Development of DIVA (differentiation of infected from vaccinated animals) vaccines utilizing heterologous NA and NS1 protein strategies for the control of triple reassortant H3N2 influenza in turkeys

Evaluation of an N1 NA antibody-specific enzyme-linked lectin assay for detection of H5N1 highly pathogenic avian influenza virus infection in vaccinated birds

Unprecedented H5N1 highly pathogenic avian influenza (HPAI) outbreaks are occurring around the world and there is growing interest in the use of vaccines in affected regions. Vaccination when properly applied can contribute to HPAI control by significantly reducing virus shedding and breaking the transmission chain, but it requires robust surveillance to ensure that international trade is not affected. Thus, it is imperative to establish a test to differentiate vaccinated only animals from vaccinated and then infected animals (DIVA). In this study, we applied enzyme-linked lectin assay (ELLA) to specifically detect N1 neuraminidase (NA) antibody by inhibition of NA activity and provide a proof-of-concept bench validation using reference and experimental serum samples. We used a wild-type low pathogenic H7N1 virus of North American lineage as the ELLA antigen. The NA inhibition ELLA (NI-ELLA) was evaluated for its specificity and sensitivity using reference and experimental samples. The results demonstrated that the NI-ELLA was highly specific with low background NI activity against influenza-negative sera from different species although varying level of cross-reactivity was observed against sera of different NA subtypes with highest cross-reactivity against N4 subtype sera. Using a conservative positive cut-off threshold of 50 % NI activity, NI-ELLA provides 100 % specificity with all reference sera of 9 different NA subtypes. The relative sensitivity of NI-ELLA was evaluated in detecting H5N1 infection in vaccinated and then challenged birds and NI-ELLA showed higher detection rate of H5N1 infection compared with commercial NP ELISAs and real-time RT-PCR. Overall, the NI-ELLA shows high specificity and sensitivity and has the potential for application in DIVA surveillance with further validation.

Efficacy of recombinant H5 vaccines delivered in ovo or day of age in commercial broilers against the 2015 U.S. H5N2 clade 2.3.4.4c highly pathogenic avian Influenza virus

BACKGROUND

Avian influenza is a highly contagious, agriculturally relevant disease that can severely affect the poultry industry and food supply. Eurasian-origin H5Nx highly pathogenic avian influenza viruses (HPAIV) (clade 2.3.4.4) have been circulating globally in wild birds with spill over into commercial poultry operations. The negative impact to commercial poultry renewed interest in the development of vaccines against these viruses to control outbreaks in the U.S.

METHODS

The efficacy of three recombinant H5 vaccines delivered in ovo or day of age were evaluated in commercial broilers challenged with the 2015 U.S. H5N2 clade 2.3.4.4c HPAIV. The recombinant vaccines included an alphavirus RNA particle vaccine (RP-H5), an inactivated reverse genetics-derived (RG-H5) and recombinant HVT vaccine (rHVT-AI) expressing H5 hemagglutinin (HA) genes. In the first experiment, in ovo vaccination with RP-H5 or rHVT-AI was tested against HPAI challenge at 3 or 6 weeks of age. In a second experiment, broilers were vaccinated at 1 day of age with a dose of either 107 or 108 RP-H5, or RG-H5 (512 HA units (HAU) per dose).

RESULTS

In experiment one, the RP-H5 provided no protection following in ovo application, and shedding titers were similar to sham vaccinated birds. However, when the RP-H5 was delivered in ovo with a boost at 3 weeks, 95% protection was demonstrated at 6 weeks of age. The rHVT-AI vaccine demonstrated 95 and 100% protection at 3 and 6 weeks of age, respectively, of challenged broilers with reduced virus shedding compared to sham vaccinated birds. Finally, when the RP-H5 and rHVT vaccines were co-administered at one day of age, 95% protection was demonstrated with challenge at either 3 or 6 weeks age. In the second experiment, the highest protection (92%) was observed in the 108 RP-H5 vaccinated group. Significant reductions (p < 0.05) in virus shedding were observed in groups of vaccinated birds that were protected from challenge. The RG-H5 provided 62% protection from challenge. In all groups of surviving birds, antibody titers increased following challenge.

