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

Characterizing Two New Henneguya Species in the Respiratory Organs of African Sharptooth Catfish

Henneguya species are myxozoans, a suborder of Cnidaria, which can affect the gills and extrarespiratory organs of the African sharptooth catfish, Clarias gariepinus. This research describes natural infection-induced histological alterations caused by the Henneguya species present. The Henneguya species were also identified molecularly using DNA sequenced from infected tissue cysts, and phylogenetically analyzed. Clinical investigations revealed cyst-like nodules on the fish gill filaments and extrarespiratory organs. Within a milky fluid inside the cysts were several Henneguya-like spores. Henneguya sp. infested 27.5% of the fish, with the highest prevalence in the gills compared to the extrarespiratory organs. The Henneguya species parasitized the gill and the dendritic tissues, resulting in histopathological characteristics. The plasmodia's developmental stages resulted in destructive damage which manifested as marked necrosis, which was replaced by a focal aggregation of inflammatory cells. Amplification of the 18S ribosomal DNA from the fish parasites was followed by sequencing, which confirmed their identities as new species Henneguya qenabranchiae n. sp. and Henneguya qenasuprabranchiae n. sp. with 99.53 and 99.64% identities, respectively, to Henneguya sp. 1 HS-2015. The two C. gariepinus myxozoans shared some characteristics based on morphologic and phylogenetic analysis as previously published, where it was proposed that they were a sister lineage to Henneguya species in Egypt, and it is now proposed that they are new species.

Plasmodium structure of Intoshia linei (Orthonectida)

Orthonectids are enigmatic parasitic bilaterians whose exact position on the phylogenetic tree is still uncertain. Despite ongoing debate about their phylogenetic position, the parasitic stage of orthonectids known as "plasmodium" remains underexplored. There is still no consensus on the origin of the plasmodium: whether it is an altered host cell or a parasitic organism that develops in the host extracellular environment. To determine the origin of the orthonectid parasitic stage, we studied in detail the fine structure of the Intoshia linei orthonectid plasmodium using a variety of morphological methods. The orthonectid plasmodium is a shapeless multinucleated organism separated from host tissues by a double membrane envelope. Besides numerous nuclei, its cytoplasm contains organelles typical for other bilaterians, reproductive cells, and maturing sexual specimens. Reproductive cells, as well as developing orthonectid males and females, are covered by an additional membrane. The plasmodium forms protrusions directed to the surface of the host body and used by mature individuals for egress from the host. The obtained results indicate that the orthonectid plasmodium is an extracellular parasite. A possible mechanism for its formation might involve spreading parasitic larva cells across the host tissues with subsequent generation of a cell-within-cell complex. The cytoplasm of the plasmodium originates from the outer cell, which undergoes multiple nuclear divisions without cytokinesis, while the inner cell divides, giving rise to reproductive cells and embryos. The term "plasmodium" should be avoided and the term "orthonectid plasmodium" could be temporarily used instead.

Increasing the known biodiversity of cnidarian parasites of bryconid fishes from South America: two novel Myxobolus species with ultrastructure and ssrDNA-based phylogeny

This study increases the known biodiversity of cnidarian parasites in neotropical bryconid fishes. Two novel Myxobolus species are described based on morphology, ultrastructure and small subunit ribosomal DNA (ssrDNA) sequencing: Myxobolus vetuschicanus n. sp. infecting fins of Salminus franciscanus and Myxobolus mineirus n. sp. infecting the mesentery of Brycon orthotaenia from the São Francisco River basin, Minas Gerais State, Brazil. Ultrastructural analysis of the two species revealed an asynchronous sporogenesis process, with germinative cells and young developmental stages of myxospores in the periphery of the plasmodia. In M. vetuschicanus n. sp., the plasmodia were surrounded by a layer of fibroblasts and in M. mineirus n. sp., the plasmodial membrane had direct contact with the host tissue. The phylogenetic analysis based on the ssrDNA of Henneguya/Myxobolus species showed that the two novel Myxobolus species grouped in subclades together with other parasite species of bryconid fishes.

