A two dose immunization with an inactivated reassortant H5N2 virus protects chickens against lethal challenge with homologous 2.3.2.1 clade and heterologous 2.2 clade highly pathogenic avian influenza H5N1 viruses

A single immunization with H5N1 virus-like particle vaccine protects chickens against divergent H5N1 influenza viruses and vaccine efficacy is determined by adjuvant and dosage

The H5N1 subtype highly pathogenic avian influenza virus (HPAIV) reveals high variability and threatens poultry production and public health. To prevent the spread of H5N1 HPAIV, we developed an H5N1 virus-like particle (VLP) vaccine based on the insect cell-baculovirus expression system. Single immunization of the H5N1 VLP vaccines induced high levels of HI antibody titres and provided effective protection against homologous virus challenge comparable to the commercial inactivated vaccine. Meanwhile, we assessed the relative efficacy of different adjuvants by carrying out a head-to-head comparison of the adjuvants ISA 201 and ISA 71 and evaluated whether the two adjuvants could induce broadly protective immunity. The ISA 71 adjuvanted vaccine induced significantly higher levels of Th1 and Th2 immune responses and provided superior cross-protection against antigenically divergent H5N1 virus challenge than the ISA 201 adjuvanted vaccine. Importantly, increasing the vaccine dose could further enhance the cross-protective efficacy of H5N1 VLP vaccine and confer completely sterilizing protection against antigenically divergent H5N1 virus challenge, which was mediated by neutralizing antibodies. Our results suggest that the H5N1 VLP vaccine can provide broad-spectrum protection against divergent H5N1 influenza viruses as determined by adjuvant and vaccine dose.

Rational approach to vaccination against highly pathogenic avian influenza in Nigeria: a scientific perspective and global best practice

Since 2006, highly pathogenic avian influenza (HPAI) subtypes H5Nx have adversely affected poultry production in Nigeria. Successive waves of infections in the last two decades have raised concerns about the ability to contain infections by biosecurity alone, and evidence of recurrent outbreaks suggests a need for adoption of additional control measures such as vaccination. Although vaccination can be used to control virus spread and reduce the morbidity and mortality caused by HPAI, no country using vaccination alone as a control measure against HPAI has been able to eliminate or prevent re-infection. To inform policy in Nigeria, we examined the intricacies of HPAI vaccination, government regulations, and scientific data regarding what kind of vaccines can be used based on subtype, whether inactivated or live attenuated should be used, when to deliver vaccine either proactively or reactively, where to apply vaccination either in disease control zones, regionally, or nationally, and how to vaccinate the targeted poultry population for optimum success. A resurgence of HPAI outbreaks in Nigeria since 2018, after the country was declared free of the epidemic following the first outbreak in 2006, has led to enhanced intervention. Controlled vaccination entails monitoring the application of vaccines, the capacity to differentiate vaccinated from infected (DIVA) flocks, and assessing seroconversion or other immune correlates of protection. Concurrent surveillance for circulating avian influenza virus (AIV) and analyzing AIV isolates obtained via surveillance efforts for genetic and/or antigenic mismatch with vaccine strains are also important. Countries with high investment in commercial poultry farms like Nigeria may identify and zone territories where vaccines can be applied. This may include ring vaccination to control HPAI in areas or production systems at risk of infection. Before adoption of vaccination as an additional control measure on commercial poultry farms, two outcomes must be considered. First, vaccination is an admission of endemicity. Secondly, vaccinated flocks may no longer be made accessible to international poultry markets in accordance with WOAH trade regulations. Vaccination must therefore be approached with utmost caution and be guided by science-based evidence throughout the implementation strategy after thorough risk assessment. Influenza vaccine research, development, and controlled application in addition to biosecurity may be a precautionary measure in the evolving HPAI scenario in Nigeria.

