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Diseases of Aquatic Organisms

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DAO 51:113-121 (2002)  -  doi:10.3354/dao051113

Prevalence and susceptibility of infection to Myxobolus cerebralis, and genetic differences among populations of Tubifex tubifex

Katherine A. Beauchamp1,*, Melanie Gay1, Garry O. Kelley1, Mansour El-Matbouli2, R. Deedee Kathman3, R. Barry Nehring4, Ronald P. Hedrick1

1Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California 95616, USA
2Institute of Zoology, Fish Biology and Fish Diseases, Faculty of Veterinary Medicine, University of Munich, Kaulbachstr. 37, 80539 Munich, Germany
3Aquatic Resources Center, College Grove, Tennessee 37046, USA
4Colorado Division of Wildlife, 2300 Townsend Avenue, Montrose, Colorado 81401, USA

ABSTRACT: The prevalence of infection and susceptibility of the aquatic oligochaete Tubifex tubifex to Myxobolus cerebralis, was examined in 2 studies on the upper Colorado River, Colorado, USA, where whirling disease occurs in wild trout populations. In the first study, the prevalence of infection ranged from 0.4 to 1.5%, as determined by counting the number of T. tubifex releasing triactinomyxons of M. cerebralis directly following their collection from the field. The susceptibility of those T. tubifex not releasing triactinomyxons was assessed by the number of these oligochaetes releasing triactinomyxons 3 mo following experimental exposures to spores of M. cerebralis. The prevalence of infection following experimental exposures of these T. tubifex ranged from 4.2 to 14.1%. In a second study, all T. tubifex collected at 2 different times directly from the 2 field sites in Colorado were exposed to spores of M. cerebralis. Individual oligochaetes representing those groups of T. tubifex releasing and those groups not releasing triactinomyxons at 3 mo were screened with molecular genetic markers. T. tubifex populations found at the 2 study sites consisted of 4 genetically distinct lineages that varied with respect to their susceptibility to experimental exposure to M. cerebralis. Lineages I and III contained the most oligochaetes susceptible to M. cerebralis and were the most prominent lineages at Windy Gap Reservoir, a site of high infectivity for wild rainbow trout on the upper Colorado River. In contrast, at the Breeze Bridge site which is below Windy Gap Reservoir and where M. cerebralis infections are less severe in wild trout, oligochaetes in lineages V and VI that are resistant to M. cerebralis were more prominent. These results suggest that certain habitats, such as Windy Gap Reservoir, are conducive to large and more homogenous populations of susceptible T. tubifex lineages that may serve as point sources of infection for M. cerebralis. Although not a direct objective of this study, there was no evidence of M. cerebralis infections among any oligochaetes other than those that would be classified as T. tubifex by standard morphological characteristics.

KEY WORDS: Whirling disease · Myxobolus cerebralis · Tubifex tubifex

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