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Myxobolus neurophilus: morphologic, histopathologic and molecular characterization

Khoo, Lester, Rommel, Frederick A., Smith, Stephen A., Griffin, Matt J., Pote, Linda M.
Diseases of Aquatic Organisms 2010 v.89 no.1 pp. 51
Annelida, Micropterus dolomieu, Myxobolus, Notemigonus crysoleucas, Perca flavescens, Pimephales promelas, brain, fish diseases, histopathology, inflammation, meningoencephalitis, phylogeny, pond culture, ponds, protozoal infections, ribosomal DNA, sediments, spinal cord, spores, vacuoles
Archived tissues from affected yellow perch (Perca flavescens) as well as fresh submissions of juvenile yellow perch, walleye, fathead minnows, golden shiners and smallmouth bass cultured in the same pond or from a shared water source were examined. Archived tissues were sectioned and stained with hematoxylin and eosin or with Giemsa revealing myxospozoan spores consistent with Myxobolus neurophilus. These were found beneath the ependymal lining of the central canal of the brain or free within the stratum periventriculare with minimal or no inflammation. Unstained and stained (Wright Giemsa or Lugol’s iodine) touch impressions of the brains from all 5 species were prepared, examined microscopically. Only yellow perch were affected by similar myxozoan spores which were Giemsa positive with no iodinophilius vacuoles evident. Portions of the affected brains were fixed in 10% neutral buffered formalin. Pseudocysts containing spores were evident only in the brains and spinal cords of yellow perch in the histological sections. Mild mononuclear meningoencephalitis was present when the spores appeared outside of the pseudocysts. Brains fixed in 5% gluteraldehyde for scanning electron microscopic examination revealed spores with a smooth capsular surface. Phylogenetic analysis of 18S SSU rDNA of the spores revealed no direct matches to sequences available via Genbank and placed the organism within the family Myxobolidae. Aquatic annelids from sediment obtained from the affected pond were negative for actinospores.