The Origin of Internal Genes Contributes to the Replication and Transmission Fitness of H7N9 Avian Influenza Virus

H9N2 avian influenza viruses (AIVs) have donated internal gene segments during the emergence of zoonotic AIVs, including H7N9. We used reverse genetics to generate A/Anhui/1/13 (H7N9) and three reassortant viruses (2:6 H7N9) which contained the hemagglutinin and neuraminidase from Anhui/13 (H7N9) and the six internal gene segments from H9N2 AIVs belonging to (i) G1 subgroup 2, (ii) G1 subgroup 3, or (iii) BJ94 lineages, enzootic in different regions throughout Asia. Infection of chickens with the 2:6 H7N9 containing G1-like H9N2 internal genes conferred attenuation in vivo, with reduced shedding and transmission to contact chickens. However, possession of BJ94-like H9N2 internal genes resulted in more rapid transmission and significantly elevated cloacal shedding compared to the parental Anhui/13 H7N9. In vitro analysis showed that the 2:6 H7N9 with BJ94-like internal genes had significantly increased replication compared to the Anhui/13 H7N9 in chicken cells. In vivo coinfection experiments followed, where chickens were coinfected with pairs of Anhui/13 H7N9 and a 2:6 H7N9 reassortant. During ensuing transmission events, the Anhui/13 H7N9 virus outcompeted 2:6 H7N9 AIVs with internal gene segments of BJ94-like or G1-like H9N2 viruses. Coinfection did lead to the emergence of novel reassortant genotypes that were transmitted to contact chickens. Some of the reassortant viruses had a greater replication in chicken and human cells compared to the progenitors. We demonstrated that the internal gene cassette determines the transmission fitness of H7N9 viruses in chickens, and the reassortment events can generate novel H7N9 genotypes with increased virulence in chickens and enhanced zoonotic potential. IMPORTANCE H9N2 avian influenza viruses (AIVs) are enzootic in poultry in different geographical regions. The internal genes of these viruses can be exchanged with other zoonotic AIVs, most notably the A/Anhui/1/2013-lineage H7N9, which can give rise to new virus genotypes with increased veterinary, economic and public health threats to both poultry and humans. We investigated the propensity of the internal genes of H9N2 viruses (G1 or BJ94) in the generation of novel reassortant H7N9 AIVs. We observed that the internal genes of H7N9 which were derivative of BJ94-like H9N2 virus have a fitness advantage compared to those from the G1-like H9N2 viruses for efficient transmission among chickens. We also observed the generation of novel reassortant viruses during chicken transmission which infected and replicated efficiently in human cells. Therefore, such emergent reassortant genotypes may pose an elevated zoonotic threat.

Reverse genetics based H5N2 vaccine provides clinical protection against H5N1, H5N8 and H9N2 avian influenza infection in chickens

The current study aimed to develop broadly protective vaccines for avian influenza. In an earlier study, HA stalk (universal flu vaccine) was found to be broadly protective against different subtypes of influenza virus in mice. Hence, we were interested to know its breadth of protective efficacy either alone or combined with inactivated rgH5N2 (clade 2.3.2.1a) vaccine against challenge viruses of homologous H5N1, heterologous H5N8 (clade 2.3.4.4) and heterosubtypic H9N2 virus in specific pathogen-free chickens. The rgH5N2 vaccine alone or in combination with HA stalk elicited sufficient pre-challenge immunity in the form of haemagglutination inhibiting (HI) antibodies and neutralizing antibodies (MNT) against H5N1, H5N8, and H9N2 in chickens. The rgH5N2 vaccine alone or in combination with HA stalk also attenuated the shedding of H5N1, H5N8 and H9N2 in chickens and protected against the lethal challenge of H5N1 or H5N8. In contrast, all HA stalk immunised chickens died upon H5N1 or H5N8 challenge and H9N2 challenged chickens survived. Our study suggests that the rgH5N2 vaccine can provide clinical protection against H5N1, H5N8 and can attenuate the viral shedding of H9N2 in chickens.

Coinfection of Chickens with H9N2 and H7N9 Avian Influenza Viruses Leads to Emergence of Reassortant H9N9 Virus with Increased Fitness for Poultry and a Zoonotic Potential

