1999 Workshop Abstracts | Virus Evolution Home Page | Plant Biology Home Page

Molecular characterization of human influenza A viruses bearing swine-like hemagglutinin genes

Lynn Cooper, Christopher Olsen, Xiyan Xu,
Alexander Klimov, Nancy Cox,and Kanta Subbarao
Influenza Branch, Centers for Disease Control and Prevention, Atlanta, Georgia and
Department of Pathobiological Sciences, University of Wisconsin, Madison, Wisconsin.

In recent decades, sporadic cases of humans becoming infected with classical swine influenza A viruses in recent decades have generally not resulted in further human-to-human spread of these viruses. Although relatively rare, one concern about such infections is the possibility of genetic reassortment between human and swine influenza viruses, as well as with avian influenza viruses, which can infect pigs. We characterized the genomes of six influenza A viruses that were isolated from humans between 1990 and 1998, that were identified as swine influenza A viruses based on hemagglutination inhibition tests. Genotyping of the NS, M, NP, PB1, PB2, PA, and NA genes for each human isolate was initially based on specific restriction fragment length polymorphism (RFLP) patterns within portions of each gene segment, and the RFLP results were confirmed by sequence analysis. The RFLP patterns for genes of the first five viruses, isolated from 1990 to 1995, matched those of representative influenza A viruses isolated from pigs. Each gene was closely related to those of classical H1N1 swine viruses with no evidence of genetic reassortment between swine and human influenza A viruses. In contrast, the 1998 isolate, A/Wisconsin/10/98, had an unusual RFLP pattern on initial genotyping. Further analysis revealed that it was a reassortant that contained a mixture of swine, human, and avian influenza A virus genes. The HA, NA, NP, M and NS genes were related to genes from the classical swine H1N1 lineage. However, of the polymerase genes, PA and PB2 were related to avian virus genes and PB1 was related to human influenza virus genes. Reassortant viruses with human influenza A H3 and N2 surface glycoproteins and internal protein genes of swine, avian and human influenza A viruses were recently isolated in the US from multiple outbreaks of respiratory disease in pigs. The genotype of A/Wisconsin/10/98 provides further evidence for reassortment between avian, human and swine influenza A viruses and demonstrates that such reassortant viruses can infect humans. At this time, the epidemiologic consequences of this gene constellation on the transmission potential of such a virus for pigs and humans remain unknown.

Abstract - Presented at the Virus Evolution Workshop
Ardmore, OK
October 21 - 24th, 1999

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e-mail: mroossinck@noble.org

Dr. Marilyn Roossinck
Plant Biology Division
The Noble Foundation
P.O. Box 2180
Ardmore, OK 73402

phone: 580 224-6630