TABLE 4.

Effect of HA glycosylation and the length of NA stalk on infectivity and virulence in mice

VirusMLD50 (log10)aMID50 (log10)b
Short NALong NADifference (long NA − short NA)Short NALong NADifference (long NA − short NA)
486-none4.82c9.24.380.23.73.5
486-1316.27.321.121.461.45−0.1
486-1587.417.2−0.211.961.46−0.5
486-1695.53>7.0d>1.472.21.05−1.15
486-131/1696.2>7.7d>1.50.460.960.5
486-158/1696.77.120.421.21.66−0.46
486-131/158/1698.37>9.0d>0.633.262.26−1.0
  • a MLD50 was determined by inoculating groups of five mice with serial 10-fold dilutions of virus stock.

  • b MID50 was determined by inoculating groups of five mice with serial 10-fold dilutions of virus stock and by determining the presence of virus in lung at 3 days postinfection.

  • c MID50 and MLD50 titers were calculated by the method of Reed and Muench (18) and were expressed as the EID50 value corresponding to 1 MID50 or MLD50.

  • d Highest achievable dose for inoculation of mice due to reduced virus yields in culture.