Oligochaete Populations in Transylvania County Trout Streams: A Risk Assessment of Susceptibility to the Whirling Disease Parasite, Myxobolus Cerebralis

Overview

Myxobolus cerebralis is a myxosporean parasite diminishing healthy salmonid populations throughout the United States via an infection known as “whirling disease”. Currently there is no treatment for whirling disease─consequently rendering commercial and wild salmonid populations vulnerable to widespread infection. M. cerebralis myxospores maintain a two-staged life cycle, first asexually maturing within the intestine of the Tubifex tubifex oligochaeta. There are currently six known genetic variants (I-VI) of T. tubifex; variant (III) being most susceptible to M. cerebralis myxospores, while variant (VI) is most resistant to the myxospores. This study is the first reported to identify oligochaete compositions within major freshwater ecosystems in Transylvania County. Initial research determined that oligochaetes can be found in environments that contain large amounts of biological oxygen demanding agents, soft nutrient-rich substrate, and little to no current flow. Research was completed based on the hypothesis that T. tubifex oligochaetes would not represent a substantial presence in Transylvania County, due to the lack of an accommodating habitat. Substrate samples were collected from the Davidson and French Broad Rivers using a small shovel device that allowed for consistent, approximate substrate densities. Samples were stored in a freezer at -20℃. DNA extractions were completed, followed by PCR and gel electrophoresis using three primer varieties: TUB16, 16S and ITS1A/Tt1r. Results from seven gels showed that─from the samples collected─the majority were L. hoffmeisteri, a species of oligochaete not susceptible to M. cerebralis. These data support the statement that Transylvania County is not at significant risk for whirling disease outbreak.