Generation and evaluation of a Newcastle disease virus-based H9 avian influenza live vaccine

Infection with H9 avian influenza virus (AIV) and Newcastle disease virus (NDV) are two important causes of egg drop in layer and breeder poultry, leading to severe economic loss in the industry. Currently in China, inactivated H9 AIV vaccine and live attenuated NDV vaccine have to be repeatedly administered to prevent egg drop in layer animals. Using reverse genetics, we constructed a recombinant NDV expressing an H9 AIV hemagglutinin (HA) from an H9N2 field isolate, A/Chicken/ Shandong/2/2007. The HA gene was inserted into the intergenic region between the phosphoprotein (P) and matrix (M) genes of the LaSota NDV vaccine strain. The recombinant virus stably expressing the HA gene, rL-H9, was found to be innocuous after intracerebral inoculation of 1-day-old chickens. A single dose of 10(6) 50% egg infectious dose of the recombinant virus intranasally inoculated into chickens induced high levels of NDV- and AIV H9-specific hemagglutination-inhibition antibody. Complete protection from clinical disease and mortality against challenge with a lethal dose of velogenic NDV was observed in chickens and 90% of chickens were protected from clinical disease, mortality, and virus shedding against challenge with homologous H9N2 AIV. Our results suggest that recombinant NDV is suitable as a potential bivalent live attenuated vaccine against both NDV and H9 AIV infection in poultry.