Virulence of Infectious hematopoietic necrosis virus and Infectious pancreatic necrosis virus coinfection in rainbow trout (Oncorhynchus mykiss) and nucleotide sequence analysis of the IHNV glycoprotein gene

The outcomes of a coinfection of rainbow trout (Oncorhynchus mykiss) with Infectious hematopoietic necrosis virus (IHNV) strain S46 and Infectious pancreatic necrosis virus (IPNV) strain S46 was determined after waterborne infection. Trout infected with the IHNV/IPNV.S46 sample, (a mixed sample containing equal infectious titers of the viruses) showed 50% less mortality than fish infected with either of the reference viruses alone. Forty-five days after the coinfection, IPNV antigens were detected by flow cytometry in 49 to 63% of the leukocytes from the surviving trout; whereas, only 9-15.6% of the leukocytes expressed IHNV viral antigens. IPNV was easily detected by reverse transcription-polymerase chain reaction (RT-PCR), whereas, for IHNV, a second step of amplification of a 753 bp fragment corresponding to the internal sequences of the IHNV G gene was necessary to optimize viral detection. The sequence of the IHNV gene involved in virulence, the glycoprotein (G) gene, was determined for the IHNV.S46 and compared with other sequences available in the GenBank. Changes found were not located in the antigenic domains of the glycoprotein and were considered not significant.