ISOLATION OF THE CAUSAL VIRUS OF INFECTIOUS SALMON ANEMIA (ISA) IN A LONG-TERM CELL-LINE FROM ATLANTIC SALMON HEAD KIDNEY

long-term cell line (SHK-1) supporting replication of the causal virus of infectious salmon anaemia (ISA) has been established. The cell lin e was developed from a culture of Atlantic salmon (Salmo salar L.) hea d kidney cells. CPE was observed in SHK-1 cells 12-14 days after inocu lation with ISA-infective tissue material. The time for CPE to develop decreased after repeated passages of medium from infected cell cultur es to new cultures. Transmission trials demonstrated that Atlantic sal mon parr developed ISA after intraperitoneal injection of preparations made from infected cells and growth medium. The ISA infectivity of th e cell preparations increased with incubation time of inoculated cells . Cell cultures in a second passage were found to have a higher infect ivity than the primary inoculated cultures. Virus particles with a dia meter of approximately 100-120 nm, and which contained an external env elope and granules were seen in electron micrographs of thin sections of infected cells. Most of the virus particles were located extracellu larly close to the cell surface, and in some cases, a connection betwe en virus and plasma membrane could be observed. This indicates that vi rus particles were released by budding. Enveloped virus particles of 4 5-140 nm in diameter were seen in abundance in electron micrographs of a negatively stained purified virus preparation. Large, highly pleomo rphic particles up to 700 nm in the longest dimension were occasionall y observed in unpurified preparations. The evidence is therefore stron g that the virus isolated in SHK-1 cells is the aetiological agent of ISA.