Morphological, ultrastructural, and phylogenetic analysis of two novel Myxobolus species (Cnidaria: Myxosporea) parasitizing bryconid fish from São Francisco River, Brazil

Twelve Myxobolus species have been previously described to parasitize Bryconidae fish in South America. Here, we describe two novel myxosporean species that parasitize economically important Bryconidae from the São Francisco River basin in Brazil. Myxospores morphometry, morphology, small-subunit ribosomal DNA - ssrDNA sequences, and other biological traits were used in the taxonomic analysis. Phylogenetic analysis was performed to assess the position of the new Myxobolus species among the closest Myxobolus/Henneguya. Myxobolus iecoris n. sp. was found infecting the liver of Salminus franciscanus (dourado). Myxospores were oval with the anterior region aculiform in frontal view and biconvex in lateral view and measured 11.4-14.2 (12.8 ± 0.8) μm long, 7.7-9.9 (8.7 ± 0.6) μm wide, 6.5-7.5 (6.9 ± 0.4) μm thick. Two pyriform and equal-sized polar capsules measuring 4.9-7.4 (5.9 ± 0.5) μm long and 2.3-3.5 (3.0 ± 0.2) μm wide contained polar tubules with 8-9 turns. Myxobolus lienis n. sp. was found infecting the spleen of Brycon orthotaenia (matrinxã). Myxospores were round to oval in frontal view and biconvex in lateral view and measured 10.3-13.8 (12 ± 0.6) μm long, 6.8-9.3 (8.3 ± 0.5) μm wide, and 6.9-7.0 (7.0 ± 0.6) μm thick. Two oval and equal-sized polar capsules measured 3.9-5.8 (4.6 ± 0.5) μm long and 2.0-3.5 (2.8 ± 0.3) μm wide contained polar tubules with 5-6 turns. Ultrastructural analysis revealed asynchronous sporogenesis with germinative cells and young sporogonic stages in the periphery of the plasmodia. A connective tissue capsule was observed surrounding Myxobolus lienis n. sp., but it was absent for Myxobolus iecoris n. sp. Maximum likelihood and Bayesian inferences showed the two novel species clustering in a well-supported subclade composed by Myxobolus spp. of bryconids. Myxobolus iecoris n. sp. appeared as a sister species of M. aureus and Myxobolus lienis n. sp. as sister to M. umidus.

Histopathological and ultrastructural studies of Myxobolus turpisrotundus from allogynogenetic gibel carp Carassius auratus gibelio in China

During an ongoing systematic survey on species diversity of myxozoans parasitising allogynogenetic gibel carp Carassius auratus gibelio (Bloch) in China, plasmodia were detected in the fins, lip, jaw, gill chamber, gill arches, operculum and oral cavity of infected fish. Combining the morphological and molecular data, the present species was identified as Myxobolus turpisrotundus Zhang, Wang, Li et Gong, 2010. Histopathological examination revealed that despite infecting different organs, M. turpisrotundus always occurred in dermis, demonstrating its affinity to this tissue. Histopathological effect of M. turpisrotundus on the host is relatively mild except parasites in the gill arches producing compression of the adipose tissue and heavy adductor muscles deformation with lymphohistiocytic infiltrates. In addition, the plasmodia in different sites were with the same complex structure arrangement: cup-like cells with unknown derivation, a thin collagenous fibril layer, areolar connective tissue, basement membrane and host epithelial cell. Ultrastructural analysis showed that the parasite has monosporic pansporoblast and sporogenesis followed the usual pattern of most of the myxosporeans.

Histological location of myxosporean plasmodia in fish tissue with Luna's method

In the present study, a staining technique, Luna's method, has been used for detection and tissue location of myxosporean spores/plasmodia in histological sections of gills and liver. The Luna's staining was performed on the sections of the tissue fixed in Bouin's, embedded in paraffin wax. The mature plasmodia were stained in bright red color and pansporoblasts and gill tissue stained in blue. This staining helped to detect and locate even a single myxospore of less than 15 μm in size located within the tissues of the host.

