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

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Abstract

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.

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Data availability

Histology slides were submitted to the National Parasite Collection housed at the Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology, under catalog numbers USNM1638543–USNM1638546. Genetic sequence of the small subunit rDNA was deposited to GenBank under accession number MW077214. Original histology blocks and resin-embedded blocks are maintained at the Tropical Aquaculture Laboratory, University of Florida and the Office of Fish and Wildlife Health and Forensics Laboratory, NJ Division of Fish and Wildlife, respectively.

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Acknowledgments

The authors thank John Leary and Dr. Lowia Al-Hussinee for assistance with processing samples for molecular analyses.

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This study was funded by combined internal funds from the authors’ host laboratories.

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Correspondence to J. Lovy.

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Section Editor: Shokoofeh Shamsi

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Lovy, J., Yanong, R.P.E., Stilwell, J.M. et al. Tetra disseminated microsporidiosis: a novel disease in ornamental fish caused by Fusasporis stethaprioni n. gen. n. sp.. Parasitol Res 120, 497–514 (2021). https://doi.org/10.1007/s00436-020-06988-7

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  • DOI: https://doi.org/10.1007/s00436-020-06988-7

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