TABLE 1.
Pathogenicity of the HN cytoplasmic tail mutant viruses in embryonated eggs and chicks
| Virus | MDT (h)a | ICPIb |
|---|---|---|
| rBC | 58 | 1.49 |
| rBC/HNΔ2 | 59 | 1.51 |
| rBC/HNΔ4 | 50 | 1.61 |
| rBC/HNS6A | 51 | 1.58 |
| rBC/HNS6E | 62 | 1.41 |
a
The mean time (in hours) for the minimum lethal dose of virus to kill all the inoculated embryos. NDV strains were classified by the following criteria: virulent strains take <60 h to kill embryos, intermediate virulent strains take 60 to 90 h to kill embryos, and avirulent strains take >90 h to kill embryos.
b
Pathogenicity of NDV in 1-day-old SPF chicks was evaluated by the ICPI value: virulent strains had ICPI values of 1.5 to 2.0, intermediate virulent strains had ICPI values of 1.0 to 1.5, and avirulent strains had ICPI values of 0.0 to 0.5.