An H7N9 low-pathogenicity avian influenza virus (LPAIV) emerged in 2013 through genetic reassortment between H9N2 and other LPAIVs circulating in birds in China. This virus causes inapparent clinical disease in chickens, but zoonotic transmission results in severe and fatal disease in humans. To examine a natural reassortment scenario between H7N9 and G1 lineage H9N2 viruses predominant in the Indian subcontinent, we performed an experimental coinfection of chickens with A/Anhui/1/2013/H7N9 (Anhui/13) virus and A/Chicken/Pakistan/UDL-01/2008/H9N2 (UDL/08) virus. Plaque purification and genotyping of the reassortant viruses shed via the oropharynx of contact chickens showed H9N2 and H9N9 as predominant subtypes. The reassortant viruses shed by contact chickens also showed selective enrichment of polymerase genes from H9N2 virus. The viable "6+2" reassortant H9N9 (having nucleoprotein [NP] and neuraminidase [NA] from H7N9 and the remaining genes from H9N2) was successfully shed from the oropharynx of contact chickens, plus it showed an increased replication rate in human A549 cells and a significantly higher receptor binding to α2,6 and α2,3 sialoglycans compared to H9N2. The reassortant H9N9 virus also had a lower fusion pH, replicated in directly infected ferrets at similar levels compared to H7N9 and transmitted via direct contact. Ferrets exposed to H9N9 via aerosol contact were also found to be seropositive, compared to H7N9 aerosol contact ferrets. To the best of our knowledge, this is the first study demonstrating that cocirculation of H7N9 and G1 lineage H9N2 viruses could represent a threat for the generation of novel reassortant H9N9 viruses with greater virulence in poultry and a zoonotic potential. IMPORTANCE We evaluated the consequences of reassortment between the H7N9 and the contemporary H9N2 viruses of the G1 lineage that are enzootic in poultry across the Indian subcontinent and the Middle East. Coinfection of chickens with these viruses resulted in the emergence of novel reassortant H9N9 viruses with genes derived from both H9N2 and H7N9 viruses. The "6+2" reassortant H9N9 (having NP and NA from H7N9) virus was shed from contact chickens in a significantly higher proportion compared to most of the reassortant viruses, showed significantly increased replication fitness in human A549 cells, receptor binding toward human (α2,6) and avian (α2,3) sialic acid receptor analogues, and the potential to transmit via contact among ferrets. This study demonstrated the ability of viruses that already exist in nature to exchange genetic material, highlighting the potential emergence of viruses from these subtypes with zoonotic potential.

A ligation and restriction enzyme independent cloning technique: an alternative to conventional methods for cloning hard-to-clone gene segments in the influenza reverse genetics system

BACKGROUND

Reverse genetics is used in many laboratories around the world and enables the creation of tailor-made influenza viruses with a desired genotype or phenotype. However, the process is not flawless, and difficulties remain during cloning of influenza gene segments into reverse genetics vectors (pHW2000, pHH21, pCAGGS). Reverse genetics begins with making cDNA copies of influenza gene segments and cloning them into bi-directional (pHW2000) or uni-directional plasmids (pHH21, pCAGGS) followed by transfection of the recombinant plasmid(s) to HEK-293 T or any other suitable cells which are permissive to transfection. However, the presence of internal restriction sites in the gene segments of many field isolates of avian influenza viruses makes the cloning process difficult, if employing conventional methods. Further, the genetic instability of influenza gene-containing plasmids in bacteria (especially Polymerase Basic 2 and Polymerase Basic 1 genes; PB2 and PB1) also leads to erroneous incorporation of bacterial genomic sequences into the influenza gene of interest.

METHODS

Herein, we report an easy and efficient ligation and restriction enzyme independent (LREI) cloning method for cloning influenza gene segments into pHW2000 vector. The method involves amplification of megaprimers followed by PCR amplification of megaprimers using a bait plasmid, DpnI digestion and transformation.

RESULTS

Hard-to-clone genes: PB2 of A/chicken/Bangladesh/23527/2014 (H9N2) and PB1 of A/chicken/Bangladesh/23527/2014 (H9N2), A/chicken/Jiangxi/02.05YGYXG023-P/2015 (H5N6) and A/Chicken/Vietnam/H7F-14-BN4-315/2014 (H9N2) were cloned into pHW2000 using our LREI method and recombinant viruses were subsequently rescued.

CONCLUSION

The LREI cloning procedure represents an alternative strategy for cloning influenza gene segments which have internal restriction sites for the enzymes used in reverse genetics. Further, the problem of genetic instability in bacteria can be alleviated by growing recombinant bacterial cultures at a lower temperature. This technique can be applied to clone any influenza gene segment using universal primers, which would help in rapid generation of influenza viruses and facilitate influenza research and vaccine development.