Severe Scuticociliate (Philasterides dicentrarchi) Infection in a Population of Sea Dragons (Phycodurus eques and Phyllopteryx taeniolatus)

Abstract

Scuticociliatosis is a disease of fish induced by ciliated parasites of the genus Scuticociliatida. It has been described in sea horses (Hippocampus sp.), flounders (Paralichthys olivaceus), and turbots (Scophthalmus maximus). Here we present a case study of a population of sea dragons chronically infected with scuticociliates identified as Philasterides dicentrarchi by histopathology and PCR. Beginning in 2004, over a period of 19 months, 10 sea dragons (Phycodurus eques and Phyllopteryx taeniolatus) were found dead in an aquarium of the Zoological Garden Basle, Switzerland. Clinically, the animals showed only faint symptoms of disease over a short period of time. At necropsy, macroscopic lesions were confined to the skin with multiple, often hemorrhagic, ulcerations. Histologically, epidermal ulcers were associated with necrosis and inflammation of the underlying dermis and musculature. Numerous ciliates, with a morphology consistent with scuticociliates, were present in these lesions. In several animals these ciliates had invaded blood vessels and were detected in gills and internal organs including kidney, thyroid gland, and central nervous system (CNS). In these organs, mild degenerative lesions and inflammatory reactions were evident. The ciliates were identified as Philasterides dicentrarchi based on small-subunit ribosomal RNA (SSUrRNA) gene sequences obtained by polymerase chain reaction (PCR) on DNA extracted from paraffin-embedded tissue sections. Our report shows that scuticociliate infections of sea dragons can develop into a systemic infection and that both species of sea dragons can be affected.