Histopathological and ultrastructural studies of a Henneguya species (Myxozoa: Myxosporea) infesting the intestine of Clarias gariepinus from Benin (West Africa)

Fish culture is the best alternative to fill the gap between natural fish catches and estimated needs of populations in animal protein consumption. In West Africa, this goal required to have suitable fishes for aquaculture which are Clariidae and Tilapia. Clarias gariepinus (Clariidae) fetches a higher price than tilapias as it can be sold alive at the market but a high infestation by Henneguya leads to decrease this commercial value. Those reasons lead us to perform studies on seasonal variations, histopathological aspects and life cycle of Henneguya sp. infecting the intestine of C. gariepinus using light and electron microscope. From November 2011 to December 2012, 339 specimens were collected from Ouémé River (Benin) and examined. An overall prevalence of 7.37 % was recorded for plasmodia of Henneguya sp. Parasite occurrence did not vary significantly between seasons (χ(2) = 12.235; df = 3; p > 0.05), nor sexes (χ(2) = 2.992; df = 7; p > 0.05) while differences were significant between classes of weight (χ(2) = 39.929; df = 5; p < 0.05). The highest prevalence was recorded in host ranging from 300 to 374 g. Histopathological analysis showed that the mass continuous development of the plasmodium produced thickening of the intestine wall and compressed neighboring tissues and destroyed villi and smooth muscle layers. The stages of the parasite development including sporogenesis, capsulogenesis, and valvogenesis were asynchronous. Investigations are still running by molecular approaches in order to identify accurately this species.

18S rRNA gene sequencing identifies a novel species of Henneguya parasitizing the gills of the channel catfish (Ictaluridae)

In the southeastern USA, the channel catfish Ictalurus punctatus is a host to at least eight different species of myxozoan parasites belonging to the genus Henneguya, four of which have been characterized molecularly using sequencing of the small subunit ribosomal RNA (SSU rRNA) gene. However, only two of these have confirmed life cycles that involve the oligochaete Dero digitata as the definitive host. During a health screening of farm-raised channel catfish, several fish presented with deformed primary lamellae. Lamellae harbored large, nodular, white pseudocysts 1.25 mm in diameter, and upon rupturing, these pseudocysts released Henneguya myxospores, with a typical lanceolate-shaped spore body, measuring 17.1 ± 1.0 μm (mean ± SD; range = 15.0-19.3 μm) in length and 4.8 ± 0.4 μm (3.7-5.6 μm) in width. Pyriform-shaped polar capsules were 5.8 ± 0.3 μm in length (5.1-6.4 μm) and 1.7 ± 0.1 μm (1.4-1.9 μm) in width. The two caudal processes were 40.0 ± 5.1 μm in length (29.5-50.0 μm) with a spore length of 57.2 ± 4.7 (46.8-66.8 μm). The contiguous SSU rRNA gene sequence obtained from myxospores of five excised cysts did not match any Henneguya sp. in GenBank. The greatest sequence homology (91% over 1,900 bp) was with Henneguya pellis, associated with blister-like lesions on the skin of blue catfish Ictalurus furcatus. Based on the unique combination of pseudocyst and myxospore morphology, tissue location, host, and SSU rRNA gene sequence data, we report this isolate to be a previously unreported species, Henneguya bulbosus sp. nov.

Henneguya cuniculator sp. nov., a parasite of spotted sorubim Pseudoplatystoma corruscans in the São Francisco Basin, Brazil

