Table 1.

Pathogenicity of rBC, rLaSota, and rLaSota V.F. viruses in vivo

Virus	ICPI	IVPI
rBC	1.58	1.45
rLaSota	0.00	0.00
rLaSota V.F	1.12	0.00

The virulence of the viruses was evaluated by ICPI in day-old-chicks and IVPI in 6-week old chickens. ICPI was determined by inoculating 0.05 ml of a 1:10 dilution of fresh infective allantoic fluid of each virus into the brains of 10 1-day-old chicks. The birds were observed daily for 8 days and at each observation, scored 0 if normal, 1 if sick, and 2 if dead. The ICPI value is the mean score per bird per observation. Highly virulent viruses give values approaching two and avirulent viruses give values approaching 0. For IVPI, 0.1 ml of a 1:10 dilution of fresh infective allantoic fluid of wild type and mutant viruses, were inoculated into 6-week old chickens intra-nasally and intra-ocularly. The birds were observed for clinical symptoms and mortality, every 24 h for a period of 10 days and scored 0 if normal, 1 if sick, 2 if paralyzed and 3 if dead. The IVPI value is the mean score per bird per observation. Highly virulent viruses give values approaching three and avirulent viruses give values approaching 0.