Table 1. Pathogenicity of the parental and recombinant viruses.
| Virus | MDT (h)a | ICPI scoreb |
|---|---|---|
| NDV-SG10-HN571 | 42.0 | 1.95 |
| rNDV-SG10-HN571 | 42.0 | 1.93 |
| rNDV-SG10-HN567 | 40.8 | 1.94 |
| rNDV-SG10-HN568 | 42.0 | 1.93 |
| rNDV-SG10-HN569 | 43.5 | 1.94 |
| rNDV-SG10-HN570 | 39.0 | 1.95 |
| rNDV-SG10-HN577 | 40.8 | 1.91 |
| rNDV-SG10-HN582 | 40.0 | 1.99 |
| rNDV-SG10-HN616 | 43.2 | 2.00 |
aMDT, the mean death times (hour) in embryonated chicken eggs. Criteria for classifying the virulence of NDVs: virulent viruses, <60 h; moderately virulent viruses, 60–90 h; avirulent viruses, >90 h.
bICPI, intracerebral pathogenicity index, determined by inoculating groups of 10 1-day-old SPF chicks with fresh infective allantoic fluid via the intracerebral route. The birds were observed for clinical symptoms and mortality daily for 8 days. At each observation, the birds were scored 0 if normal, 1 if sick, and 2 if dead. The ICPI is the mean score per bird per observation. Criteria for classifying the virulence of NDVs: virulent viruses, 1.5–2.0; moderately virulent viruses, 0.7–1.5; avirulent viruses, 0.0–0.7.