Abstract
Scuticociliatosis is caused by facultative histophagous ciliated protozoa in the subclass Scuticociliatida of the phylum Ciliophora, and can cause fatal disease in teleosts fish species such as sea bass (Dicentrarchus labrax), Japanese flounder (Paralichthys olivaceous), olive flounder (Paralichthys olivaceus), turbot (Scophthalmus maximus), southern bluefin tuna (Thunnus maccoyii), and Syngnathidae (including seahorses and sea dragons).1,2,3,4 Although scuticociliate infection in elasmobranchs have been reported previously,5 the information is still limited. The present report describes an acute fatal scuticociliate infection in the central nervous system of a 2-year-old female zebra shark. The zebra shark showed poor appetite and lethargy on November 17, 2016. Next day, the animal was floating upside down and biting its own tail. Hematology and plasma biochemistry revealed decreased hematocrit (PCV=15%), decreased total white blood cell count (17.75 x 103/μL), increased albumin (1.5 g/dL), and increased creatine kinase (CPK=5259 U/L).6,7 Dexamethasone, ceftazidime, and B-complex were given, but the animal was found dead on the morning of November 19, 2016. Grossly, the brain showed a watery appearance with multifocal accumulation of white cloudy substance. There were multifocal ecchymotic hemorrhages on the liver surface. Microscopically, abundant granulocytes, including heterophils, eosinophils and neutrophils, infiltrated in the meninges and extended into the underlying grey matter with scattered macrophages. There were numerous approximately 20 to 25 μm in diameter, round to oval protozoan organisms with a hyperchromatic round to oval macronucleus (approximately 10 μm in diameter) and a variably vacuolated pale basophilic cytoplasm. Varying numbers of homogeneous eosinophilic intracytoplasmic droplets were found in these protozoan organisms, suggestive of erythrophagocytosis. In some regions of the meninges, the inflammation was mainly composed of abundant macrophages and lymphocytes. Necrohemorrhagic hepatitis and interstitial nephritis were noted without the presence of protozoan organisms. In addition, no protozoan organisms were found on the blood smear or in the lymphatic/blood vessels under histological examination. Protozoan species identification by PCR and DNA sequencing was performed, and the amplified amplicons was 100% identical to the corresponding gene fragment of Philasterides dicentrarchi (P. dicentrarchi). It is speculated the P. dicentrarchi invaded the animal via the nasal route or the ampullary system,8,9 and then directly entered the central nervous system.
Acknowledgements
The authors want to thank all the personnel of Farglory Ocean Park for sample collection and storage.
* Presenting author
+ Student presenter
References
1. Di Cicco E, Paradis E, Stephen C, Turba ME, Rossi G. 2013. Scuticociliatid ciliate outbreak in Australian potbellied seahorse, Hippocampus abdominalis (Lesson, 1827): clinical signs, histopathologic findings, and treatment with metronidazole. J Zoo Wildl Med. 44:435–440.
2. Jin CN, Harikrishnan R, Moon YG, Kim MC, Kim JS, Balasundaram C, Azad IS, Heo MS. 2009. Histopathological changes of Korea cultured olive flounder, Paralichthys olivaceus due to scuticociliatosis caused by histophagous scuticociliate, Philasterides dicentrarachi. Vet Parasitol. 161:292–301.
3. Puig L, Traveset R, Palenzuela O, Padros F. 2007. Histopathology of experimental scuticociliatosis in turbot Scophthalmus maximus. Dis Aquat Organ. 76:131–140.
4. Rossteuscher S, Wenker C, Jermann T, Wahli T, Oldenberg E, Schmidt-Posthaus H. 2008. Severe scuticociliate (Philasterides dicentrarchi) infection in a population of sea dragons (Phycodurus eques and Phyllopteryx taeniolatus). Vet Pathol. 45:546–550.
5. Stidworthy MF, Garner MM, Bradway DS, Westfall BD, Joseph B, Repetto S, Guglielmi E, Schmidt-Posthaus H, Thornton SM. 2014. Systemic scuticociliatosis (Philasterides dicentrarchi) in sharks. Vet Pathol. 51:628–632.
6. Haman KH, Norton TM, Thomas AC, Dove AD, Tseng F. 2012. Baseline health parameters and species comparisons among free-ranging Atlantic sharpnose (Rhizoprionodon terraenovae), bonnethead (Sphyrna tiburo), and spiny dogfish (Squalus acanthias) sharks in Georgia, Florida, and Washington, USA. J Wildl Dis. 48:295–306.
7. Otway NM. 2015. Serum biochemical reference intervals for free-living Sand Tiger sharks (Carcharias taurus) from east Australian waters. Vet Clin Pathol. 44:262–274.
8. Camus A, Berliner A, Clauss T, Hatcher N, Marancik D. 2013. Serratia marcescens associated ampullary system infection and septicaemia in a bonnethead shark, Sphyrna tiburo (L.). J Fish Dis. 36:891–895.
9. Harikrishnan R, Jin CN, Kim JS, Balasundaram C, Heo MS. 2012. Philasterides dicentrarchi, a histophagous ciliate causing scuticociliatosis in olive flounder, Philasterides dicentrarchi - histopathology investigations. Exp Parasitol. 130:239–245.