Evaluation of the immune effect of a triple vaccine composed of fowl adenovirus serotype 4 fiber-2 recombinant subunit, inactivated avian influenza (H9N2) vaccine, and Newcastle disease vaccine against respective pathogenic virus challenge in chickens

Fowl adenovirus (FAdV), Avian influenza (AI), and Newcastle disease (ND) are prominent viral infectious diseases that pose a significant threat to the global poultry industry, resulting in substantial economic loss. To mitigate the occurrence of hydropericardium syndrome (HPS), a triple vaccine was developed by combining the nanoparticle-like fibre-2 protein with the inactivated H9N2 AI virus antigen derived from the A/chicken/Shandong/SZ/2008 strain, as well as the inactivated Newcastle disease virus (NDV) antigen obtained from the N7a strain, which was rescued from the NDV strain PLK-N-06. This particular strain was isolated during a chicken outbreak of ND and identified as velogenic. The immunological effect was evaluated by specific pathogen-free chicken challenge test. There was no significant difference in the specific antibody level in specific pathogen-free chickens between the triple vaccine and the monovalent vaccine (P > 0.05), which was significantly higher than that of the control group (P < 0.0001). The protective effect of triple vaccine against the 3 viruses could reach 100% after being challenged. No obvious lesions of FAdV, AI, or ND were observed in the target tissues and organs of the triple vaccine immunization group. Viral shedding test results showed that no three kinds of viruses were detected in larynx and cloaca on the fifth day after challenge. In conclusion, the immune protection effect against the 3 pathogens does not interfere with each other and can provide complete protection. The triple vaccine can be used as a candidate vaccine to prevent chickens from the three kinds of diseases, has high clinical application value, and can produce greater economic benefits.