Heterosporis anguillarum infections in farm cultured eels (Anguilla japonica) in Korea

Tetra disseminated microsporidiosis: a novel disease in ornamental fish caused by Fusasporis stethaprioni n. gen. n. sp

A novel microsporidial disease was documented in two ornamental fish species, black tetra Gymnocorymbus ternetzi Boulenger 1895 and cardinal tetra Paracheirodon axelrodi Schultz 1956. The non-xenoma-forming microsporidium occurred diffusely in most internal organs and the gill, thus referring to the condition as tetra disseminated microsporidiosis (TDM). The occurrence of TDM in black tetra was associated with chronic mortality in a domestic farmed population, while the case in cardinal tetra occurred in moribund fish while in quarantine at a public aquarium. Histology showed that coelomic visceral organs were frequently necrotic and severely disrupted by extensive infiltrates of macrophages. Infected macrophages were presumed responsible for the dissemination of spores throughout the body. Ultrastructural characteristics of the parasite developmental cycle included uninucleate meronts directly in the host cell cytoplasm. Sporonts were bi-nucleated as a result of karyokinesis and a parasite-produced sporophorous vesicle (SPV) became apparent at this stage. Cytokinesis resulted in two spores forming within each SPV. Spores were uniform in size, measuring about 3.9 ± 0.33 long by 2.0 ± 0.2 μm wide. Ultrastructure demonstrated two spore types, one with 9-12 polar filament coils and a double-layered exospore and a second type with 4-7 polar filament coils and a homogenously electron-dense exospore, with differences perhaps related to parasite transmission mechanisms. The 16S rDNA sequences showed closest identity to the genus Glugea (≈ 92%), though the developmental cycle, specifically being a non-xenoma-forming species and having two spores forming within a SPV, did not fit within the genus. Based on combined phylogenetic and ultrastructural characteristics, a new genus (Fusasporis) is proposed, with F. stethaprioni n. gen. n. sp. as the type species.

Ultrastructural and Molecular Characterisation of an Heterosporis-Like Microsporidian in Australian Sea Snakes (Hydrophiinae)

Four sea snakes (two Hydrophis major, one Hydrophis platurus, one Hydrophis elegans) were found washed ashore on different beaches in the Sunshine Coast region and Fraser Island in Queensland, Australia between 2007–2013. Each snake had multiple granulomas and locally extensive regions of pallor evident in the hypaxial and intercostal musculature along the body. Lesions in two individuals were also associated with vertebral and rib fractures. Histological examination revealed granulomas scattered throughout skeletal muscle, subcutaneous adipose tissue and fractured bone. These were composed of dense aggregates of microsporidian spores surrounded by a mantle of macrophages. Sequences (ssrRNA) were obtained from lesions in three sea snakes and all revealed 99% similarity with Heterosporis anguillarum from the Japanese eel (Anguillarum japonica). However, ultrastructural characteristics of the organism were not consistent with those of previous descriptions. Electron microscopic examination of skeletal muscle revealed large cysts (not xenomas) bound by walls of fibrillar material (Heterosporis-like sporophorocyst walls were not detected). The cysts contained numerous mature microsporidian spores arranged in small clusters, sometimes apparently within sporophorous vesicles. The microspores were monomorphic, oval and measured 2.5–3.0 μm by 1.6–1.8 μm. They contained isofilar polar filaments with 11 (infrequently 9–12) coils arranged in two ranks. This is the first published report of a microsporidian infection in hydrophiid sea snakes. This discovery shows microsporidia with molecular affinities to Heterosporis anguillarum but ultrastructural characters most consistent with the genus Pleistophora (but no hitherto described species). Further studies are required to determine whether the microsporidian presented here belongs to the genus Heterosporis, or to a polymorphic species group as suggested by the recognition of a robust Pleistophora/Heterosporis clade by molecular studies. The gross and histological pathology associated with these infections are described.

Description of the Microsporidian Parasite, Heterosporis sutherlandae n. sp., Infecting Fish in the Great Lakes Region, USA

Heterosporosis is an increasingly important microsporidian disease worldwide, impacting wild and farmed raised fishes in both marine and freshwater environments. A previously undescribed species (Heterosporis sp.), with widespread distribution in the Great Lakes region, was the subject of this study. Three angler-caught fish were submitted to the Minnesota Veterinary Diagnostic Laboratory from 2009–2010 with lesions caused by intracellular proliferation of parasitic spores, resulting in destruction and eventual widespread necrosis of the host skeletal muscles. Mature ovoid (5.8 x 3.5μm) spores of a microsporidian parasite, consistent with the genus Heterosporis, were observed by light and electron microscopy. Molecular identification was performed using primer walking to obtain a near-complete rRNA gene sequence (~3,600 bp). A unique species of Heterosporis was identified, demonstrating less than 96% sequence identity to other published Heterosporis sp. on the basis of partial rRNA gene sequence analysis. Heterosporis sutherlandae n. sp. (formerly Heterosporis sp.) was identified in yellow perch (Perca flavescens), northern pike (Esox lucius) and walleye (Sander vitreus) from inland lakes in Minnesota and Wisconsin. Previous research suggests this species may be even more widespread in the Great Lakes region and should be reexamined using molecular techniques to better understand the distribution of this novel species.

Morphological and molecular biological characterization of Pleistophora aegyptiaca sp. nov. infecting the Red Sea fish Saurida tumbil

One hundred three out of 225 (45.8%) of the Red Sea fish Saurida tumbil were infected with microsporidian parasites. The infection was recorded as tumor-like masses (whitish macroscopic cysts) or xenomas often up to 2 cm in diameter and embedded in the peritoneal cavity. Generally, the infection was increased during winter 63.8% (86 out of 135) and fall to 18.9% (17 out of 90) in summer. Light microscopic study revealed that xenomas were encapsulated by a fibrous layer encircling numerous sporophorous vesicles filled with mature spores measuring 1.7 ± 0.6 (1.5-2.7 μm) × 1.5 ± 0.3 μm (1.2-1.8 μm) in size. Ultrastructural microscopic study showed the presence of smooth membranes of the sarcoplasmic reticulum forming a thick, amorphous coat surrounding various developmental stages of the parasite. The various recognizable stages of the parasite were uninuclear, binucleated, and multinucleated meronts followed by detachment of the plasmalemma of the sporont from the sporophorous vesicle producing sporoblasts. Mature spores consist of a spore coat and spore contents. The spore contents consist of the uninucleated sporoplasm and a posterior vacuole located at the posterior end. The polar tube consists of a straight shaft and a coiled region (26-32 coils) arranged in many rows along the inside periphery of the spore. The polaroplast consisted of an anterior region of closely and loosely packed membranes. Molecular analysis based on the small subunit rDNA gene was performed to determine the phylogenetic position of the present species. The percentage identity between this species and a range of other microsporidia predominantly from aquatic hosts demonstrated a high degree of similarity (>92%) with eight Pleistophora species. Comparison of the nucleotide sequences and divergence showed that the sequence of the present microsporidium was most similar to that of Pleistophora anguillarum (99.8% identity) differing in 13 nucleotide positions. So, the present species was recorded and phylogenetically positioned as a new species of Pleistophora.