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

Biotinylated DNA probes were constructed to hybridize with specific se quences within the messenger RNA (mRNA) of the nucleoprotein (N) gene of viral hemorrhagic septicemia virus (VHSV) reference strains from Eu rope (07-71) and North America (Makah). Probes were synthesized that w ere 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 rea ding frame of the Makah N gene mRNA, most of which was absent in the 0 7-71 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 hybridiz ation. The first probe reacted with all isolates of the virus, the sec ond probe reacted with only the North American isolates (including tho se from Pacific cod), and the third probe reacted with only the Europe an isolates, including those from rainbow trout, brown trout and Atlan tic cod. The probes did not react with mRNA extracted from uninfected cells or from cells infected with infectious hematopoietic necrosis vi rus (IHNV), a related fish rhabdovirus. The results showed that VHSV i solates from North America and Europe formed 2 genetically distinct st rains of the virus in which isolates from different years or species o f fish on each continent were more related to each other than to, isol ates from the other continent. The results of this and other studies i ndicate that the North American strain of VHSV is enzootic in the Nort h Pacific Ocean and is not a result of a recent importation of fish fr om Europe. When used in conjunction with a biotinylated probe that rec ognizes all isolates of IHNV, these reagents promise to simplify the d etection of salmonid rhabdoviruses.