Henneguya cuniculator sp. nov. was found infecting spotted sorubim catfish Pseudoplatystoma corruscans from the São Francisco River, Minas Gerais, Brazil. The parasites form elongated plasmodia of up to 1 cm in length in the gill filaments. Mature spores were ellipsoidal from the frontal view, with total length of 29.4 ± 2.4 (mean ± SD, range 23.3-32.4) µm, body length of 12.1 ± 1.0 (10.0-14.7) µm, width of 4.8 ± 0.4 (4.0-5.9) µm, and tail length of 16.7 ± 2.0 (12.3-19.4) µm. From the lateral view, spores were biconvex, with thickness of 4.2 ± 0.7 (3.9-4.9) µm. The polar capsules were elongated and equal in size, 6.2 ± 0.3 (5.2-6.2) µm in length, and 1.8 ± 0.1 (1.4-1.9) µm in width. Ultrastructural analysis showed that the plasmodial wall had delicate projections towards the host tissue and a thin layer that prevented contact between the host cells and the parasite. In the ectoplasm, few mitochondria were observed, while generative cells, early stages of sporogenesis, and advanced spore development occurred in the plasmodial periphery, and more mature spores in internal regions. Histopathological analysis showed that plasmodia developed in the sub-epithelial connective tissue of gill filaments, causing compression of the adjacent tissues, deformation of gill filaments, and lamellar fusion. Phylogenetic analysis, based on 18S rDNA genes and using only Henneguya/Myxobolus species parasites of siluriform fish, showed grouping according to the fish family.

First report of Kudoa species (Myxozoa: Kudoidae) infecting the spotted coral grouper Plectropomus maculates from the Red Sea. A light and ultrastructural study

In the present study, out of 200, 120 (60%) Plectropomus maculates fish were found to be naturally infected with Kudoa sp. The infection was intensive and appeared as clusters of ovoid to ellipsoidal plasmodia being restricted to the cardiac muscles. More than 100 plasmodia were counted per infected heart and measured 1.53 ± 0.2 (1.2-2.5) × 0.65 ± 0.2 (0.63-0.80) mm. On the basis of spore morphology, the parasite was identified as Kudoa sp. The spore measures 4.8 ± 0.3 (4.7-6.8) × .0 ± 0.3 (4.6-6.5) μm. The four polar capsules were pyrifom in shape measuring 1.4 ± 0.2 (1.3-3.5) × 1.2 ± 0.2 (1.1-2.2) μm. Transmission electron microscopy showed that the plasmodia were bordered by a single membrane which invaginates into pinocytotic canals. Adjacent to the plasmodial wall, the generative cells and the early pansporoblasts were located peripherally. The developmental stages characterizing sporogenesis, capsulogenisis, and valvogenesis of the present parasites were ultrastructurally studied.

Morphology and small subunit ribosomal DNA sequence of Henneguya suprabranchiae (Myxozoa), a parasite of the catfish Clarias gariepinus (Clariidae) from the River Nile, Egypt

Forty-three out of 120 (35.8%) Clarias garipenus fish were found to be naturally infected with Henneguya suprabanchiae. The infection appeared as clusters of ovoid to ellipsoidal plasmodia being embedded within the hyaline cartilage of the suprabranchial organ of the fish. Histological studies indicate tissue distortion at the sites of infection. The continuous growth of the plasmodium led to deformation of the filament structure as well as disorganization and displacement of the gill lamellae. Also, a severe atrophy occurred in the hyaline cartilage of the gills and also in the gill lamellae. Based on the structure and measurements of fresh spores by light microscopy, this parasite was identified as H. suprabranchiae. Spores are oval in shape, and they measure 13 (11-14) × 3 (2-5) μm length by width. It has two polar capsules inside, each measures 3 (2.5-5) × 1 (1.5-4) μm length by width. Each polar capsule has a spirally coiled (7-9 turns) polar filament. The ultrastructural analysis showed that the plasmodia were surrounded by single-unit membrane. The generative cells and the early developmental stages were arranged at the periphery of the plasmodia, while immature and mature spores were centrally arranged. The developmental stages characterizing sporogenesis, capsulogenisis, and valvogenesis of the present parasite were ultrastructurally studied. The small subunit 18 S rDNA (SSU rDNA) gene sequences from different isolates was sequenced and compared with the sequence of the same gene from the Henneguya sp. isolated from GenBank. The phylogenetic position of the present Henneguya sp. within the genus was determined using sequence analysis of all related taxa available in GenBank, and the phylogenetic tree derived from this study is elucidated and compared with the current taxonomy of the available myxosporeans. Comparison of the nucleotide sequences and divergence showed that the SSU rDNA gene of this Henneguya species revealed 92.2% sequence identity with Henneguya exilis (acc. no. AF021881) differing in 30 nucleotides with lower divergence value.

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.