Since several of the specific APMV strains under evaluation (i.e., APMV-4, -6, and -9) were isolated from other avian species including the mallard duck (see Table 1 ), their replication and pathogenicity were further evaluated in groups of 3-week-old ducks following intranasal inoculation. No clinical signs of illnesses in any of the infected groups were found up to 10 dpi. Three birds from each group were sacrificed on 4 dpi and the tissues were harvested for virus titration. None of the APMVs were detected in any of the tested tissues from any of the ducks by virus titration in DF1 cells (data not shown). However, APMVs were detected in some of the samples of trachea, lung, and spleens by inoculation into 9-day-old embryonated chicken eggs, although none of the APMVs (including APMV-1) were detected in any of the brain samples (Table 3 ; APMV-5 was not evaluated). APMV-1 strains BC and LaSota were the only APMVs that were detected in all three ducks in their respective groups, although replication was mostly restricted to the trachea. APMV-2 was found only in the trachea of a single duck, in contrast to its more efficient replication in chickens. APMV-3 was not detected in any samples from any duck, in contrast to its efficient replication and neurotropism in chickens. APMV-8 and -9 also were not detected in any duck. The other serotypes (APMV-4, -6, and -7) were each detected in the trachea of two ducks from its group, and in the lungs of one or two ducks from its group. APMV-4 replicated slightly better in ducks than in chickens. APMV-7 was the only serotype detected in the spleen (of a single duck), whereas it had not been detected in the spleen of infected chickens. Thus, the pattern of infection in chickens and ducks was substantially different and could not be predicted by the isolation history.