Avian influenza A H5N1 virus

Responding to avian influenza A H5N1 detection on a hospital property in Maine-An interdisciplinary approach

BACKGROUND

The risk of infection with avian influenza A viruses currently circulating in wild and domestic birds in the Americas is considered low for the general public; however, detections in humans have been reported and warning signs of increased zoonotic potential have been identified. In December 2022, two Canada geese residing on the grounds of an urban hospital in Maine tested positive for influenza A H5N1 clade 2.3.4.4b.

AIMS

Given the opportunity for exposure to staff and hospital visitors through potentially infected faeces on the property, public health authorities determined mitigation efforts were needed to prevent the spread of disease. The ensuing response relied on collaboration between the public health and animal health agencies to guide the hospital through efforts in preventing possible zoonotic transmission to humans.

MATERIALS AND METHODS

Mitigation efforts included staff communication and education, environmental cleaning and disinfection, enhanced illness surveillance among staff and patients, and exposure and source reduction.

RESULTS

No human H5N1 cases were identified, and no additional detections in birds on the property occurred. Hospital staff identified barriers to preparedness resulting from a lack of understanding of avian influenza A viruses and transmission prevention methods, including avian influenza risk in resident wild bird populations and proper wildlife management methods.

CONCLUSION

As this virus continues to circulate at the animal-human interface, this event and resulting response highlights the need for influenza A H5N1 risk awareness and guidance for facilities and groups not traditionally involved in avian influenza responses.

Construction of a recombinant duck enteritis virus (DEV) expressing hemagglutinin of H5N1 avian influenza virus based on an infectious clone of DEV vaccine strain and evaluation of its efficacy in ducks and chickens

Background

Highly pathogenic avian influenza virus (AIV) subtype H5N1 remains a threat to poultry. Duck enteritis virus (DEV)-vectored vaccines expressing AIV H5N1 hemagglutinin (HA) may be viable AIV and DEV vaccine candidates.

Methods

To facilitate the generation and further improvement of DEV-vectored HA(H5) vaccines, we first constructed an infectious clone of DEV Chinese vaccine strain C-KCE (DEV^C-KCE). Then, we generated a DEV-vectored HA(H5) vaccine (DEV-H5(UL55)) based on the bacterial artificial chromosome (BAC) by inserting a synthesized HA(H5) expression cassette with a pMCMV IE promoter and a consensus HA sequence into the noncoding area between UL55 and LORF11. The immunogenicity and protective efficacy of the resulting recombinant vaccine against DEV and AIV H5N1 were evaluated in both ducks and chickens.

Results

The successful construction of DEV BAC and DEV-H5(UL55) was verified by restriction fragment length polymorphism analysis. Recovered virus from the BAC or mutants showed similar growth kinetics to their parental viruses. The robust expression of HA in chicken embryo fibroblasts infected with the DEV-vectored vaccine was confirmed by indirect immunofluorescence and western blotting analyses. A single dose of 10⁶ TCID₅₀ DEV-vectored vaccine provided 100 % protection against duck viral enteritis in ducks, and the hemagglutination inhibition (HI) antibody titer of AIV H5N1 with a peak of 8.2 log₂ was detected in 3-week-old layer chickens. In contrast, only very weak HI titers were observed in ducks immunized with 10⁷ TCID₅₀ DEV-vectored vaccine. A mortality rate of 60 % (6/10) was observed in 1-week-old specific pathogen free chickens inoculated with 10⁶ TCID₅₀ DEV-vectored vaccine.

Conclusions

We demonstrate the following in this study. (i) The constructed BAC is a whole genome clone of DEV^C-KCE. (ii) The insertion of an HA expression cassette sequence into the noncoding area between UL55 and LORF11 of DEV^C-KCE affects neither the growth kinetics of the virus nor its protection against DEV. (iii) DEV-H5(UL55) can generate a strong humoral immune response in 3-week-old chickens, despite the virulence of this virus observed in 1-week-old chickens. (iv) DEV-H5(UL55) induces a weak HI titer in ducks. An increase in the HI titers induced by DEV-vectored HA(H5) will be required prior to its wide application.

