Table 1.
Properties of 7:1 recombinant and parental influenza viruses used in this study
| Virus stock* | Stock titer, pfu/ml | Weight loss, %† | LD50‡ |
|---|---|---|---|
| 1918 | 4.5 × 107 | 22.8 | 3.25 |
| Tx PA:1918 | 7.8 × 107 | 20.8 | 3.5 |
| Tx PB1:1918 | 1.2 × 108 | 10.5 | 5.5 |
| Tx PB2:1918 | 1.8 × 107 | 18.1 | 3.75 |
| Tx HA:1918 | 4.6 × 107 | 7.3 | >6 |
| Tx NP:1918 | 1.9 × 107 | 22.5 | 3.5 |
| Tx NA:1918 | 3.0 × 107 | 15.3 | 5.5 |
| Tx M:1918 | 2.1 × 107 | 20.2 | 3.5 |
| Tx NS:1918 | 8.8 × 108 | 18.5 | 3.25 |
| Tx/91 | 2.1 × 108 | 3.7 | >6 |
*Prepared on MDCK cells with trypsin and incubated for 48–72 h.
†Maximum percent weight loss (mean of six mice per group) after infection with 105 pfu of virus.
‡Expressed as the log10 pfu required to give 1 LD50.