ISOLATES OF VIRAL HEMORRHAGIC SEPTICEMIA VIRUS FROM NORTH-AMERICA AND EUROPE CAN BE DETECTED AND DISTINGUISHED BY DNA PROBES

Biotinylated DNA probes were constructed to hybridize with specific sequences within the messenger RNA (mRNA) of the nucleoprotein (N) gene of viral hemorrhagic septicemia virus (VHSV) reference strains from Europe (07-71) and North America (Makah). Probes were synthesized that were complementary to: (1) a 29-nucleotide sequence near the center of the N gene common to both the 07-71 and Makah reference strains of the virus; (2) a unique 28-nucleotide sequence that followed the open reading frame of the Makah N gene mRNA, most of which was absent in the 07-71 strain; and (3) a 22-nucleotide sequence within the 07-71 N gene that had 6 mismatches with the Makah strain. Sixteen diverse isolates of VHSV from North America and Europe were tested by dot blot hybridization. The first probe reacted with all isolates of the virus, the second probe reacted with only the North American isolates (including those from Pacific cod), and the third probe reacted with only the European isolates, including those from rainbow trout, brown trout and Atlantic cod. The probes did not react with mRNA extracted from uninfected cells or from cells infected with infectious hematopoietic necrosis virus (IHNV), a related fish rhabdovirus. The results showed that VHSV isolates from North America and Europe formed 2 genetically distinct strains of the virus in which isolates from different years or species of fish on each continent were more related to each other than to, isolates from the other continent. The results of this and other studies indicate that the North American strain of VHSV is enzootic in the North Pacific Ocean and is not a result of a recent importation of fish from Europe. When used in conjunction with a biotinylated probe that recognizes all isolates of IHNV, these reagents promise to simplify the detection of salmonid rhabdoviruses.