Pathotyping
Intracerebral pathogenicity index (ICPI) was determined following
European guidelines (CEC, 1992). Ten
one-day-old SPF chickens were inoculated intracerebrally with 0.05 ml of
10-1 diluted virus stock (HA > 32) and
examined daily for 8 days. The ICPI is calculated by scoring each bird
every day from 0 (normal), 1 (sick) and to 2 (dead). Based on this score
NDV-isolates are considered lentogenic (-0.7), mesogenic
(>0,7-1.3) or velogenic (>1,5)
(Alexander, 1998). Animal experiments were
carried out in accordance with the legally approved protocol (MV-LALLF-
/7221.3-1.1-030/13). Specific pathogen free White leghorn chickens
purchased from Lohmann Animal Health, Cuxhaven, Germany, were raised in
isolation units at FLI until age of inoculation. Infection and
immunization experiments were performed in in separated cages at animal
biosafety level-3 (BSL-3). Feed and water were provided daily.