Pseudoloma neurophilia n. g., n. sp., a new microsporidium from the central nervous system of the zebrafish (Danio rerio)

An unusual xenoma-forming microsporidium was discovered in the central nerv ous system of moribund zebrafish from a laboratory colony in Eugene, Oregon . Infected fish were often emaciated and lethargic, and histological examin ation commonly revealed severe myelitis and myositis associated with the in fection. Based on its structure, development, and small subunit ribosomal D NA sequence it is unique among fish microsporidia. Spores are uninucleate, ovoid to pyriform, with a prominent posterior vacuole. Spores average 5.4 x 2,7 mum with 13-16 coils of the polar filament. The microsporidium produce s xenomas within the spinal cord and hindbrain of fish, and xenomas contain ed sporophorous vesicles with up to 16 spores. Sporoblasts and presporoblas t stages (probably sporonts) are found occasionally in small aggregates dis persed randomly throughout xenomas. It clustered in the "Ichthyosporidium g roup" along with other fish microsporidian genera based on rDNA sequence an alysis. The rDNA sequence of the zebrafish microsporidium was most similar to that of Ichthyosporidium, but showed only 12.1% similarity and therefore this microsporidium can be considered a distinct genus and species, which we have named Pseudoloma neurophilia n. g.. n. sp.