“The North American strain of Tetracapsuloides bryosalmonae utilises the salmonid Oncorhynchus mykiss and bryozoan Fredericella indica (7369)”

The North American strain of Tetracapsuloides bryosalmonae utilises the salmonid Oncorhynchus mykiss and bryozoan Fredericella indica

In Europe, the myxozoan parasite responsible for Proliferative Kidney Disease (PKD), Tetracapsuloides bryosalmonae (T. bryo), cycles between salmonid fishes and freshwater bryozoans. However, in North America no active hosts (species that shed viable, infectious spores) have been identified. To assess the active host status of steelhead trout Oncorhynchus mykiss and the bryozoan Fredericella indica, we conducted fish-to-bryozoan and bryozoan-to-fish transmission experiments. Specific-pathogen-free F. indica colonies were first exposed to effluent from naturally infected O. mykiss and monitored weekly using stereomicroscopy for overt T.bryo infections. Malacospores from infected colonies were then introduced to naïve O. mykiss, which were held at 16°C and sampled for PCR and histology at 2 and 8 wks post-exposure. Additionally, to investigate vertical transmission of T.bryo, statoblasts and hatched zooids from overtly infected F. indica colonies were screened with stereomicroscopy and qPCR. We observed the development of overt infections in exposed F. indica, indicating that subclinically-infected O. mykiss shed viable fish malacospores of the NA strain of T. bryo. Sequentially, malacospores shed from the bryozoan induced clinical PKD in naive O. mykiss; extrasporogonic stages of the parasite were observed in histology, and T. bryo DNA was detected. We found no evidence of vertical transmission within F. indica. Given that O. mykiss is widely reared and stocked across North America, these findings highlight the importance of pre-release surveillance in susceptible stocks to prevent dissemination of T. bryo into habitats where infected, active host populations may overlap.

1. Das, Nilanjana, Oregon State University, Author
2. Atkinson, Stephen, Oregon State University, Author
3. Hallett, Sascha, Oregon State University, Presenter