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Diseases of Aquatic Organisms

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DAO 60:105-108 (2004)  -  doi:10.3354/dao060105

Myxobolus cerebralis internal transcribed spacer 1 (ITS-1) sequences support recent spread of the parasite to North America and within Europe

Christopher M. Whipps1,*, Mansour El-Matbouli2, Ronald P. Hedrick3, Vicki Blazer4,Michael L. Kent1

1Department of Microbiology, Center for Fish Disease Research, 220 Nash Hall, Oregon State University, Corvallis, Oregon 97331-3404, USA
2Institut für Zoologie, Fischerei-Biologie und Fischkrankheiten der Universität München, Kaulbachstr. 37, 80539 München, Germany
3Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California 95616, USA
4US Geological Survey, National Fish Health Research Laboratory, Leetown Science Center, 11700 Leetown Road, Kearneysville, West Virginia 25430, USA

ABSTRACT: Molecular approaches for resolving relationships among the Myxozoa have relied mainly on small subunit (SSU) ribosomal DNA (rDNA) sequence analysis. This region of the gene is generally used for higher phylogenetic studies, and the conservative nature of this gene may make it inadequate for intraspecific comparisons. Previous intraspecific studies of Myxobolus cerebralis based on molecular analyses reported that the sequence of SSU rDNA and the internal transcribed spacer (ITS) were highly conserved in representatives of the parasite from North America and Europe. Considering that the ITS is usually a more variable region than the SSU, we reanalyzed available sequences on GenBank and obtained sequences from other M. cerebralis representatives from the states of California and West Virginia in the USA and from Germany and Russia. With the exception of 7 base pairs, most of the sequence designated as ITS-1 in GenBank was a highly conserved portion of the rDNA near the 3-prime end of the SSU region. Nonetheless, the additional ITS-1 sequences obtained from the available geographic representatives were well conserved. It is unlikely that we would have observed virtually identical ITS-1 sequences between European and American M. cerebralis samples had it spread naturally over time, particularly when compared to the variation seen between isolates of another myxozoan (Kudoa thyrsites) that has most likely spread naturally. These data further support the hypothesis that the current distribution of M. cerebralis in North America is a result of recent introductions followed by dispersal via anthropogenic means, largely through the stocking of infected trout for sport fishing.

KEY WORDS: Myxozoa · Ribosomal DNA · Myxobolus cerebralis · Whirling disease · Internal transcribed spacer

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