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United States Department of Agriculture

Agricultural Research Service

Title: Negligible Risk Associated with the Movement of Processed Rainbow Trout from An Infectious Hematopoietic Necrosis Virus (Ihnv) Endemic Area

Authors
item Lapatra, S. - CLEAR SPRINGS FOODS,INC
item Batts, W. - WESTERN FISHERIES RES
item OVERTURF, KENNETH
item Jones, G. - CLEAR SPRINGS FOODS, INC
item Shewmaker, W. - CLEAR SPRINGS FOODS, INC
item Winton, J. - WESTERN FISHERIES RES

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 2001
Publication Date: July 1, 2001

Interpretive Summary: Infectious hematopoietic necrosis virus (IHNV) is a rhabdovirus causing epidemics among wild and cultured salmonid fish. The virus is endemic to western portions of North America including the commercial rainbow trout, Oncorhynchus mykiss, used in the aquaculture industry in southern Idaho, USA. The objective of this study was to analyze the risk of IHNV transmission associated with the movement of processed rainbow trout from an area endemic for IHNV to areas where IHNV has been previously undetected. To determine the contamination potential of animals that had become infected with IHNV and survived, we injected fish with IHNV and performed weekly analysis on fish that survived the infection. We detected only 1 animal that still retained the presence of IHNV that survived the infection and that animal came from the initial week of testing survivors. During the next 8 weeks, no virus was detected in any of surviving fish when examined by both tissue culture and molecular techniques. To further assess the risk associated with the movement of processed rainbow trout from an IHNV endemic area, we examined the records of a major trout producer and determined that during the last 7 years, not one record of IHNV introduction into a nonendemic area, to which this product was shipped, was ever reported. These results provide new scientific information that further substantiate the negligible risk associated with the movement of processed rainbow trout from an IHNV endemic area.

Technical Abstract: To assess the risk associated with processed rainbow trout produced in an area endemic for infectious hematopoietic necrosis virus (IHNV), fish with typical IHNV deformities were tested for viral presence. Tissue samples in the area of the deformity were collected, as well as brain and kidney tissue from each fish. Nested reverse transcription-PCR for the detection of IHNV used the glycoprotein (G) gene. All samples were negative for IHNV by virus isolation and nested RT-PCR. To assess virus clearance, pathogen-free rainbow trout were either injected with IHNV or sham infected. In the first study 33% of the infected fish died. Ten days after the last mortality or 34 days post-infection, 6 fish from each treatment were sacrificed weekly for 6 weeks. Tissue homogenates from individual fish were tested by virus isolation and nested Rt-PCR using the nucleoprotein N gene. All tissue homogenates were negative for IHNV. When this study was repeated, 54% of the infected fish died and beginning 34 days post- infection was positive for virus, however, all remaining tissue specimens were negative. A strong humoral response was detected in the IHN survivors in both studies that suggested a mechanism responsible for virus clearance. These results provide scientific information that can be used to assess the risk associated with the movement of processed rainbow trout from an IHNV endemic area.

Last Modified: 9/10/2014
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