The emergence of epitheliocystis in the upper Rhone region: evidence for Chlamydiae in wild and farmed salmonid populations
We present the first study comparing epitheliocystis in a wild and farmed salmonid in Europe. Sampling three tributaries to the Lake Geneva, including one from headwaters to river mouth, revealed an unequal distribution of epitheliocystis in brown trout (Salmo trutta). When evaluated histologically and comparing sites grouped as wild versus farm, the probability of finding infected trout is higher on farms. In contrast, the infection intensities, as estimated by the number of cysts per gill arch, were higher on average and showed maximum values in the wild trout. Sequence analysis showed the most common epitheliocystis agents were Candidatus Piscichlamydia salmonis, all clustering into a single clade, whereas Candidatus Clavichlamydia salmonicola sequences cluster in two closely related subspecies, of which one was mostly found in farmed fish and the other exclusively in wild brown trout, indicating that farms are unlikely to be the source of infections in wild trout. A detailed morphological analysis of cysts using transmission electron microscopy revealed unique features illustrating the wide divergence existing between Ca. P. salmonis and Ca. C. salmonicola within the phylum Chlamydiae.
KeywordsBrown trout Candidatus Piscichlamydia salmonis Candidatus Clavichlamydia salmonicola River Farm
We thank the fish farmers at the Venoge who provided the brown trout for examination. Further we thank Aurelie Rubin and the team of the Centre for Fish and Wildlife Health, Bern for help during the sampling. This study was partly financed by the ESKAS-Bundesstipendien für ausländische Studierende, Kunstschaffende und Forschende, Bern, Switzerland.
Compliance with ethical standards
Conflict of interest
The authors declare they have no competing interests and they were notified about the content of the manuscript.
Animal rights statement
All animals were treated according to the Swiss welfare regulations (permission number: 2871).
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