Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2007
Publication Date: 10/12/2007
Citation: Spackman, E., Swayne, D.E., Suarez, D.L., Senne, D.A., Pedersen, J.C., Killian, M.L., Pasick, J., Handel, K., Pillai, S.P., Lee, C., Stallknecht, D., Slemons, R., Ip, H.S., Deliberto, T. 2007. Characterization of low- pathogenicity H5N1 avian influenza viruses from North America. Journal of Virology. 81(21):11612-11619. Interpretive Summary: Avian influenza viruses of the H5 and N1 subtype were collected from wild birds in North America and characterized. Genetic features of the virus coat proteins, the hemagglutinin (HA) and neuraminidase (NA), were evaluated. Selected recent isolates were tested for their ability to infect and cause disease in chickens, and for their ability to transmit among chickens, turkeys, and ducks. Finally, characteristics of the H5 coat proteins which could be used to identify candidate isolates for use as vaccine strains were assessed. It was shown that the North American H5N1 viruses are duck adapted viruses, they did not cause disease in any species tested, and had genetic features consistent with wild bird viruses. The North American H5N1 viruses are distinct genetically and biologically from the Asian highly pathogenic H5N1 viruses. The characterization of the H5 coat protein revealed a high level of variation among North American viruses, but the North American viruses were more closely related to each other than with European or Asian viruses. This data supports earlier data that showed that quality vaccines made with North American viruses could protect poultry against European and Asian H5 strains.
Technical Abstract: Wild bird surveillance in North America for avian influenza (AI) viruses with a goal of early identification of the Asian H5N1 highly pathogenic AI virus has identified at least six low pathogenic H5N1 AI viruses between 2004 and 2006. The hemagglutinin (HA) and neuraminidase (NA) genes from all 6 H5N1 viruses and an additional 38 North American wild bird-origin H5 subtype and 28 N1 subtype viruses, were sequenced and compared with sequence available from GenBank by phylogenetic analysis. Both the HA and NA were phylogenetically distinct from viruses from outside of North America, and from viruses recovered from mammals. Four of the H5N1 AI viruses were characterized as low pathogenicity by standard in vivo pathotyping tests. One of the H5N1 viruses, A/MuteSwan/MI/451072-2/06, was shown to replicate to low titers in chickens, turkeys, and ducks. However, transmission of A/MuteSwan/MI/451072-2/06 was more efficient among ducks than chickens or turkeys based on virus shed. The 50% chicken infectious dose for A/MuteSwan/MI/451072-2/06, and three other wild waterfowl origin H5 viruses were also determined and were between 10log5.3 and 10log7.5 50% egg infectious doses. Finally, seven H5 viruses, representing different phylogenetic clades were evaluated for their antigenic relatedness by hemagglutination inhibition assay, showing the antigenic relatedness was largely associated with geographic origin. Overall the data supports the conclusion that North American H5 wild bird origin AI viruses are low pathogenicity, wild bird adapted viruses, and are antigenically and genetically distinct from the highly pathogenic Asian H5N1 virus lineage.