Table 1.

Characteristics and mouse pathogenicity phenotypes of influenza A H5N1 viruses isolated from humans

H5N1 virusOriginCase outcomePassage historyaAntigenic groupbAmino acids in HA1cMouse LD50dMouse pathogenicity phenotypee
Age (yr)Sex
HK/481/972MaleRecoveredE2ANXA101.7 High
HK/483/9713FemaleMVf; diedC1E3BNXT102.4 High
HK/485/9724FemaleMV; recoveredC2E2BNXS102.9 High
HK/491/974MaleRecoveredC1E2BNXS102.0 High
HK/503/971MaleRecoveredC1E2BNXS102.0 High
HK/514/9725FemaleMV; diedCXE2BNXS<101.5 High
HK/516/9760FemaleMV; diedC2E2ANXA<101.5 High
HK/532/9714FemaleRecoveredCXE2BNXT<101.5 High
HK/542/9719FemaleMV; recoveredCXE3BNXS<101.5 High
HK/156/973MaleMV; diedE3ANXA105.9 Intermediate
HK/486/975FemaleRecoveredC2E3ANXA>106.5 Low
HK/488/972MaleRecoveredC1E4ANXA>106.5 Low
HK/507/973FemaleRecoveredC1E2ANXA>106.5 Low
HK/538/973MaleRecoveredCXE3ANXA>106.5 Low
HK/97/9834FemaleMV; diedCXE4ANXA>106.5 Low
  • a Number of passages in a given host cell type: C, MDCK cells; E, embryonated eggs; X, unknown.

  • b As defined in Bender et al. (3).

  • c HA residues 154 to 156 encode a potential glycosylation site defined by NXS/T, where X is not proline. GenBank accession numbers for H5 HA sequences are AF036356 (30),AF046096-97 (27), and AF102671-82 (3).

  • d LD50s were determined by inoculating groups of five lightly anesthetized mice intranasally with 106.5 to 101.5 EID50 of virus in a volume of 50 μl. Mice were checked daily for 14 days, and the LD50s were calculated as previously described (17). LD50s are expressed as the EID50 corresponding to 1 LD50.

  • e Viruses with an LD50 of >106.5 were considered to be of low pathogenicity, and viruses with an LD50 of <103.0 were considered to be of high pathogenicity.

  • f MV, mechanical ventilation required.