RESUMO
Four H5N2 experimental vaccine strains and the apathogenic wild duck H5N3 influenza virus A/duck/ Moscow/4182/2010 (dk/4182) were tested as a live poultry vaccine. Experimental strains had the hemagglutinin of the A/Vietnam/1203/04 strain lacking the polybasic HA cleavage site or the hemagglutinin from attenuated virus (Ku/ at) that was derived from the highly pathogenic influenza virus A/chicken/Kurgan/3/2005 (H5N1). The hemagglutinin of the Ku-at has the amino acid substitutions Asp54/Asn and Lys222/Thr in HA1 and Val48/Ile and Lys131/Thr in HA2, while maintaining the polybasic HA cleavage site at an invariable level. The other genes of these experimental strains were from the H2N2 cold-adapted master strain A/Leningrad/134/17/57 (VN-Len and Ku-Len) or from the apathogenic H6N2 virus A/gull/Moscow/3100/2006 (VN-Gull and Ku-Gull). A single immunization of mice with all tested strains elicited a high level of serum antibodies and provided complete protection against the challenge with the lethal dose of A/chicken/Kurgan/3/05. The pathogenicity indexes of the Ku-at and the other strains for chicken were virtually zero, whereas the index of the parent H5N1 virus A/chicken/Kurgan/3/2005 was 2.98. Intravenous, intranasal, and aerosol routes of vaccination were compared. It was shown that the strain dk/4182 was totally apathogenic for one-day-old chicken and provided complete protection against the highly pathogenic H5N1 virus.