CONCLUSIONS

Overall, these results demonstrated several strategies that could be considered to protected broiler chickens during a H5 HPAI challenge.

Efficacy of inactivated and RNA particle vaccines against a North American Clade 2.3.4.4b H5 highly pathogenic avian influenza virus in chickens

Highly pathogenic avian influenza virus (HPAIV) has caused widespread outbreaks in poultry in the Americas. Because of the duration and extent of these outbreaks, vaccine use may be an additional tool to limit virus spread. Three vaccines were evaluated for efficacy in chickens against a current North American clade 2.3.4.4b H5 HPAIV isolate, A/turkey/Indiana/3703-003/2022 H5N1. The vaccines included: 1) a commercial inactivated reverse genetics (rg) generated H5N1 product with a clade 2.3.4.4c H5 hemagglutinin (HA) (rgH5N1); 2) a commercial alphavirus RNA particle (RP) vaccine with the TK/IN/22 HA; and 3) an in-house inactivated rg produced vaccine with the TK/IN/22 HA and a North American lineage N9 neuraminidase (NA) (SEP-22-N9). Both inactivated vaccines were produced with HA genes that were modified to be low pathogenic and with the remaining genes from the PR8 influenza strain. All vaccines provided 100% protection against mortality and morbidity and all vaccines reduced virus shed by the oropharyngeal and cloacal routes significantly compared to sham vaccinates. However, differences were observed among the vaccines in quantities of virus shed at two- and four-days post challenge (DPC). To determine if infected birds could be identified after vaccination to aid surveillance programs, serum was collected from the RP and SEP-22-N9 vaccine groups at 7, 10, and 14 DPC to detect antibody to the NA and nucleoprotein (NP) of the challenge virus by enzyme linked lectin assay (ELLA) and ELISA. As early as 7DPC ELLA detected antibody in sera from 100% of the chickens in the RP vaccinated group and 70% of the chickens in the SEP-22-N9 vaccinated group. Antibody to the NP was detected by commercial ELISA in more than 50% of the birds in the RP vaccinated group at each time point.

Development of an Inactivated H7N9 Subtype Avian Influenza Serological DIVA Vaccine Using the Chimeric HA Epitope Approach

H7N9 avian influenza virus (AIV) is an emerging zoonotic pathogen, and it is necessary to develop a differentiating infected from vaccinated animals (DIVA) vaccine for the purpose of eradication. H7N9 subtype AIV hemagglutinin subunit 2 glycoprotein (HA2) peptide chips and antisera of different AIV subtypes were used to screen H7N9 AIV-specific epitopes. A selected specific epitope in the HA2 protein of H7N9 AIV strain A/Chicken/Huadong/JD/17 (JD/17) was replaced with an epitope from an H3N2 subtype AIV strain by reverse genetics. The protection and serological DIVA characteristics of the recombinant H7N9 AIV strain were evaluated. The results showed that a specific epitope on the HA2 protein of H7N9 AIV, named the H7-12 peptide, was successfully screened. The recombinant H7N9 AIV with a modified epitope in the HA2 protein was rescued and named A/Chicken/Huadong/JD-cHA/17 (JD-cHA/17). The HA titer of JD-cHA/17 was 10 log₂, and the 50% egg infective dose (EID₅₀) titer was 9.67 log₁₀ EID₅₀/ml. Inactivated JD-cHA/17 induced a hemagglutination inhibition (HI) antibody titer similar that of the parent strain and provided 100% protection against high-pathogenicity or low-pathogenicity H7N9 AIV challenge. A peptide chip coated with H7-12 peptide was successfully applied to detect the seroconversion of chickens infected or vaccinated with JD/17, while there was no reactivity with antisera of chickens vaccinated with JD-cHA/17. Therefore, the marked vaccine candidate JD-cHA/17 can be used as a DIVA vaccine against H7N9 avian influenza when combined with an H7-12 peptide chip, making it a useful tool for stamping out the H7N9 AIV.

