Inactivation of avian influenza viruses by hydrostatic pressure as a potential vaccine development approach

Vaccines are a recommended strategy for controlling influenza A infections in humans and animals. Here, we describe the effects of hydrostatic pressure on the structure, morphology and functional characteristics of avian influenza A H3N8 virus. The effect of hydrostatic pressure for 3 h on H3N8 virus revealed that the particles were resistant to this condition, and the virus displayed only a discrete conformational change. We found that pressure of 3 kbar applied for 6 h was able to inhibit haemagglutination and infectivity while virus replication was no longer observed, suggesting that full virus inactivation occurred at this point. However, the neuraminidase activity was not affected at this approach suggesting the maintenance of neutralizing antibody epitopes in this key antigen. Our data bring important information for the area of structural virology of enveloped particles and support the idea of applying pressure-induced inactivation as a tool for vaccine production.

Complete Coding Genome Sequence of an Avian Influenza A/H3N8 Virus Strain Detected in North Kazakhstan in 2018

ABSTRACT We report the complete coding genome sequence of the influenza A/H3N8 virus, isolated from Anas querquedula in northern Kazakhstan in 2018. Phylogenetic analysis of the surface antigens of strain A/garganey/North-Kazakhstan/45/2018 showed that its hemagglutinin belonged to the Asian line, while its neuraminidase was assigned to the Eurasian group.

Novel Reassortant Avian Influenza A(H3N8) Virus Isolated from a Wild Bird in Jiangxi, China

Here, we report the detection of a reassortant avian influenza A(H3N8) virus isolated from a wild bird in Poyang Lake, Jiangxi, China, in 2014. Phylogenetic analyses indicated that this virus is most likely derived from the Eurasian-origin H3Ny and HxN8 viruses and two strains endemic to China, namely, H5N1 and H5N6.

Mutation W222L at the Receptor Binding Site of Hemagglutinin Could Facilitate Viral Adaption from Equine Influenza A(H3N8) Virus to Dogs

ABSTRACT An outbreak of respiratory disease caused by the equine-origin influenza A(H3N8) virus was first detected in dogs in 2004 and since then has been enzootic among dogs. Currently, the molecular mechanisms underlying host adaption of this virus from horses to dogs is unknown. Here, we have applied quantitative binding, growth kinetics, and immunofluorescence analyses to elucidate these mechanisms. Our findings suggest that a substitution of W222L in the hemagglutinin of the equine-origin A(H3N8) virus facilitated its host adaption to dogs. This mutation increased binding avidity of the virus specifically to receptor glycans with N-glycolylneuraminic acid (Neu5Gc) and sialyl Lewis X (SLeX) motifs. We have demonstrated these motifs are abundantly located in the submucosal glands of dog trachea. Our findings also suggest that in addition to the type of glycosidic linkage (e.g., α2,3-linkage or α2,6-linkage), the type of sialic acid (Neu5Gc or 5-N-acetyl neuraminic acid) and the glycan substructure (e.g., SLeX) also play an important role in host tropism of influenza A viruses. IMPORTANCE Influenza A viruses (IAVs) cause a significant burden on human and animal health, and mechanisms for interspecies transmission of IAVs are far from being understood. Findings from this study suggest that an equine-origin A(H3N8) IAV with mutation W222L at its hemagglutinin increased binding to canine-specific receptors with sialyl Lewis X and Neu5Gc motifs and, thereby, may have facilitated viral adaption from horses to dogs. These findings suggest that in addition to the glycosidic linkage (e.g., α2,3-linked and α2,6-linked), the substructure in the receptor saccharides (e.g., sialyl Lewis X and Neu5Gc) could present an interspecies transmission barrier for IAVs and drive viral mutations to overcome such barriers.

Complete Genome Sequencing of Two Equine Influenza A(H3N8) Virus Strains Isolated in Kazakhstan

Here, we report the complete genome sequencing of strains A/equine/Kostanay/9/2012(H3N8) and A/equine/LKZ/9/2012(H3N8) of the equine influenza virus belonging to Florida sublineage, clade 2. The strains were isolated in 2012 in the northern and southern regions of Kazakhstan, respectively.

Competition between IAV subtypes through heterosubtypic immunity modulates re-infection and antibody dynamics in the mallard reservoir

Our overall hypothesis is that host population immunity directed at multiple antigens will influence the prevalence, diversity and evolution of influenza A virus (IAV) in avian populations where the vast subtype diversity is maintained. To investigate how initial infection influences the outcome of later infections with homologous or heterologous IAV subtypes and how viruses interact through host immune responses; we carried out experimental infections in mallard ducks (Anas platyrhynchos). Mallards were pre-challenged with an H3N8 low-pathogenic IAV and were divided into six groups. At five weeks post H3N8 inoculation, each group was challenged with a different IAV subtype or the same H3N8. Two additional pre-challenged groups were inoculated with the homologous H3N8 virus at weeks 11 and 15 after pre-challenge to evaluate the duration of protection, which showed that mallards were still resistant to re-infection after 15 weeks. There was a significant reduction in shedding for all pre-challenged groups compared to controls and the outcome of the heterologous challenges varied according to hemagglutinin (HA) phylogenetic relatedness between the viruses used. There was a boost in the H3 antibody titer after re-infection with H4N5, which is consistent with original antigenic sin or antigenic seniority and suggest a putative strategy of virus evasion. These results imply strong competition between related subtypes that could regulate IAV subtype population dynamics in nature. Collectively, we provide new insights into within-host IAV complex interactions as drivers of IAV antigenic diversity that could allow the circulation of multiple subtypes in wild ducks.Author summaryMany features of pathogen diversification remain poorly explored although host immunity is recognized as a major driver of pathogen evolution. Influenza A viruses (IAVs) can infect many avian and mammalian hosts, but while few IAV subtypes circulate in human populations, subtype diversity is extensive in wild bird populations. How do these subtypes coexist in wild avian populations and do they compete within these natural host populations? Here we experimentally challenged mallard ducks with different IAVs to study how an initial infection with H3N8 determines the outcome of later infections (duration of infection and virus load) and antibody responses. There was complete protection to re-infection with the same H3N8 virus based on virus isolation. In addition, there was partial protection induced by H3N8 pre-challenge to other subtypes and development of heterosubtypic immunity indicated by shorter infections and reduction in viral load compared to controls. This indicates that subtype dynamics in the host population are not independent. Amongst H3N8 pre-challenged groups, the highest protection was conferred to the H4N5 subtype which was most genetically related to H3N8. The H4N5 challenge also induced an increase in H3 antibody levels and evidence for antigenic seniority. Thus, previous infections with IAV can influence the outcome of subsequent infection with different IAV subtypes. Results not only have relevance to understanding naturally occurring subtype diversity in wild avian populations but also in understanding potential outcomes associated with introduction of novel viruses such as highly pathogenic IAV H5 viruses in wild bird populations.Author contributionsConceived and designed the experiments: NLM, DES. Performed the experiments: NLM, JDB, AF, DC, MF, DES. Contributed reagents/materials/analysis tools: NLM, JB, AF, RLP, DES. Analyzed the data: NLM, DES. Wrote the paper: NLM, JDB, AF, RLP, DC, MF, DES