Ceratonova (formerly Ceratomyxa) shasta, a myxozoan parasite, is the causative agent of the serious intestinal disease ceratomyxosis in salmonids. The parasite lifecycle requires both a salmonid host and an intermediate host, the benthic freshwater polychaete Manayunkia speciosa.1 Traditionally, C. shasta detection methods have included sentinel fish exposures and subsequent histological examination or PCR, parasite spore detection in environmental water samples via filtration and PCR, and intermediate host sampling. Environmental DNA (eDNA), defined by Thomsen and Willersley (2015) as "genetic material obtained directly from environmental samples (soil, sediment, water, etc.) without any obvious signs of biological source material," has the potential to be a powerful tool for evaluating the presence of microorganisms, of which direct observation is impossible, and for assessing biodiversity in aquatic environments.2 Furthermore, it has been shown that eDNA shed from fish is more highly concentrated in aquatic sediment than in water samples.3 In this study, we investigated the presence of eDNA in river sediment samples collected from areas affected by recent fire activity in Las Plumas National Forest, California, USA. Wildfires have been implicated as promoting environmental conditions suitable for the survival and success of myxozoan intermediate hosts by causing erosion of fine sediments into stream channels.4,5 Sediment samples were collected from 23 different watersheds during the fall of 2015. Extracted DNA from sediment samples (~ 10 g) was used as a template in a previously described TaqMan probe real-time PCR (qPCR) assay, specific for the detection of C. shasta.6 Four of the analyzed sediment samples were found to be positive for C. shasta. Future research will investigate the correlation of parasite eDNA with ceratomyxosis incidence in sentinel triploid rainbow trout (Oncorhynchus mykiss), intermediate host (Manayunkia speciosa) abundance estimated with qPCR, and C. shasta spores in the water column at a given location quantified using qPCR. With this information, we hope to validate the use of eDNA as a non-invasive, rapid, sensitive, and specific method for establishing risk of infection.
* Presenting author
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