Molecular characterization of the myxosporean associated with parasitic encephalitis of farmed Atlantic salmon Salmo salar in Ireland

S. Frasca, D. R. Linfert, G. J. Tsongalis, T. S. Gorton, A. E. Garmendia, Ronald Hedrick, A. B. West, H. J. Van Kruiningen

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

During seasonal epizootics of neurologic disease and mass mortality in the summers of 1992, 1993 and 1994 on a sea-farm in Ireland, Atlantic salmon Salmo salar smolts suffered from encephalitis associated with infection by a neurotropic parasite. Based on ultrastructural studies, this neurotropic parasite was identified as an intercellular presporogonic multicellular developmental stage of a histozoic myxosporean, possibly a Myxobolus species. In order to generate sequence data for phylogenetic comparisons to substantiate the present morphological identification of this myxosporean in the absence of detectable sporogony, polymerase chain reaction (PCR), Southern blot hybridization, dideoxynucleotide chain-termination DNA sequencing, and in situ hybridization (ISH) were used in concert to characterize segments of the small subunit ribosomal RNA (SSU rRNA) gene. Oligonucleotide primers were created from sequences of the SSU rRNA gene of M. cerebralis and were employed in PCR experiments using DNA extracted from formalin-fixed paraffin-embedded tissue sections of brains from Atlantic salmon smolts in which the myxosporean had been detected by light microscopy. Five segments of the SSU rRNA gene of the myxosporean, ranging in length from 187 to 287 base pairs, were amplified, detected by hybridization with sequence-specific probes, and sequenced. Consensus sequences from these segments were aligned to create a partial sequence of the SSU rRNA gene of the myxosporean. Assessments of sequence identity were made between this partial sequence and sequences of SSU rRNA genes from 7 myxosporeans, including Ceratomyxa shasta, Henneguya doori, M. arcticus, M. cerebralis, M. insidiosus, M. neurobius, and M. squamalis. The partial SSU rRNA gene sequence from the myxosporean had more sequence identity with SSU rRNA gene sequences from neurotropic and myotropic species of Myxobolus than to those from epitheliotropic species of Myxobolus or Henneguya, or the enterotropic species of Ceratomyxa, and was identical to regions of the SSU rRNA gene of M. cerebralis. Digoxigenin-labeled oligonucleotide DNA probes complementary to multiple segments of the SSU rRNA gene of M. cerebralis hybridized with DNA of the parasite in histologic sections of brain in ISH experiments demonstrating definitively that the segments of genome amplified were from the organisms identified by histology and ultrastructural analysis. Based on sequence data derived entirely from genetic material of extrasporogonic stages, the SSU rDNA sequence identity discovered in this study supports the hypothesis that the myxosporean associated with encephalitis of farmed Atlantic salmon smolts is a neurotropic species of the genus Myxobolus, with sequences identical to those of M. cerebralis.

Original languageEnglish (US)
Pages (from-to)221-233
Number of pages13
JournalDiseases of Aquatic Organisms
Volume35
Issue number3
StatePublished - Feb 26 1999

Fingerprint

encephalitis
Ireland
Salmo salar
RNA
ribosomal RNA
Myxobolus
gene
smolts
Ceratomyxa
smolt
Henneguya
Myxobolus cerebralis
genes
DNA
parasite
parasites
in situ hybridization
polymerase chain reaction
hybridization
brain

Keywords

  • Atlantic salmon
  • In situ hybridization
  • Myxobolus cerebralis
  • Myxosporean
  • PCR
  • Small subunit ribosomal DNA

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science

Cite this

Frasca, S., Linfert, D. R., Tsongalis, G. J., Gorton, T. S., Garmendia, A. E., Hedrick, R., ... Van Kruiningen, H. J. (1999). Molecular characterization of the myxosporean associated with parasitic encephalitis of farmed Atlantic salmon Salmo salar in Ireland. Diseases of Aquatic Organisms, 35(3), 221-233.

Molecular characterization of the myxosporean associated with parasitic encephalitis of farmed Atlantic salmon Salmo salar in Ireland. / Frasca, S.; Linfert, D. R.; Tsongalis, G. J.; Gorton, T. S.; Garmendia, A. E.; Hedrick, Ronald; West, A. B.; Van Kruiningen, H. J.

In: Diseases of Aquatic Organisms, Vol. 35, No. 3, 26.02.1999, p. 221-233.

Research output: Contribution to journalArticle

Frasca, S, Linfert, DR, Tsongalis, GJ, Gorton, TS, Garmendia, AE, Hedrick, R, West, AB & Van Kruiningen, HJ 1999, 'Molecular characterization of the myxosporean associated with parasitic encephalitis of farmed Atlantic salmon Salmo salar in Ireland', Diseases of Aquatic Organisms, vol. 35, no. 3, pp. 221-233.
Frasca, S. ; Linfert, D. R. ; Tsongalis, G. J. ; Gorton, T. S. ; Garmendia, A. E. ; Hedrick, Ronald ; West, A. B. ; Van Kruiningen, H. J. / Molecular characterization of the myxosporean associated with parasitic encephalitis of farmed Atlantic salmon Salmo salar in Ireland. In: Diseases of Aquatic Organisms. 1999 ; Vol. 35, No. 3. pp. 221-233.
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AU - Frasca, S.

AU - Linfert, D. R.

AU - Tsongalis, G. J.

AU - Gorton, T. S.

AU - Garmendia, A. E.

AU - Hedrick, Ronald

AU - West, A. B.

AU - Van Kruiningen, H. J.

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KW - Myxosporean

KW - PCR

KW - Small subunit ribosomal DNA

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