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Diseases of Aquatic Organisms

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DAO 68:17-28 (2005)  -  doi:10.3354/dao068017

Histological, serological and virulence studies on rainbow trout experimentally infected with recombinant infectious hematopoietic necrosis viruses

Alejandro Romero1, Antonio Figueras1, Carolina Tafalla1, Maria-Isabel Thoulouze2, Michel Bremont2, Beatriz Novoa1,*

1Instituto de Investigaciones Marinas, Consejo Superior de Investigaciones Cientificas (CSIC), Eduardo Cabello 6, 36208 Vigo, Spain
2Unité de Virologie et Immunologie Moléculaires, Centre de Recherche de Jouy-en-Josas, Institut National de la Recherche Agronomique (INRA), 78352 Jouy-en-Josas Cedex, France
*Corresponding author. Email:

ABSTRACT: Several recombinant infectious hematopoietic necrosis viruses (IHNV) were produced by reverse genetics and their pathogenicity in trout was evaluated and compared to that of the wild type (wt) viruses IHNV and viral haemorrhagic septicemia virus (VHSV). Recombinant IHNVs used in this study were: rIHNV, identical to the wtIHNV; rIHNV-Gvhsv, a recombinant virus expressing the VHSV G gene instead of the IHNV G gene; rIHNV-Gmut, which possesses 2 targeted mutations in the glycoprotein; and rIHNVmut-Gmut, which is similar to the rIHNV-Gmut, but exhibits additional mutations along the genome. Results obtained in experimental infections showed that the rIHNV and rIHNV-Gmut were the most virulent recombinant viruses. Severity of the lesions induced by the different recombinant viruses was in agreement with mortality data. The kidney and the liver were the organs most affected by the most pathogenic viruses, and the lesions observed resembled those produced by wtIHNV. The introduction of mutations did not alter the tissue tropism of the virus. The recombinant viruses were able to replicate in fish, as shown by immunoperoxidase assay and RT-PCR. Antibodies against IHNV were detected in the fish inoculated with IHNV, rIHNV, rIHNV-Gmut and rIHNVmut-Gmut, and antibodies against VHSV were also found in fish infected with rIHNV-Gvhsv. Finally, antibody production was highest in fish infected with the rIHNVmut-Gmut even though this virus was the least virulent.

KEY WORDS: Rhabdovirus · Infectious hematopoietic necrosis virus · IHNV · Viral hemorrhagic septicemia virus · VHSV · Oncorhynchus mykiss · Reverse genetics · Recombinant virus

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