IMPORTANCE DIVA vaccine is a useful tool for eradicating avian influenza, especially for highly pathogenic avian influenza. Several different DIVA strategies have been proposed for avian influenza inactivated whole-virus vaccine, involving the neuraminidase (NA), nonstructural protein 1 (NS1), matrix protein 2 ectodomain (M2e), or HA2 gene. However, virus reassortment, residual protein in a vaccine component, or reduced vaccine protection may limit the application of these DIVA strategies. Here, we constructed a novel chimeric H7N9 AIV, JD-cHA/17, that expressed the entire HA protein with substitution of an H3 AIV epitope in HA2. The chimeric H7N9 recombinant vaccine provides full clinical protection against high-pathogenicity or low-pathogenicity H7N9 AIV challenge. Combined with a short-peptide-based microarray chip containing the H7N9 AIV epitope in HA2, our finding is expected to be useful as a marker vaccine designed for avian influenza.

Avian Influenza Virus and DIVA Strategies

Vaccination is becoming a more acceptable option in the effort to eradicate avian influenza viruses (AIV) from commercial poultry, especially in countries where AIV is endemic. The main concern surrounding this option has been the inability of the conventional serological tests to differentiate antibodies produced due to vaccination from antibodies produced in response to virus infection. In attempts to address this issue, at least six strategies have been formulated, aiming to differentiate infected from vaccinated animals (DIVA), namely (i) sentinel birds, (ii) subunit vaccine, (iii) heterologous neuraminidase (NA), (iv) nonstructural 1 (NS1) protein, (v) matrix 2 ectodomain (M2e) protein, and (vi) haemagglutinin subunit 2 (HA2) glycoprotein. This short review briefly discusses the strengths and limitations of these DIVA strategies, together with the feasibility and practicality of the options as a part of the surveillance program directed toward the eventual eradication of AIV from poultry in countries where highly pathogenic avian influenza is endemic.

Neuraminidase gene homology contributes to the protective activity of influenza vaccines prepared from the influenza virus library

Whole-virus (WV) vaccines from influenza A/duck/Hokkaido/77 (H3N2), and its reassortant strains H3N4, H3N5 and H3N7, which have the same haemagglutinin (HA) gene but different neuraminidase (NA) genes, were prepared from our influenza virus library. Mice were intranasally immunized with equivalent doses of each vaccine (1-0.01 µg per mouse). All of the mice that received the highest dose of each vaccine (1 µg per mouse) showed equivalent high HA-inhibiting (HI) antibody titres and survived the H3N2 challenge viruses. However, mice that received lower doses of vaccine (0.1 or 0.01 µg per mouse) containing a heterologous NA had lower survival rates than those given the H3N2-based vaccine. The lungs of mice challenged with H3N2 virus showed a significantly higher virus clearance rate when the vaccine contained the homologous NA (N2) versus a heterologous NA, suggesting that NA contributed to the protection, especially when the HI antibody level was low. These results suggested that, even if vaccines prepared for a possible upcoming pandemic do not induce sufficient HI antibodies, WV vaccines can still be effective through other matched proteins such as NA.

DIVA vaccination strategies for avian influenza virus

Vaccination for both low pathogenicity avian influenza and highly pathogenic avian influenza is commonly used by countries that have become endemic for avian influenza virus, but stamping-out policies are still common for countries with recently introduced disease. Stamping-out policies of euthanatizing infected and at-risk flocks has been an effective control tool, but it comes at a high social and economic cost. Efforts to identify alternative ways to respond to outbreaks without widespread stamping out has become a goal for organizations like the World Organisation for Animal Health. A major issue with vaccination for avian influenza is trade considerations because countries that vaccinate are often considered to be endemic for the disease and they typically lose their export markets. Primarily as a tool to promote trade, the concept of DIVA (differentiate infected from vaccinated animals) has been considered for avian influenza, but the goal for trade is to differentiate vaccinated and not-infected from vaccinated and infected animals because trading partners are unwilling to accept infected birds. Several different strategies have been investigated for a DIVA strategy, but each has advantages and disadvantages. A review of current knowledge on the research and implementation of the DIVA strategy will be discussed with possible ways to implement this strategy in the field. The increased desire for a workable DIVA strategy may lead to one of these ideas moving from the experimental to the practical.