Differential host response, rather than early viral replication efficiency, correlates with pathogenicity caused by influenza viruses

Influenza viruses exhibit large, strain-dependent differences in pathogenicity in mammalian hosts. Although the characteristics of severe disease, including uncontrolled viral replication, infection of the lower airway, and highly inflammatory cytokine responses have been extensively documented, the specific virulence mechanisms that distinguish highly pathogenic strains remain elusive. In this study, we focused on the early events in influenza infection, measuring the growth rate of three strains of varying pathogenicity in the mouse airway epithelium and simultaneously examining the global host transcriptional response over the first 24 hours. Although all strains replicated equally rapidly over the first viral life-cycle, their growth rates in both lung and tracheal tissue strongly diverged at later times, resulting in nearly 10-fold differences in viral load by 24 hours following infection. We identified separate networks of genes in both the lung and tracheal tissues whose rapid up-regulation at early time points by specific strains correlated with a reduced viral replication rate of those strains. The set of early-induced genes in the lung that led to viral growth restriction is enriched for both NF-κB binding site motifs and members of the TREM1 and IL-17 signaling pathways, suggesting that rapid, NF-κB –mediated activation of these pathways may contribute to control of viral replication. Because influenza infection extending into the lung generally results in severe disease, early activation of these pathways may be one factor distinguishing high- and low-pathogenicity strains.

An overview of the highly pathogenic H5N1 influenza virus

Since the first human case of H5N1 avian influenza virus infection was reported in 1997, this highly pathogenic virus has infected hundreds of people around the world and resulted in many deaths. The ability of H5N1 to cross species boundaries, and the presence of polymorphisms that enhance virulence, present challenges to developing clear strategies to prevent the pandemic spread of this highly pathogenic avian influenza (HPAI) virus. This review summarizes the current understanding of, and recent research on, the avian influenza H5N1 virus, including transmission, virulence, pathogenesis, clinical characteristics, treatment and prevention.

Effects of route and coadministration of recombinant raccoon poxviruses on immune responses and protection against highly pathogenic avian influenza in mice

We previously demonstrated that recombinant raccoonpox (RCN) virus could serve as a vector for an influenza vaccine. RCN constructs expressing the hemagglutinin (HA) from H5N1 viruses were immunogenic in chickens. In the current study, we generated several recombinant RCN constructs expressing influenza (H5N1) antigens and a molecular adjuvant (Heat-Labile enterotoxin B from E. coli: RCN-LTB), demonstrated their expression in vitro, and evaluated their ability to protect mice against H5N1 virus challenge. RCN-HA provided strong protection when administered intradermally (ID), but not intranasally (IN). Conversely, the RCN-neuraminidase (NA) construct was highly efficacious by the IN route and elicited high titers of neutralizing antibodies in mice. Vaccination by combined ID (RCN-HA) and IN (RCN-NA) routes offered mice the best protection against an IN challenge with heterologous H5N1 virus. However, protection was reduced when the different RCN constructs were pre-mixed, perhaps due to reduced expression of antigen.

Treatment options for H5N1: lessons learned from the H1N1 pandemic

Human infections with avian influenza A (H5N1) are relatively rare but are associated with high mortality. As of July 5, 2010 there had been 500 cases and 296 fatalities. The influenza virus readily undergoes mutation and reassortment, and there are concerns that an H5N1 variant could be responsible for a future pandemic. The influenza neuraminidase inhibitors zanamivir and oseltamivir are approved for the treatment and prophylaxis of influenza. Oseltamivir is being used to treat H5N1 infections and the case has been made for a role for zanamivir; however, there are no case reports for the latter. Zanamivir is a potent inhibitor of H5N1, attains high lung concentrations immediately on administration, distributes into plasma at antiviral concentrations, has a low propensity for generating resistant virus, and retains activity against H275Y oseltamivir-resistant virus. There have been several reports of oseltamivir-resistant H5N1 arising during treatment with oseltamivir, and zanamivir retains effectiveness (in vitro or in vivo) against these isolates. Compassionate use of intravenous zanamivir for the treatment of seriously ill patients, including those with H275Y H1N1 infections, has also shown promising results. It is concluded that there is a role for zanamivir in treating H5N1 infections either as the approved, inhaled formulation in patients capable of using the Diskhaler, or as the intravenous formulation if compassionate use is warranted. The relatively small number of patients with these infections remains an obstacle to completion of clinical trials. Evidence is therefore likely to be based on carefully documented case reports, ideally in patients treated early in the course of the infection.