Optimization of inactivated H5N9 highly pathogenic avian influenza vaccine and inactivated Salmonella enterica serovar Typhimurium vaccine with antigen dose and prime-boost regimen in domestic ducks.

Owing to the increase in the number of diseases affecting ducks and the demand for food safety by consumers, vaccination has become one of the factors that influence duck meat productivity. The highly pathogenic avian influenza (HPAI) virus is one of the most prevalent and causes one of the most lethal diseases in domestic ducks, and Salmonella enterica serovar Typhimurium is a food-borne pathogen persistent in the domestic duck population. To better understand the optimal usage of HPAI and S. enterica serovar Typhimurium vaccines, we aimed to determine antigen dose, oil and gel adjuvant usage with prime-boost regimen, and vaccination age, inducing the best immune response in ducks, without an effect on body weight gain. In the case of the inactivated H5N9 vaccine, a single dose of vaccine was inadequate to induce proper antibody titer when administered to day-old ducks, which necessitates boost vaccination. Administration of the oil-adjuvanted H5N9 vaccine administration in day-old and 2-week-old ducks resulted in a lower body weight at the time of slaughtering, compared to that of gel-adjuvanted H5N9 vaccine. However, gel-adjuvanted H5N9 vaccine failed to induce proper immune response to an extent recommend by OIE-World Organization for Animal Health. In the case of the Salmonella enterica serovar Typhimurium vaccine, a moderate or low dose of vaccine was appropriate for day-old ducks receiving the gel prime-oil boost vaccination. Single vaccination with oil adjuvants affects the mean body weight of 7-week-old ducks, suggesting that the gel adjuvant is more suitable for meat production. We expect that the use of adjuvants in a prime-boost regimen and at antigen doses set in this study will be helpful to maximize body weight in the case of domestic duck production at the actual farm site.

Immune response in domestic ducks following intradermal delivery of inactivated vaccine against H5N1 highly pathogenic avian influenza virus adjuvanted with oligodeoxynucleotides containing CpG motifs.

Ducks are a natural reservoir for H5N1 highly pathogenic avian influenza (HPAI) viruses, which produces a range of clinical outcomes from asymptomatic infections to severe disease with mortality. Vaccination against HPAI is one of the few methods available for controlling avian influenza virus (AIV) infection in domestic ducks; therefore, it is necessary to improve vaccine efficacy against HPAI in domestic ducks. However, few studies have focused on enhancing the immune response by testing alternative administration routes and adjuvants. While attempting to maximize the efficacy of a vaccine, it is important to select an appropriate vaccine delivery route and adjuvant to elicit an enhanced immune response. Although several studies have indicated that the vaccination of ducks against HPAI viruses has offered protection against lethal virus challenge, the immunogenicity of the vaccine still requires improvement. In this study, we characterized the immune response following a novel vaccination strategy against H5N1 HPAI virus in domestic ducks. Our novel intradermal delivery system and the application of the cytosine-phosphodiester-guanine (CpG) oligodeoxynucleotide (ODN) adjuvant allowed us to obtain information regarding the sustained vaccine immunity. Compared with the intramuscular route of vaccination, the intradermal route resulted in higher antibody titer as well as lower antibody deviation following secondary vaccination. In addition, the use of a CpG-ODN adjuvant had a dose-sparing effect on antibody titer. Furthermore, when a high dose of antigen was used, the CpG-ODN-adjuvanted vaccine maintained a high mean antibody titer. This data demonstrates that intradermal immunization combined with administration of CpG-ODN as an adjuvant may be a promising strategy for improving vaccine efficacy in domestic ducks.