Paradoxium irvingi n.gen. n.sp. (Microsporidia) infecting the musculature of European pink shrimp Pandalus montagui

Paospora carinifang n. gen., n. sp. (Microsporidia: Spragueidae), a parasite of the ridgetail white prawn, Palaemon carinicauda

A new microsporidian disease of the pond-reared ridgetail white prawn, Palaemon carinicauda, was found in China. Light microscopy, pathology, and scanning electron microscopy showed that the parasite infected the host's skeletal muscle tissue and formed spherical sporophorous vesicles (SPOVs). Electron microscopy revealed that its merogonic life stages developed in direct contact with the host cytoplasm. The sporogonic life stages underwent octosporoblastic sporogony with the formation of eight uninucleate spores in each SPOV. Fresh SPOVs were 5.4 ± 0.55 µm in diameter. The octospores were oval and measured 2.3 × 1.5 μm (fresh) and 1.96 × 1.17 μm (fixed). The isofilar polar filament was coiled with 9-10 turns and arranged in two rows. Phylogenetic analysis based on the SSU rRNA gene suggests that this microsporidium has close affinities with members of the genera Potaspora and Apotaspora, but represents an independent generic taxon. We therefore propose the establishment of a new genus and species (Paospora carinifang n. gen., n. sp.) within the family Spragueidae. We also propose a taxonomic revision to transfer Potaspora macrobrachium to this new genus and reclassify it as Paospora macrobrachium comb. nov.

Revising the Freshwater Thelohania to Astathelohania gen. et comb. nov., and Description of Two New Species

Crayfish are common hosts of microsporidian parasites, prominently from the genus Thelohania. Thelohania is a polyphyletic genus, with multiple genetically distinct lineages found from freshwater and marine environments. Researchers have been calling for a revision of this group for over a decade. We provide evidence that crayfish-infecting freshwater Thelohania are genetically and phylogenetically distinct from the marine Thelohania (Clade V/Glugeida), whilst also describing two new species that give further support to the taxonomic revision. We propose that the freshwater Thelohania should be transferred to their own genus, Astathelohania gen. et comb. nov., in a new family (Astathelohaniidae n. fam.). This results in the revision of Thelohania contejeani (Astathelohania contejeani), Thelohania montirivulorum (Astathelohania montirivulorum), and Thelohania parastaci (Astathelohania parastaci). We also describe two novel muscle-infecting Astathelohania species, A. virili n. sp. and A. rusti n. sp., from North American crayfishes (Faxonius sp.). We used histological, molecular, and ultrastructural data to formally describe the novel isolates. Our data suggest that the Astathelohania are genetically distinct from other known microsporidian genera, outside any described family, and that their SSU rRNA gene sequence diversity follows their host species and native geographic location. The range of this genus currently includes North America, Europe, and Australia.

Ultrastructural and molecular study of the microsporidian Toguebayea baccigeri n. gen., n. sp., a hyperparasite of the digenean trematode Bacciger israelensis (Faustulidae), a parasite of Boops boops (Teleostei, Sparidae)

A new microsporidian Toguebayea baccigeri n. gen., n. sp., hyperparasite of Bacciger israelensis (Digenea, Faustulidae), parasite of Boops boops (Teleostei, Sparidae) is described by means of transmission electron microscopy. The phylogenetic analysis, based on the SSU rDNA gene, places the new species in the clade containing mainly crustacean-infecting microsporidia of the genus Cucumispora, within superclade V (Marinosporidia) sensu Vossbrinck et al., 2014. Mature spores of T. baccigeri are ovoid, uninucleated and measure 2.5 × 1.4 μm. The number of coils of the polar tube is 8–10. The polaroplast is composed of an external lamellar part and an internal vesicular or granular part. The main differences that distinguish the new genus and new species from the closely related microsporidia include hyperparasitism in a digenean host infecting a marine fish, the geographic distribution (coast of Tunisia), presence of one nucleus at all developmental stages, disporoblastic sporogony, and the absence of sporophorous vacuoles.

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.

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.

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.

