Khoo, L.; Rommel, F.; Smith, S.; Griffin, M.; Pote, L.
2010
Myxobolus neurophilus: morphologic, histopathologic and molecular characterization
Diseases of Aquatic Organisms
89: 51-61
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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 for the presence of Myxobolus
neurophilus. Archived tissues were sectioned and stained with hematoxylin and eosin or with
Giemsa, revealing myxozoan spores consistent with M. neurophilus. The myxospores 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 fresh submissions of all 5 fish species revealed similar myxozoan
spores only in the brains of yellow perch. These were Giemsa-positive, with no iodinophilous
vacuoles evident. Portions of the affected brains were fixed in neutral buffered 10% formalin and
sectioned for histology. Pseudocysts containing myxospores were only evident in sections of the
brains and spinal cords of yellow perch. Mild mononuclear meningoencephalitis was present when
myxospores appeared outside of the pseudocysts. Brains fixed in 5% gluteraldehyde for scanning
electron microscopic examination revealed pyriform myxospores with a smooth capsular surface.
Sequencing and phylogenetic analysis of the 18S small subunit ribosomal DNA gene placed the
organism within the family Myxobolidae, with no direct matches to sequences available via
GenBank. Aquatic annelids from sediment obtained from the affected pond were negative for
actinospores.