Multiyear Serological Surveillance of Notifiable Influenza A Viruses in Belgian Poultry: A Retrospective Analysis

Long-Term Protective Effect of Serial Infections with H5N8 Highly Pathogenic Avian Influenza Virus in Wild Ducks

Highly pathogenic avian influenza viruses (HPAIVs) of the Goose/Guangdong (Gs/Gd) lineage are an emerging threat to wild birds. In the 2016-2017 H5N8 outbreak, unexplained variability was observed in susceptible species, with some reports of infected birds dying in high numbers and other reports of apparently subclinical infections. This experimental study was devised to test the hypothesis that previous infection with a less-virulent HPAIV (i.e., 2014 H5N8) provides long-term immunity against subsequent infection with a more-virulent HPAIV (i.e., 2016 H5N8). Therefore, two species of wild ducks-the more-susceptible tufted duck (Aythya fuligula) and the more-resistant mallard (Anas platyrhynchos)-were serially inoculated, first with 2014 H5N8 and after 9 months with 2016 H5N8. For both species, a control group of birds was first sham inoculated and after 9 months inoculated with 2016 H5N8. Subsequent infection with the more-virulent 2016 H5N8 caused no clinical signs in tufted ducks that had previously been infected with 2014 H5N8 (n = 6) but caused one death in tufted ducks that had been sham inoculated (n = 7). In mallards, 2016 H5N8 infection caused significant body weight loss in previously sham-inoculated birds (n = 8) but not in previously infected birds (n = 7). IMPORTANCE This study showed that ducks infected with a less-virulent HPAIV developed immunity that was protective against a subsequent infection with a more-virulent HPAIV 9 months later. Following 2014 H5N8 infection, the proportion of birds with detectable influenza nucleoprotein antibody declined from 100% (8/8) in tufted ducks and 78% (7/9) in mallards after 1 month to 33% (2/6) in tufted ducks and 29% (2/7) in mallards after 9 months. This finding helps predict the expected impact that an HPAIV outbreak may have on wild bird populations, depending on whether they are immunologically naive or have survived previous infection with HPAIV.

Broadly Reactive H2 Hemagglutinin Vaccines Elicit Cross-Reactive Antibodies in Ferrets Preimmune to Seasonal Influenza A Viruses

Influenza vaccines have traditionally been tested in naive mice and ferrets. However, humans are first exposed to influenza viruses within the first few years of their lives. Therefore, there is a pressing need to test influenza virus vaccines in animal models that have been previously exposed to influenza viruses before being vaccinated. In this study, previously described H2 computationally optimized broadly reactive antigen (COBRA) hemagglutinin (HA) vaccines (Z1 and Z5) were tested in influenza virus “preimmune” ferret models. Ferrets were infected with historical, seasonal influenza viruses to establish preimmunity. These preimmune ferrets were then vaccinated with either COBRA H2 HA recombinant proteins or wild-type H2 HA recombinant proteins in a prime-boost regimen. A set of naive preimmune or nonpreimmune ferrets were also vaccinated to control for the effects of the multiple different preimmunities. All of the ferrets were then challenged with a swine H2N3 influenza virus. Ferrets with preexisting immune responses influenced recombinant H2 HA-elicited antibodies following vaccination, as measured by hemagglutination inhibition (HAI) and classical neutralization assays. Having both H3N2 and H1N1 immunological memory regardless of the order of exposure significantly decreased viral nasal wash titers and completely protected all ferrets from both morbidity and mortality, including the mock-vaccinated ferrets in the group. While the vast majority of the preimmune ferrets were protected from both morbidity and mortality across all of the different preimmunities, the Z1 COBRA HA-vaccinated ferrets had significantly higher antibody titers and recognized the highest number of H2 influenza viruses in a classical neutralization assay compared to the other H2 HA vaccines.

IMPORTANCE H1N1 and H3N2 influenza viruses have cocirculated in the human population since 1977. Nearly every human alive today has antibodies and memory B and T cells against these two subtypes of influenza viruses. H2N2 influenza viruses caused the 1957 global pandemic and people born after 1968 have never been exposed to H2 influenza viruses. It is quite likely that a future H2 influenza virus could transmit within the human population and start a new global pandemic, since the majority of people alive today are immunologically naive to viruses of this subtype. Therefore, an effective vaccine for H2 influenza viruses should be tested in an animal model with previous exposure to influenza viruses that have circulated in humans. Ferrets were infected with historical influenza A viruses to more accurately mimic the immune responses in people who have preexisting immune responses to seasonal influenza viruses. In this study, preimmune ferrets were vaccinated with wild-type (WT) and COBRA H2 recombinant HA proteins in order to examine the effects that preexisting immunity to seasonal human influenza viruses have on the elicitation of broadly cross-reactive antibodies from heterologous vaccination.

