enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry were used to characterize their sensitivity and specificity. Both pAbs were adsorbed (apAb) with non-infected intestines to avoid non-specific labelling of fish tissues and to improve their specificity. The highest titre obtained in ELISA was 1: 32 000 for apAb-Eleei and 1:16 000 for apAb-Escoph. Working dilutions in immunohistochemistry were 1:1000 for apAb-Eleei and 1:8000 for apAb-Escoph. Both apAbs labelled proliferative and sporogonic stages with high specificity. apAb-Escoph was very specific, whereas apAb-Eleei cross-reacted with Sphaerospora dicentrarchi Sitjà-Bobadilla et Álvarez-Pellitero and Sphaerospora testicularis Sitjà-Bobadilla et Álvarez-Pellitero, suggesting the presence of shared antigens. These pAbs stand as new tools for antigenic characterization and the diagnosis of both Enteromyxum species.

3D Morphology, ultrastructure and development of Ceratomyxa puntazzi stages: first insights into the mechanisms of motility and budding in the Myxozoa

Free, amoeboid movement of organisms within media as well as substrate-dependent cellular crawling processes of cells and organisms require an actin cytoskeleton. This system is also involved in the cytokinetic processes of all eukaryotic cells. Myxozoan parasites are known for the disease they cause in economical important fishes. Usually, their pathology is related to rapid proliferation in the host. However, the sequences of their development are still poorly understood, especially with regard to pre-sporogonic proliferation mechanisms. The present work employs light microscopy (LM), electron microscopy (SEM, TEM) and confocal laser scanning microscopy (CLSM) in combination with specific stains (Nile Red, DAPI, Phalloidin), to study the three-dimensional morphology, motility, ultrastructure and cellular composition of Ceratomyxa puntazzi, a myxozoan inhabiting the bile of the sharpsnout seabream.

Our results demonstrate the occurrence of two C. puntazzi developmental cycles in the bile, i.e. pre-sporogonic proliferation including frequent budding as well as sporogony, resulting in the formation of durable spore stages and we provide unique details on the ultrastructure and the developmental sequence of bile inhabiting myxozoans. The present study describes, for the first time, the cellular components and mechanisms involved in the motility of myxozoan proliferative stages, and reveals how the same elements are implicated in the processes of budding and cytokinesis in the Myxozoa. We demonstrate that F-actin rich cytoskeletal elements polarize at one end of the parasites and in the filopodia which are rapidly de novo created and re-absorbed, thus facilitating unidirectional parasite motility in the bile. We furthermore discover the myxozoan mechanism of budding as an active, polarization process of cytokinesis, which is independent from a contractile ring and thus differs from the mechanism, generally observed in eurkaryotic cells. We hereby demonstrate that CLSM is a powerful tool for myxozoan research with a great potential for exploitation, and we strongly recommend its future use in combination with in vivo stains.

Some additional data to the occurrence, morphology and validity of Myxobolus turpisrotundus Zhang, 2009 (Myxozoa: Myxosporea)

Myxobolus turpisrotundus Zhang, 2009, infects allogynogenetic gibel carp Carassius auratus gibelio (Bloch) and is always regarded as synonymous with Myxobolus rotundus Nemeczek, 1911, since its first report in goldfish Carassius auratus auratus (L.) in China in 1955. In this study, it was comprehensively examined by morphological and molecular biological methods. The round spores of M. turpisrotundus are similar to those of M. rotundus from common bream Abramis brama (L.) in morphology; however, we detected slight differences in morphometry. The ratios of the length and width of the spore to the length and width of the polar capsule of M. turpisrotundus are usually below 2.0 and 1.9, respectively, however these ratios are always above 2.0 and 1.9 in M. rotundus. The plasmodium size of M. turpisrotundus is 600-6,200 microm in diameter and that of M. rotundus is 60-180 microm in diameter. Scanning observation showed the spore surface of M. turpisrotundus was generally pitted. Yet the surface of M. rotundus is smooth. Sequence comparison revealed the small subunit ribosomal RNA gene sequence of M. turpisrotundus did not match any published sequences of M. rotundus (EU710583, 85% over 742 bp; FJ851447, 85% over 742 bp, FJ851448, 85% over 742 bp; FJ851449, 85% over 742 bp). Moreover, phylogenetic analysis showed M. turpisrotundus clustered with the species from allogynogenetic gibel carp with high bootstrap values (100% neighbor-joining, NJ; 100% maximum parsimony, MP) and M. rotundus from common bream composed a new cluster with high bootstrap values (100% NJ, 100% MP). From the morphological and molecular biological data, we gain enough evidences to support the validity of M. turpisrotundus.

Ultrastructure and host parasite relationships of Kudoa pagrusi (Myxozoa) infecting the heart muscles of sea bream Pagrus pagrus (L.) from the Red Sea

The present study is a part of a continuous investigation of myxosporean parasites-infecting fish of the Red Sea using light and electron microscopy. Out of 120, 80 (67%) Pagrus pagrus fish were found to be naturally infected with Kudoa pagrusi. The infection was intensive and appeared as clusters of ovoid to ellipsoidal plasmodia being restricted to the cardiac muscles. Histological studies elaborated tissue distortion at the sites of infection and the adjacent layers. The development of the plasmodia reduced the functional area of the heart muscle. Ultrastructural analysis showed that the plasmodia were surrounded by single-unit membrane with numerous projections and pinocytotic channels extended toward the host cell. The generative cells and the different developmental stages were arranged at the periphery of the plasmodia while immature and mature spores were centrally arranged. The present study showed the main criteria of this genus: the spores possess four polar capsules with four shell valves.

Light and electron microscopic study on Henneguya suprabranchiae Landsberg, 1987 (Myxozoa: Myxosporea) infecting Oreochromis niloticus, a new host record

Out of 58 live tilapia fish, five Oreochromis niloticus were found to be naturally infected with Henneguya suprabranchiae (8.62%). Such infection was recorded only during winter season from Bahr Shebin, a tributary of the River Nile at Menoufia Governorate, Nile Delta, Egypt. Based on the structure and measurements of fresh spores, this parasite was identified as H. suprabranchiae. Spores are oval in shape and they measure 15 (13-16) x 5 (4-6) microm length by width. It has two polar capsules inside and they measure 4 (5-7) x 1 (2-3) microm length by width. Each polar capsule has spirally coiled (7-9 turns) polar filament. The plasmodia as well as all other parasitic stages were described using light and transmission electron microscopy and discussed regarding to those of other fish hosts especially those of Africa.