Rapid virulence shift of an H5N2 avian influenza virus during a single passage in mice

Genetic Characterization and Pathogenesis of Three Novel Reassortant H5N2 Viruses in South Korea, 2018

The outbreaks of H5N2 avian influenza viruses have occasionally caused the death of thousands of birds in poultry farms. Surveillance during the 2018 winter season in South Korea revealed three H5N2 isolates in feces samples collected from wild birds (KNU18-28: A/Wild duck/South Korea/KNU18-28/2018, KNU18-86: A/Bean Goose/South Korea/KNU18-86/2018, and KNU18-93: A/Wild duck/South Korea/KNU18-93/2018). Phylogenetic tree analysis revealed that these viruses arose from reassortment events among various virus subtypes circulating in South Korea and other countries in the East Asia–Australasian Flyway. The NS gene of the KNU18-28 and KNU18-86 isolates was closely related to that of China’s H10N3 strain, whereas the KNU18-93 strain originated from the H12N2 strain in Japan, showing two different reassortment events and different from a low pathogenic H5N3 (KNU18-91) virus which was isolated at the same day and same place with KNU18-86 and KNU18-93. These H5N2 isolates were characterized as low pathogenic avian influenza viruses. However, many amino acid changes in eight gene segments were identified to enhance polymerase activity and increase adaptation and virulence in mice and mammals. Experiments reveal that viral replication in MDCK cells was quite high after 12 hpi, showing the ability to replicate in mouse lungs. The hematoxylin and eosin-stained (H&E) lung sections indicated different degrees of pathogenicity of the three H5N2 isolates in mice compared with that of the control H1N1 strain. The continuing circulation of these H5N2 viruses may represent a potential threat to mammals and humans. Our findings highlight the need for intensive surveillance of avian influenza virus circulation in South Korea to prevent the risks posed by these reassortment viruses to animal and public health.

Genetic analysis and biological characteristics of novel clade 2.3.4.4 reassortment H5N6 avian influenza viruses from poultry in eastern China in 2016

OBJECTIVES

The continuous evolution of highly pathogenic H5N6 avian influenza viruses (AIVs) causes outbreaks in wildfowl and poultry, and occasional human infections. The aim of this study was to better understand the genetic relationships between these H5N6 AIVs from eastern China and other AIVs.

METHODS

In 2016, 1623 cloacal swabs were sampled from poultry in 18 LPMs in eastern China, and subsequently characterized systematically using gene sequencing, phylogenetic studies, and antigenic analysis. In addition, their pathogenicity in mammals was studied in BALB/c mice, which were inoculated with viruses, with survival rate and body weight recorded daily for 14 days.

RESULTS

In total, 56 H5N6 AIVs were isolated in eastern China and five representative isolates were selected for further study. In our study, the H5N6 AIVs clustered into clade 2.3.4.4, Group C, and their six internal segments were derived from H6N6 and H9N2 viruses, or both, suggesting extensive reassortant among H5N6 AIVs with other subtypes. These H5N6 viruses could replicate in the lungs without prior adaptation, and exhibited slight-to-moderate virulence in mice.

CONCLUSIONS

The continuous circulation of these novel H5N6 viruses suggests the importance of persistent surveillance of H5N6 AIVs in poultry.

Less severe clinical symptoms of Norwalk virus 8fIIb inoculum compared to its precursor 8fIIa from human challenge studies

Noroviruses (NoV) are a leading cause of epidemic gastroenteritis. Human challenge studies have been used to examine the infectivity, pathogenicity, and host immune response to NoV as well as vaccine efficacy. The goal of this study was to conduct a meta-analysis of data from five previously completed human challenge trials and compare the response to the secondary NV inoculum (8fIIb) to its precursor (8fIIa). We investigated a total of 158 subjects: 76 subjects were experimentally challenged with NV inoculum 8fIIa, and 82 subjects were challenged with 8fIIb. We compared demographic characteristics, infection, illness, mean severity score, blood types, and duration of viral shedding between the two groups of subjects. There were no statistically significant differences in overall infection and illness rates between subjects inoculated with 8fIIa and 8fIIb. However, individuals challenged with 8fIIa had significantly higher severity scores (5.05 vs. 3.22, p = .008) compared with those challenged with 8fIIb. We also observed that infection with 8fIIb was associated with significantly longer duration of viral shedding compared with 8fIIa (11.0 days vs. 5.0 days, p = .0005). These results have serious implications for the development of new NoV inocula for human challenge studies to test candidate vaccine efficacy-where illness severity and duration of viral shedding are important outcomes.

