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

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 Resale or republication not permitted without written consent of the publisherDis Aquat Org 51: [113][114][115][116][117][118][119][120][121] 2002 clines among wild rainbow trout populations in the states of Idaho, Montana, Colorado and Utah, USA (Nehring & Walker 1996, Vincent 1996, Hedrick et al. 1998. M. cerebralis is the best known of 1300 parasites grouped in the phylum Myxozoa and the first shown to possess a 2 host life cycle including salmonid fish and an aquatic oligochaete, Tubifex tubifex (Markiw & Wolf 1983, Wolf & Markiw 1984, Wolf et al. 1986). The parasite has been observed among wild fish in 23 states in the USA, but without the same disastrous effects observed in the intermountain west (Nickum 1999). The differences in the impacts on wild fish between geographic region...

Identification of a serine protease gene expressed by Myxobolus cerebralis during development in rainbow trout Oncorhynchus mykiss

“…Eliminating parasite infestations from fishrearing facilities has focused on disrupting the life cycle of the parasite by chemically disinfecting ponds and raceways and using water sources free of fishes or oligochaetes. Managing whirling disease among wild salmonid populations has been more difficult, with major efforts focused on prohibiting stocking with infected farm-reared fishes and reducing conditions that contribute to habitats that may increase the populations of susceptible oligochaetes (Beauchamp et al 2002, Wagner 2002. Detecting M. cerebralis among populations of captive or wild fish stocks is a key step in controlling the spread of whirling disease.…”

Accelerated deactivation of Myxobolus cerebralis myxospores by susceptible and non-susceptible Tubifex tubifex

“…Lineage I worms from the Gallatin River in Montana, did produce a few TAMs when the dosage was 1000 myxospores worm −1 (Kerans et al 2004). Likewise, 77% of Lineage I oligochaetes from Windy Gap Reservoir, Colorado, that were exposed to 6000 myxospores worm −1 did release some TAMs (Beauchamp et al 2002).…”

“…Deactivation of myxospores in the natural environment by these tubificids could reduce or eliminate M. cerebralis infections where they were the dominant oligochaete (Beauchamp et al 2002, 2006, Kerans et al 2004, Nehring et al 2013. The objective of our study was to answer that question.…”

“…These research efforts were focused on both aspects of the parasite life cycle. Application of polymerase chain reaction (PCR) technology (Andree et al 1998, Baldwin & Myklebust 2002, Cavender et al 2004) molecular biology (Sturmbauer et al 1999, Beauchamp et al 2001) and other state-of-the-art analytical techniques led to rapid advances and a deeper understanding of the etiology of M. cerebralis in the aquatic oligochaete host T. tubifex (Gilbert & Granath 2001, Beauchamp et al 2002, 2006, Nehring et al 2013. Beauchamp et al (2001) developed mitochondrial 16S ribosomal DNA markers to parse the T. tubifex species-complex into 6 distinct lineages.…”

Effect of cadmium on the susceptibility of Tubifex tubifex to Myxobolus cerebralis (Myxozoa), the causative agent of whirling disease

“…However, T. tubifex is highly polymorphic and its susceptibility to pollutants and the parasite is highly variable. To date, 6 mitochondrial lineages (I to VI) of T. tubifex have been distinguished (Beauchamp et al 2001, Sturmbauer et al 1999, and only lineages I (in some cases) and III are susceptible to M. cerebralis (Beauchamp et al 2002, DuBey et al 2005. Moreover, tolerance against pollutants differs between the lineages (Sturmbauer et al 1999).…”