Histopathology analysis of APMV-infected 2-week-old chickens showed that infection by each of the APMVs, including APMV-5, produced tracheitis and mild pathology that was mainly restricted to the respiratory tract. Previous study with serologic assays in chickens infected with APMVs demonstrated a good humoral response on 14 dpi [39] . Thus, the birds indeed appeared to be infected even thought the recovery of infectious virus was often sporadic and low. A single APMV type, namely APMV-5, was not detected by virus isolation or by immunohistochemistry in any of the chickens in this study. However, the serologic assay of chickens that had been inoculated with APMV-5 also showed the development of virus specific antibodies detected by virus plaque reduction neutralization assay [39] , suggesting that infection had occurred. This suggests a low level of virus replication in chickens. Thus, although APMV-5 bears a furin cleavage site and can cause 100% mortality in budgerigars [25] , it was completely avirulent and replicated inefficiently in chickens. This is suggestive of a host range difference that was not greatly ameliorated by the presence of a multi-basic cleavage site.