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Diseases of Aquatic Organisms

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DAO 139:189-197 (2020)  -  DOI: https://doi.org/10.3354/dao03481

Advanced vacuolation indicates propagation of various salmonid alphavirus type 2 isolates in Acholeplasma-infected BF-2 cells

O. Schachner1,*, N. Dinhopl2, A. Friedl1, H. Soliman1, M. El-Matbouli1

1Clinical Division of Fish Medicine, University of Veterinary Medicine, 1210 Vienna, Austria
2Institute of Pathology, University of Veterinary Medicine, 1210 Vienna, Austria
*Corresponding author:

ABSTRACT: During previous routine inspections of bluegill fry (BF-2) and rainbow trout gonad (RTG-2) cells incubated with organ samples from asymptomatic Arctic char Salvelinus alpinus, brook trout Salvelinus fontinalis, and rainbow trout Oncorhynchus mykiss, a distinctive, reproducible cytopathic effect (CPE) appeared. The striking CPE, involving progressive vacuolation turning into slowly proceeding pyknotic degeneration, was originally attributed exclusively to enhanced growth of Acholeplasma sp. However, at a recent re-examination of re-infected BF-2 cells using electron microscopy (EM), conventional PCR, and quantitative PCR (qPCR), a virus was also detected. Two days post inoculation (dpi), EM revealed characteristic virions inside cytoplasmic vacuoles and next to bacteria outside the cells. The nucleotide sequences of the viral nsP3 gene fragment obtained from supernatants of infected cells were 100% identical and representative for salmonid alphavirus type 2 (SAV 2). The 16S RNA gene (16S rDNA) fragment sequences of the Mollicutes-specific PCR product obtained from SAV-infected as well as virus-free BF-2 control cells were identical with Acholeplasma laidlawii. In addition, qPCR results indicated enhanced propagation of virus and bacteria increasing with vacuolation between 5 and 8 dpi. Advanced vacuolation can be regarded as a CPE of both SAV and A. laidlawii, suggesting a viral impact on the bacterial infection that turns a latent intracellular stage into an apparent degenerative condition.


KEY WORDS: Sleeping disease virus · SDV · Brook trout · Salvelinus spp. · Rainbow trout · Vacuolation · Mycoplasma sp. · Cell line susceptibility


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Cite this article as: Schachner O, Dinhopl N, Friedl A, Soliman H, El-Matbouli M (2020) Advanced vacuolation indicates propagation of various salmonid alphavirus type 2 isolates in Acholeplasma-infected BF-2 cells. Dis Aquat Org 139:189-197. https://doi.org/10.3354/dao03481

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