Antigenic characterization of highly pathogenic avian influenza A(H5N1) viruses with chicken and ferret antisera reveals clade-dependent variation in hemagglutination inhibition profiles

Identification and analysis of B cell epitopes of hemagglutinin of H1N1 influenza virus

The frequent variation of influenza virus hemagglutinin (HA) antigen is the main cause of influenza pandemic. Therefore, the study of B cell epitopes of HA is of great significance in the prevention and control of influenza virus. In this study, the split vaccine of 2009 H1N1 influenza virus was used as immunogen, and the monoclonal antibodies (mAbs) were prepared by conventional hybridoma fusion and screening techniques. The characteristics of mAbs were identified by ELISA method, Western-blot test and hemagglutination inhibition test (HI). Using the obtained mAbs as a tool, the B cell epitopes of HA were predicted by ELISA blocking test, sandwich ELISA method and computer simulation method. Finally, four mAbs against HA antigen of H1N1 influenza virus were obtained. The results of ELISA and computer prediction showed that there were at least two types of epitopes on HA of influenza virus. The results of this study complemented the existing methods for predicting HA epitopes, and also provided a new method for predicting other pathogenic microorganisms.

Efficacy of two vaccines against recent emergent antigenic variants of clade 2.3.2.1a highly pathogenic avian influenza viruses in Bangladesh

H5N1 highly pathogenic avian influenza viruses (HPAIVs) have caused outbreaks in poultry in Bangladesh since 2007. While clade 2.2.2 and 2.3.4.2 HPAIVs have not been detected since 2012, clade 2.3.2.1a viruses have caused continuous outbreaks since 2012 despite the use of vaccines. In this study, we evaluated the efficacy of two H5 vaccines licensed in Bangladesh, RE-6 inactivated vaccine, and a recombinant herpesvirus of turkeys vaccine with an H5 insert (rHVT-H5), for protection against recent field viruses in chickens. We selected three viruses for efficacy tests (A/chicken/Bangladesh/NRL-AI-3237/2017, A/crow/Bangladesh/NRL-AI-8471/2017 and A/chicken/Bangladesh/NRL-AI-8323/2017) from 36 H5 viruses isolated from Bangladesh between 2016 and 2018 by comparing the amino acid sequences at five antigenic sites (A-E) and analyzing hemagglutination inhibition (HI) titers with reference antisera. The RE-6 and rHVT-H5 vaccines both conferred 80-100% clinical protection (i.e. reduced morbidity and mortality) against the three challenge viruses with no significant differences in protection. In addition, both vaccines significantly decreased viral shedding from infected chickens as compared to challenge control chickens. Based on these metrics, the current licensed H5 vaccines protected chickens against the recent field viruses. However, the A/crow/Bangladesh/NRL-AI-8471/2017 virus exhibited antigenic divergence including: several unique amino acid changes in antigenic epitope sites A and B and was a serological outlier in cross HI tests as visualized on the antigenic map. The continuing emergence of such antigenic variants which could alter the dominant antigenicity of field viruses should be continuously monitored and vaccines should be updated if field efficacy declines.

Cross-Protection by Inactivated H5 Prepandemic Vaccine Seed Strains against Diverse Goose/Guangdong Lineage H5N1 Highly Pathogenic Avian Influenza Viruses

