A recombinant Newcastle disease virus (NDV) expressing H6 hemagglutinin (HA) of a low pathogenic avian influenza virus (LPAIV) was generated by reverse genetics (NDVH6). The H6 open reading frame was inserted as an additional transcription unit between the fusion and hemagglutinin-neuraminidase (HN) gene of lentogenic NDV clone 30. Expression of the foreign gene was demonstrated by northern blot, western blot, and indirect immunofluorescence analyses. The protective efficacy against Newcastle disease and avian influenza of subtype H6 was evaluated in 3-wk-old chickens and turkeys. A single vaccination protected specific-pathogen-free (SPF) chickens against a subsequent lethal NDV infection and prevented shedding of AIV after homologous H6 LPAIV infection. Furthermore, vaccinated and AIV-infected animals could be differentiated by detection of AIV nucleoprotein-specific antibodies. Three-week-old commercial turkeys, exhibiting NDV-specific maternal antibodies, were partially protected against a lethal NDV challenge infection. The mortality rate of NDVH6-immunized turkeys was reduced to 40% compared to 90% in unvaccinated birds. After H6 LPAIV infection, shedding in NDVH6-immunized turkeys was only marginally reduced compared to NDV-immunized control birds. We previously described HA-expressing NDV recombinants as potent bivalent vaccines against Newcastle disease and highly pathogenic avian influenza of subtype H5 or H7. The results presented here are in contrast to the high protective efficacy in SPF chickens, as a single vaccination with NDVH6 was insufficient in turkeys in the presence of maternal antibodies against NDV. Therefore, the vector virus has to be improved to overcome these limitations.
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Vol. 55 • No. 2