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Diseases of Aquatic Organisms

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DAO 76:99-111 (2007)  -  doi:10.3354/dao076099

Mortality event in freshwater drum Aplodinotus grunniens from Lake Ontario, Canada, associated with viral haemorrhagic septicemia virus, Type IV

J. S. Lumsden1,*, B. Morrison2, C. Yason3, S. Russell1, K. Young1, A. Yazdanpanah1, P. Huber1, L. Al-Hussinee1, D. Stone4, K. Way4

1Fish Pathology Laboratory, Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario N1G 2W1, Canada
2Ontario Ministry of Natural Resources, Lake Ontario Management Unit, Glenora Fisheries Station, RR#4 Picton, Ontario KOK 2Y0, Canada
3Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Prince Edward Island C1A 4P3, Canada
4CEFAS Weymouth Laboratory, Barrack Rd., The Nothe, Weymouth, Dorset DT4 8UB, UK

ABSTRACT: A mortality event primarily affecting freshwater drum Aplodinotus grunniens was noted during April and May 2005 in the Bay of Quinte, Lake Ontario, Canada. A conservative estimate of the number of dead drum was approximately 100 metric tonnes. Large numbers of dead round goby Neogobius melanostomus were also seen, as well as a few muskellunge Esox masquinongy. In the drum, there was a consistent histological pattern of variably severe panvasculitis, a necrotising myocarditis, meningoencephalitis and a segmental enteritis. Moderate numbers of bullet-shaped viral particles consistent with a rhabdovirus were identified by transmission electron microscopy (TEM) in affected heart tissue. Following primary isolation from pooled tissues on fathead minnow (FHM) cells, a morphologically similar virus, ~165 × 60 nm in size, was visualised. Identification of the isolate as viral haemorrhagic septicemia virus (VHSV) was confirmed by enzyme immunoassay and by polymerase chain reaction. An appropriately sized product (468 bp) of the G-glycoprotein gene (nucleotides [nt] 340 to 807) was generated with RNA extracted from FHM cell supernatant. Analysis of a 360 nt partial glycoprotein gene sequence (nt 360 to 720) indicated a 96.4 to 97.2% nucleotide identity with known strains of North American (NA) VHSV. Analysis using Neighbour-joining distance methods assigned the isolate to the same lineage as the NA and Japanese isolates (Genogroup IV). However, there was sufficient sequence divergence from known NA VHSV isolates to suggest that this isolate may represent a distinct subgroup. The effects of ongoing mortality in freshwater drum and in multiple species during spring 2006 suggest that this newly recognised virus in the Great Lakes will have continued impact in the near future.

KEY WORDS: Freshwater drum · Aplodinotus grunniens · Viral haemorrhagic septicemia virus · VHSV · Genogroup IV · Vasculitis · Meningoencephalitis · Necrotising myocarditis · Enteritis

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