Genetic and antigenic analysis of the first A/New Caledonia/20/99-like H1N1 influenza isolates reported in the Americas

Abstract

From February through May of 1999, 13 cases of Influenza A virus (FLUAV), type H1N1 were reported at a Department of Defense influenza surveillance sentinel site in Lima, Peru. Genetic and antigenic analysis by hemagglutination inhibition and direct nucleotide sequencing of the HA1 region of the hemagglutinin gene were performed on two isolates, A/Peru/1641/99 and A/Peru/1798/99. Both isolates were distinct from the Bayern/7/95-like viruses circulating in the Americas and closely related to a Beijing/262/95-like variant, A/New Caledonia/20/99. With the exception of travel-related cases, the detection of these isolates represents the first appearance of New Caledonia/20/99-like viruses in the Americas. Since the characterization of these Peru isolates, a number of New Caledonia/20/99-like viruses have been reported worldwide. For the 2000/01 and 2001/02 influenza seasons, the World Health Organization (WHO) has recommended the inclusion of A/New Caledonia/20/99 as the H1N1 vaccine component for both the southern and northern hemispheres.

Figure 1

The amino acid sequence of the HA1 region of the hemagglutinin of the Peru isolates and A/Beijing/262/95 compared with the 2000/01 and 2001/02 vaccine strain, A/New Caledonia/20/99. Amino acid numbering corresponds to H3 subtype , with additional amino acids residues present in the H1 subtype sequence indicated by an asterisk. Residue substitutions are show. A dot (.) indicates amino acid homology to A/New Caledonia/20/99.

Figure 2

An unrooted phylogenetic analysis of the HA1 gene nucleotide sequence of influenza A H1N1 viruses isolated since 1990. Peru isolates 1621 and 1798 are within the Beijing/262/95 lineage but are more similar to A/New Caledonia/20/99. A number of isolates characterized by Brooks Air Force Base from 1999 to 2001 were also A/NC/20/99-like. The tree was generated by using the Jotun-Hein algorithm in MegAlign software (version 3.18). Horizontal lines are proportional to the number of substitutions between branch points. Asterisk (*) denotes 2000/01 vaccine strain; (¹) denotes isolates characterized by Brooks Air Force Base. Brooks Air Force Base isolates are available from Genbank under accession numbers AF268312, AF268313 and AY029287-AY029292.