The highly pathogenic avian influenza virus (HPAIV) H5N1 A/goose/Guangdong/1996 lineage (Gs/GD) is endemic in poultry across several countries in the world and has caused sporadic lethal infections in humans. Vaccines are important in HPAIV control both for poultry and in prepandemic preparedness for humans. This study assessed inactivated prepandemic vaccine strains in a One Health framework across human and agricultural and wildlife animal health, focusing on the genetic and antigenic diversity of field H5N1 Gs/GD viruses from the agricultural sector and assessing cross-protection in a chicken challenge model. Nearly half (47.92%) of the 48 combinations of vaccine and challenge viruses examined had bird protection of 80% or above. Most vaccinated groups had prolonged mean death times (MDT), and the virus-shedding titers were significantly lower than those of the sham-vaccinated group (P ≤ 0.05). The antibody titers in the prechallenge sera were not predictive of protection. Although vaccinated birds had higher titers of hemagglutination-inhibiting (HI) antibodies against the homologous vaccine antigen, most of them also had lower or no antibody titer against the challenge antigen. The comparison of all parameters and homologous or closely related vaccine and challenge viruses gave the best prediction of protection. Through additional analysis, we identified a pattern of epitope substitutions in the hemagglutinin (HA) of each challenge virus that impacted protection, regardless of the vaccine used. These changes were situated in the antigenic sites and/or reported epitopes associated with virus escape from antibody neutralization. As a result, this study highlights virus diversity, immune response complexity, and the importance of strain selection for vaccine development to control H5N1 HPAIV in the agricultural sector and for human prepandemic preparedness. We suggest that the engineering of specific antigenic sites can improve the immunogenicity of H5 vaccines.IMPORTANCE The sustained circulation of highly pathogenic avian influenza virus (HPAIV) H5N1 A/goose/Guangdong/1996 (Gs/GD) lineage in the agricultural sector and some wild birds has led to the evolution and selection of distinct viral lineages involved in escape from vaccine protection. Our results using inactivated vaccine candidates from the human pandemic preparedness program in a chicken challenge model identified critical antigenic conformational epitopes on H5 hemagglutinin (HA) from different clades that were associated with antibody recognition and escape. Even though other investigators have reported epitope mapping in the H5 HA, much of this information pertains to epitopes reactive to mouse antibodies. Our findings validate changes in antigenic epitopes of HA associated with virus escape from antibody neutralization in chickens, which has direct relevance to field protection and virus evolution. Therefore, knowledge of these immunodominant regions is essential to proactively develop diagnostic tests, improve surveillance platforms to monitor AIV outbreaks, and design more efficient and broad-spectrum agricultural and human prepandemic vaccines.

Vertical transmission of ALV from ALV-J positive parents caused severe immunosuppression and significantly reduced marek's disease vaccine efficacy in three-yellow chickens

In order to evaluate the influence of the vertical transmission of avian leukosis virus (ALV) from J subgroup (ALV-J) positive parents on the vaccine efficacy of Marek's disease virus (MDV), ALV-J positive male breeders × female breeders of Three-yellow chickens and the ALV negative male breeder × the negative female breeders were used respectively for crossbreeding to produce eggs and the hatching offspring. The commercial CVI988/Rispens vaccine was used to vaccinate the crossbred offspring at 1-day-old. At 7-days-old, the birds were inoculated with the inactivated oil-emulsion vaccines (OEVs) AIV-H5 monovalent and NDV + AIV-H9 bivalent, respectively. Then the birds were challenged with a Chinese very virulent (vv) MDV field strain GXY2 at 14-day-old. The results showed that the viral load of the challenged GXY2 in the offspring from the ALV-J positive breeders was significantly higher than that from the ALV-negative breeders' (P < 0.05), and the mortality and tumor incidence of offspring from the ALV-J positive breeders were higher than those of the ALV-negative breeders. Also the offspring of the ALV-J positive breeders exhibited a significant negative effect on the development of the immune organs (P < 0.05) and lower antibody responses to the vaccinations with the commercial OEVs (P<0.05). The MD vaccine protective index in the offspring from the ALV-J positive breeders was lower than that from the ALV-negative breeders. The results of the study demonstrated that the vertical transmission of ALV from the ALV-J positive parents caused severe immunosuppression and significantly reduced the Marek's disease vaccine efficacy in Three-yellow chickens.

A systematic study towards evolutionary and epidemiological dynamics of currently predominant H5 highly pathogenic avian influenza viruses in Vietnam

This study aimed to elucidate virus, host and environmental dynamics of Vietnamese H5 highly pathogenic avian influenza viruses (HPAIVs) during 2014–2017. Epidemiologically, H5 HPAIVs were frequently detected in apparently healthy domestic and Muscovy ducks and therefore these are preferred species for H5 HPAIV detection in active surveillance. Virologically, clade 2.3.2.1c and 2.3.4.4 H5 HPAIVs were predominant and exhibited distinct phylogeographic evolution. Clade 2.3.2.1c viruses clustered phylogenetically in North, Central and South regions, whilst clade 2.3.4.4 viruses only detected in North and Central regions formed small groups. These viruses underwent diverse reassortment with existence of at least 12 genotypes and retained typical avian-specific motifs. These H5 HPAIVs exhibited large antigenic distance from progenitor viruses and commercial vaccines currently used in poultry. Bayesian phylodynamic analysis inferred that clade 2.3.2.1c viruses detected during 2014–2017 were likely descended from homologous clade viruses imported to Vietnam previously and/or preexisting Chinese viruses during 2012–2013. Vietnamese clade 2.3.4.4 viruses closely shared genetic traits with contemporary foreign spillovers, suggesting that there existed multiple transboundary virus dispersals to Vietnam. This study provides insights into the evolution of Vietnamese H5 HPAIVs and highlights the necessity of strengthening control measures such as, preventive surveillance and poultry vaccination.