Inhibitory effects of aprotinin on influenza A and B viruses in vitro and in vivo

Influenza viruses cause significant morbidity and mortality worldwide. Long-term or frequent use of approved anti-influenza agents has resulted in drug-resistant strains, thereby necessitating the discovery of new drugs. In this study, we found aprotinin, a serine protease inhibitor, as an anti-influenza candidate through screening of compound libraries. Aprotinin has been previously reported to show inhibitory effects on a few influenza A virus (IAV) subtypes (e.g., seasonal H1N1 and H3N2). However, because there were no reports of its inhibitory effects on the other types of influenza viruses, we investigated the inhibitory effects of aprotinin in vitro on a wide range of influenza viruses, including avian and oseltamivir-resistant influenza virus strains. Our cell-based assay showed that aprotinin had inhibitory effects on seasonal human IAVs (H1N1 and H3N2 subtypes), avian IAVs (H5N2, H6N5, and H9N2 subtypes), an oseltamivir-resistant IAV, and a currently circulating influenza B virus. We have also confirmed its activity in mice infected with a lethal dose of influenza virus, showing a significant increase in survival rate. Our findings suggest that aprotinin has the capacity to inhibit a wide range of influenza virus subtypes and should be considered for development as a therapeutic agent against influenza.

Multiple amino acid substitutions involved in the adaption of three avian-origin H7N9 influenza viruses in mice

Background

Avian influenza A H7N9 virus has caused five outbreak waves of human infections in China since 2013 and posed a dual challenge to public health and poultry industry. The number of reported H7N9 virus human cases confirmed by laboratory has surpassed that of H5N1 virus. However, the mechanism for how H7N9 influenza virus overcomes host range barrier has not been clearly understood.

Methods

To generate mouse-adapted H7N9 influenza viruses, we passaged three avian-origin H7N9 viruses in mice by lung-to-lung passages independently. Then, the characteristics between the parental and mouse-adapted H7N9 viruses was compared in the following aspects, including virulence in mice, tropism of different tissues, replication in MDCK cells and molecular mutations.

Results

After ten passages in mice, MLD₅₀ of the H7N9 viruses reduced >750-3,160,000 folds, and virus titers in MDCK cells increased 10-200 folds at 48 hours post-inoculation. Moreover, the mouse-adapted H7N9 viruses showed more expanded tissue tropism and more serious lung pathological lesions in mice. Further analysis of the amino acids changes revealed 10 amino acid substitutions located in PB2 (E627K), PB1 (W215R and D638G), PA (T97I), HA (H3 numbering: R220G, L226S, G279R and G493R) and NA (P3Q and R134I) proteins. Moreover, PB2 E627K substitution was shared by the three mouse-adapted viruses (two viruses belong to YRD lineage and one virus belongs to PRD lineage), and PA T97A substitution was shared by two mouse-adapted viruses (belong to YRD lineage).

Conclusions

Our result indicated that the virulence in mice and virus titer in MDCK cells of H7N9 viruses significantly increased after adapted in mouse model. PB2 E627K and PA T97A substitutions are vital in mouse adaption and should be monitored during epidemiological study of H7N9 virus.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-1109-1) contains supplementary material, which is available to authorized users.

Adaptive Evolution of Human-Isolated H5Nx Avian Influenza A Viruses

Avian influenza A viruses (AIVs) H5N1, first identified in 1996, are highly pathogenic in domestic poultry and continue to occasionally infect humans. In this study, we sought to identify genetic changes that occurred during their multiple invasions to humans. We evaluated all available H5Nx AIV genomes. Significant signals of positive selection were detected in 29 host-shift branches. 126 parallel evolution sites were detected on these branches, including 17 well-known sites (such as T271A, A274T, T339M, Q591K, E627K, and D701N in PB2; A134V, D154N, S223N, and R497K in HA) that play roles in allowing AIVs to cross species barriers. Our study suggests that during human infections, H5Nx viruses have experienced adaptive evolution (positive selection and convergent evolution) that allowed them to adapt to their new host environments. Analyses of adaptive evolution should be useful in identifying candidate sites that play roles in human infections, which can be tested by functional experiments.

Virological and pathological characterization of an avian H1N1 influenza A virus

Gene segments from avian H1N1 influenza A viruses have reassorted with other influenza viruses to generate pandemic strains over the past century. Nevertheless, little effort has been invested in understanding the characteristics of avian H1N1 influenza viruses. Here, we present the genome sequence and a molecular and virological characterization of an avian influenza A virus, A/wild bird/Korea/SK14/2014 (A/SK14, H1N1), isolated from migratory birds in South Korea during the winter season of 2014-2015. Full-genome sequencing and phylogenetic analysis revealed that the virus belongs to the Eurasian avian lineage. Although it retained avian-receptor binding preference, A/SK14 virus also exhibited detectable human-like receptor binding and was able to replicate in differentiated primary normal human bronchial epithelial cells. In animal models, A/SK14 virus was moderately pathogenic in mice, and virus was detected in nasal washes from inoculated guinea pigs, but not in direct-contact guinea pigs. Although A/SK14 showed moderate pathogenicity and no evidence of transmission in a mammalian model, our results suggest that the dual receptor specificity of A/SK14-like virus might allow for a more rapid adaptation to mammals, emphasizing the importance of further continuous surveillance and risk-assessment activities.