DAO 23:189-199 (1995)  -  doi:10.3354/dao023189

An anti-infectious hematopoietic necrosis virus (IHNV) nucleoprotein monoclonal antibody, 1NDW14D (IgG₁), labeled with a streptavidin gold marker was utilized to monitor infection of juvenile rainbow trout and coho salmon with IHNV at the ultrastructural level. Juvenile fish were challenged with a virulent isolate of IHNV or mock-challenged with phosphate buffered saline. In both juvenile rainbow trout and coho salmon, the target area for infection by IHNV appeared to be the esophageal/cardiac stomach region (ECSR), particularly the mucus-secreting serous cardiac glands (MSSG). We previously found that, at the light microscopic and ultrastructural levels in rainbow trout, the MSSG form long continuous glands in association with the esophageal mucosa located opposite the swimbladder pneumatic duct. In contrast, the coho salmon MSSG bud from the esophageal mucosa, forming dense bodies located posterior to the pneumatic duct. With the aid of a 20 nm immunogold marker labeling the nucleoprotein of the virus, the progression of the infection was followed from the esophageal mucosa to the MSSG in both species. The immunogold marker was located in both the rainbow and coho salmon epithelial cells, which exhibited severe intercellular edema with separation of the mucosa at 24 h post challenge. The immunogold marker was also found in the MSSG of both species, with the rainbow trout exhibiting glandular cystic degeneration as early as 1 h post challenge, which further developed to a severe cystic degeneration by 24 h. The coho salmon exhibited a similar but milder reaction to the virus. In both species, the 24 h post mock-challenged MSSG exhibited no morphological changes. When the infection was monitored in the MSSG of both rainbow trout and coho salmon at 1 and 24 h post viral challenge, a statistically significant difference between the 2 time points was detected within each fish species, suggesting that replication occurred in the MSSG. In addition, a statistically significant difference was detected between fish species at both 1 and 24 h, indicating quantitatively that the virus is replicated more efficiently in the MSSG of rainbow trout than in the MSSG of coho salmon.

Rhabdovirus . Portal of entry . Mucus-secreting cardiac glands (MSSG) . Rainbow trout . Coho Salmon