Genotypic varieties of La Crosse virus isolated from different geographic regions of the continental United States and evidence for a naturally occurring intertypic recombinant La Crosse virus.

The tripartite ribonucleic acid (RNA) genomes of 23 alternate isolates of La Crosse virus have been analyzed by the procedure of oligonucleotide fingerprinting. By comparison with the fingerprints of the three viral RNA species (large, medium and small) of prototype La Crosse virus, the viruses have been categorized in terms of the degree of their RNA sequence relatedness. The A type La Crosse viruses, which have been recovered from Wisconsin, Minnesota, Indiana and Ohio, have viral RNA sequences that are closely related to those of prototype La Crosse virus. The B type La Crosse viruses, which have been recovered from Minnesota, Wisconsin and Illinois, have RNA sequences which, although related, are easily distinguished from those of type A viruses. A La Crosse virus isolate obtained from Rochester, Minnesota, appears to be an intertypic type A/B recombinant, it has a small size RNA segment like those of the B type La Crosse virus isolates, but medium- and large-sized RNA species like those of the A type La Crosse virus isolates. The C type La Crosse viruses have viral RNA sequences that neither closely resemble the A or B type La Crosse viruses. They have been recovered from eastern Ohio, New York State, Texas, Georgia and North Carolina.