Replication of parental and F protein cleavage site mutant APMV-4 viruses in 3-week-old ducks.

aGroups of 3-week-old ducks were inoculated with each virus by the combined intranasal and intratracheal routes. Three birds from each group were sacrificed, and tissues samples (brain, trachea, lung, and spleen) were collected on 4 dpi and homogenized. To confirm the virus replication, aliquots (100 µl each) of the collected samples were inoculated into three eggs, and allantoic fluids were collected on 3 dpi. Virus replication was determined by hemagglutination assay.