Computationally Optimized Broadly Reactive H2 HA Influenza Vaccines Elicited Broadly Cross-Reactive Antibodies and Protected Mice from Viral Challenges

Influenza viruses have caused numerous pandemics throughout human history. The 1957 influenza pandemic was initiated by an H2N2 influenza virus. This H2N2 influenza virus was the result of a reassortment event between a circulating H2N2 avian virus and the seasonal H1N1 viruses in humans. Previously, our group has demonstrated the effectiveness of hemagglutinin (HA) antigens derived using computationally optimized broadly reactive antigen (COBRA) methodology against H1N1, H3N2, and H5N1 viruses. Using the COBRA methodology, H2 HA COBRA antigens were designed using sequences from H2N2 viruses isolated from humans in the 1950s and 1960s, as well as H2Nx viruses isolated from avian and mammalian species between the 1950s and 2016. In this study, the effectiveness of H2 COBRA HA antigens (Z1, Z3, Z5, and Z7) was evaluated in DBA/2J mice and compared to that of wild-type H2 HA antigens. The COBRA HA vaccines elicited neutralizing antibodies to the majority of viruses in our H2 HA panel and across all three clades as measured by hemagglutination inhibition (HAI) and neutralization assays. Comparatively, several wild-type HA vaccines elicited antibodies against a majority of the viruses in the H2 HA panel. DBA/2J mice vaccinated with COBRA vaccines showed increase survival for all three viral challenges compared to the wild-type H2 vaccines. In particular, the Z1 COBRA is a promising candidate for future work toward a pandemic H2 influenza vaccine.IMPORTANCE H2N2 influenza has caused at least one pandemic in the past. Given that individuals born after 1968 have not been exposed to H2N2 influenza viruses, a future pandemic caused by H2 influenza is likely. An effective H2 influenza vaccine would need to elicit broadly cross-reactive antibodies to multiple H2 influenza viruses. Choosing a wild-type virus to create a vaccine may elicit a narrow immune response and not protect against multiple H2 influenza viruses. COBRA H2 HA vaccines were developed and evaluated in mice along with wild-type H2 HA vaccines. Multiple COBRA H2 HA vaccines protected mice from all three viral challenges and produced broadly cross-reactive neutralizing antibodies to H2 influenza viruses.

Ducks Are Susceptible to Infection with a Range of Doses of H5N8 Highly Pathogenic Avian Influenza Virus (2016, Clade 2.3.4.4b) and Are Largely Resistant to Virus-Specific Mortality, but Efficiently Transmit Infection to Contact Turkeys

Widespread H5N8 highly pathogenic avian influenza virus (HPAIV; clade 2.3.4.4b) infections occurred in wild birds and poultry across Europe during winter 2016-17. Four different doses of H5N8 HPAIV (A/wigeon/Wales/052833/2016 [wg-Wal-16]) were used to infect 23 Pekin ducks divided into four separate pens, with three contact turkeys introduced for cohousing per pen at 1 day postinfection (dpi). All doses resulted in successful duck infection, with four sporadic mortalities recorded among the 23 (17%) infected ducks, which appeared unrelated to the dose. The ducks transmitted wg-Wal-16 efficiently to the contact turkeys; all 12 (100%) turkeys died. Systemic viral dissemination was detected in multiple organs in two duck mortalities, with limited viral dissemination in another duck, which died after resolution of shedding. Systemic viral tropism was observed in two of the turkeys. The study demonstrated the utility of Pekin ducks as surrogates of infected waterfowl to model the wild bird/gallinaceous poultry interface for introduction of H5N8 HPAIV into terrestrial poultry, where contact turkeys served as a susceptible host. Detection of H5N8-specific antibody up to 58 dpi assured the value of serologic surveillance in farmed ducks by hemagglutination inhibition and anti-nucleoprotein ELISAs.

H2 influenza viruses: designing vaccines against future H2 pandemics

Influenza-related pathologies affect millions of people each year and the impact of influenza on the global economy and in our everyday lives has been well documented. Influenza viruses not only infect humans but also are zoonotic pathogens that infect various avian and mammalian species, which serve as viral reservoirs. While there are several strains of influenza currently circulating in animal species, H2 influenza viruses have a unique history and are of particular concern. The 1957 'Asian Flu' pandemic was caused by H2N2 influenza viruses and circulated among humans from 1957 to 1968 before it was replaced by viruses of the H3N2 subtype. This review focuses on avian influenza viruses of the H2 subtype and the role these viruses play in human infections. H2 influenza viral infections in humans would present a unique challenge to medical and scientific researchers. Much of the world's population lacks any pre-existing immunity to the H2N2 viruses that circulated 50-60 years ago. If viruses of this subtype began circulating in the human population again, the majority of people alive today would have no immunity to H2 influenza viruses. Since H2N2 influenza viruses have effectively circulated in people in the past, there is a need for additional research to characterize currently circulating H2 influenza viruses. There is also a need to stockpile vaccines that are effective against both historical H2 laboratory isolates and H2 viruses currently circulating in birds to protect against a future pandemic.