The low efficiency of viral amplification may prevent etiology determinations, intensive surveillance of epidemiology and the tracing of potential natural domestic hosts for viral pathogens during an outbreak. For instance, avian metapneumovirus (MPV), which primarily attacks the respiratory tract, replicates inefficiently in embryonic eggs. Diagnosis of MPV infection is mainly dependent on the detection of viral RNA or viral antigens, but not viral isolation [5, 6] . In addition, to investigate the epidemiology of avian influenza viruses (AIV) requires efficient and sensitive viral detection and amplification system for comprehensive collection of the viruses from waterfowl and migratory birds [17, 31] . However, the wildbird isolated AIV are usually mildly or nonpathogenic to chicken embryos [20, 26] and the efficiency of viral isolation is often unsatisfactory in embryonated eggs [11, 19] .