Herpesvirus salmonis: pathological changes in parenterally-infected rainbow trout, Salmo gairdneri Richardson, fry

After fry of rainbow trout, Salmo gairdneri Richardson, had been infected parenterally with Herpesvirus salmonis, moribund or freshly dead specimens were examined histopathologically. The virus produced a generalized infection, the first signs of which appeared after 2–3 weeks. Visceral and respiratory organs and the heart showed major pathological changes, and pancreatic syncytia were judged to be pathognomonic. Kidneys were prime targets for the virus and showed the highest levels of infectivity; lesser amounts of virus were present in the stomach, liver, and intestine. The virus did not spread by contact to produce clinical disease nor could disease or viral replication be induced by parenteral inoculation of yearling Oncorhynchus nerka (Walbaum).