Tetracapsuloides bryosalmonae is a myxozoan parasite of freshwater bryozoans and salmonids, causing proliferative kidney disease in the latter. To date, detection of the parasite has required collection of hosts and subsequent molecular or histological examination. The release of infectious spores from both hosts offers an opportunity to detect the parasite in water samples. We developed a novel SYBR® Green quantitative real-time PCR (qPCR) assay for T. bryosalmonae in water samples which provides an estimation of bryozoan malacospore numbers and tested the assay in 3 rivers in southern England (UK) over a period of 5 wk. The assay proved to be both highly sensitive and specific to the parasite, detecting low levels of spores throughout the study period. Larger-volume samples afforded greater detection likelihood, but did not increase the number of spores detected, possibly as a result of low and patchy spore distributions and lack of within-site replication of large-volume samples. Based on point-measurements, temperature was positively associated with the likelihood of detecting spores, possibly reflecting the temperature dependence of spore shedding from bryozoan hosts. The presence of T. bryosalmonae in water samples was predominantly influenced by spatial (sites within rivers, amongst rivers) and temporal (sampling dates) factors, while the latter also influenced quantification cycle (Cq) values and spore abundance. Environmental monitoring for infectious stages can complement traditional methods, providing faster and easier detection and avoiding potentially prolonged searching, collecting and destructive sampling of invertebrate and vertebrate hosts.
We are thankful to Darren Butterworth (Trafalgar Fisheries [River Avon]), Robert Starr (Hungerford Fishery [River Dun]), Mrs. Rochienne Pearce and Winchester College (River Itchen) for access to collecting sites. We also thank all field assistants based at the Natural History Museum (Brian Smith, Laetitia Gunton, Alex Gruhl, Graihagh Hardinge, Jahcub Trew) and Nick Taylor (Centre for Environment, Fisheries & Aquatic Sciences [Cefas]) and Chris Williams (Environment Agency [EA]) for their support for research on assessing the risk of PKD. We thank Sascha Hallett (Oregon State University) for initial advice on techniques. The research was funded by the Natural Environment Research Council (NE/019227/1), the EA and Cefas. I.F. was also funded by the Fundação para a Ciência e a Tecnologia (SFRH/BD/86118/2012) and Pescanova SA. H.H.
was fun ded by the Swiss National Science Foundation Sinergia project CRSII3_147649.
- Proliferative kidney disease
- Environmental DNA
- Disease risk