THE GENETIC DIVERSITY AND EPIZOOTIOLOGY OF INFECTIOUS HEMATOPOIETIC NECROSIS VIRUS

Infectious hematopoietic necrosis virus (IHNV) is a rhabdovirus which causes a serious disease in salmonid fish. The T1 ribonuclease fingerp rinting method was used to compare the RNA genomes of 26 isolates of I HNV recovered from sockeye salmon (Oncorhynchus nerka), chinook salmon (O. tshawytscha), and steelhead trout (O. mykiss) throughout the enzo otic portion of western North America. Most of the isolates analyzed i n this study were from a single year (1987) to limit time of isolation as a source of genetic variation. In addition, isolates from differen t years collected at three sites were analyzed to investigate genetic drift or evolution of IHNV within specific locations. All of the isola tes examined by T1 fingerprint analysis contained less than a 50% vari ation in spot location and were represented by a single fingerprint gr oup. The observed variation was estimated to correspond to less than 5 % variation in the nucleic acid sequence. However, sufficient variatio n was detected to separate the isolates into four subgroups which appe ared to correlate to different geographic regions. Host species appear ed not to be a significant source of variation. The evolutionary and e pizootiologic significance of these findings and their relationship to other evidence of genetic variation in IHNV isolates are discussed.