A novel dimorphic microsporidian Ameson iseebi sp. nov. infecting muscle of the Japanese spiny lobster, Panulirus japonicus, in western Japan

Japanese spiny lobsters (Panulirus japonicus) exhibiting white opaque abdominal muscle were found in Mie and Wakayama prefectures, in mid-Western Japan. Microscopically, two types of microsporidian spores, ovoid and rod-shaped, were observed infecting the muscle. Histologically, both types of spore were detected inside myofibers of the abdomen, appendages, and cardiac muscles and were often both observed in a single myofiber simultaneously. Transmission electron microscopy revealed that ovoid spores have villous projections on the surface, and that ovoid and rod-shaped spores have a polar filament with 12 coils and 6 to 8 coils respectively. Merogonic and sporogonic stages were observed around ovoid spores, but rarely around rod-shaped spores. The small subunit ribosomal DNA sequences obtained from both spore types were identical to each other, indicating that this microsporidian exhibits a clear spore dimorphism. Phylogenetic analysis based on the rDNA sequences indicates that this microsporidian is part of a clade consisting of the genera Ameson and Nadelspora, with the most closely related species being A. herrnkindi found in the Caribbean spiny lobster P. argus. Based on ultrastructural features, molecular phylogenetic data, host type and geographical differences among known species in these genera, the species found in whitened abdominal muscles of the Japanese spiny lobster is described as Ameson iseebi sp. nov.

Invertebrate host responses to microsporidia infections

Microsporidia are a group of fungi-like intracellular and unicellular parasites, which infect nearly all animals. As "master parasites", over 1400 microsporidian species have been described to date. Microsporidia infections in economical invertebrates (e.g., silkworm, shrimp) cause huge financial losses, while other microsporidia infections in daphnia, nematode, locust, honeybee and mosquito play important roles in the regulation of their population size. Research investigating invertebrate host responses following microsporidia infections has yielded numerous interesting results, especially pertaining to the innate immune response to these pathogens. In this review, we comparatively summarize the invertebrate host responses to various microsporidia infections. We discuss numerous critical events in host responses including ubiquitin-mediated resistance, production of reactive oxygen species, melanization and innate immune pathways, and the increased basic metabolism and the accumulation of juvenile hormone in infected hosts. Recent studies progressing our understanding of microsporidia infection are also highlighted. Collectively, these advances shed more light on general rules of invertebrate host immune responses and pathogenesis mechanisms of microsporidia, and concurrently offer valuable clues for further research on the crosstalk between hosts and intracellular pathogens.

Evidence for trophic transfer ofInodosporus octosporaandOvipleistophora arlon. sp. (Microsporidia) between crustacean and fish hosts

Within aquatic habitats, the hyper-abundant Order Crustacea appear to be the predominant host group for members of the Phylum Microsporidia. The musculature, a common site of infection, provides access to biochemical (carbohydrate-rich) and physiological (mitochondria-rich) conditions conducive to prolific parasite replication and maturation. The significant proportion of body plan devoted to skeletal musculature in Crustacea provides the location for a highly efficient intracellular parasite factory. In this study, we utilize histological, ultrastructural and phylogenetic evidence to describe a previously known (Inodosporus octospora) and novel (Ovipleistophora arlon. sp.) microsporidian parasites infecting the musculature of the common prawn (Palaemon serratus) from the same site, at the same time of year. Despite similar clinical signs of infection, both parasites are otherwise distinct in terms of pathogenesis, morphology and phylogeny. Based upon partial subunit ribosomal RNA (SSU rDNA) sequence, we show that thatI. octosporamay be identical to aKabatanasp. previously described infecting two-spot goby (Gobiusculus flavescens) in Europe, or at least thatInodosporusandKabatanagenera are synonyms. In addition, SSU rDNA sequence forO. arloplaces it within a distinct clade containingOvipleistophora mirandellaeandOvipleistophora ovariae, both infecting the oocytes of freshwater fish in Europe. Taken together, our data provide strong evidence for trophic-transfer between crustacean and fish hosts for two different microsporidians within clade 5 of the phylum. Furthermore, it demonstrates that morphologically and phylogenetically distinct microsporidians can infect the same tissues of the same host species to impart clinical signs which mimic infection with the other.

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.