Interspecies transmission of influenza viruses: H5N1 virus and a Hong Kong SAR perspective

Vaccination of Poultry Against Influenza

The complexity of influenza A virus (IAV) infections in avian hosts leads to equally complex scenarios for the vaccination of poultry. Vaccination against avian influenza strains can be used to prevent infections from sources with a single strain of IAV. It has been used as a part of outbreak control strategies as well as a way to maintain production for both low and high pathogenicity outbreaks. Unlike other viral pathogens of birds, avian influenza vaccination when used against highly pathogenic avian influenza virus, is tied to international trade and thus is not freely available for use without specific permission.

Bacterial and viral rodent-borne infections on poultry farms. An attempt at a systematic review

Introduction

Rodents are quite common at livestock production sites. Their adaptability, high reproductive capacity and omnivorousness make them apt to become a source of disease transmission to humans and animals. Rodents can serve as mechanical vectors or active shedders of many bacteria and viruses, and their transmission can occur through direct contact, or indirectly through contaminated food and water or by the arthropods which parasitise infected rodents. This review paper summarises how rodents spread infectious diseases in poultry production.

Material and Methods

The aim of this review was to use PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) principles to meta-analyse the available data on this topic. Three databases – PubMed, Web of Science and Scopus – and grey literature were searched for papers published from inception to July 2022 using the established keywords.

Results

An initial search identified 2,999 articles that met the criteria established by the keywords. This number remained after removing 597 articles that were repeated in some databases. The articles were searched for any mention of specific bacterial and viral pathogens.

Conclusion

The importance of rodents in the spread of bacterial diseases in poultry has been established, and the vast majority of such diseases involved Salmonella, Campylobacter, Escherichia coli, Staphylococcus (MRSA), Pasteurella, Erysipelothrix or Yersinia infections. Rodents also play a role in the transmission of viruses such as avian influenza virus, avian paramyxovirus 1, avian gammacoronavirus or infectious bursal disease virus, but knowledge of these pathogens is very limited and requires further research to expand it.

Genetic Evolution Characteristics of Genotype G57 Virus, A Dominant Genotype of H9N2 Avian Influenza Virus

This study aimed to investigate the genetic evolution of the H9N2 avian influenza virus (AIV). Whole genome phylogenetic trees were constructed based on 306 H9N2 avian influenza strains collected in China from 2014 to 2019. The results showed that eight gene sequences were clustered separately according to their dominant clades, and a total of 10 genotypes were identified (seven of which were novel types). Among them, G57 genotype was confirmed as the most prevalent genotype with a frequency of 94%. In China, the G57 genotype of H9N2 first emerged in 2007, and then became the most common genotype in 2013. Therefore, the nucleotide substitution rates of G57 genotype in HA and NA genes collected from 2007 to 2019 were estimated, and the positive selection pressure sites in the same data set were measured. Taking 2013 as the boundary, the time period was divided into two periods: 2007-2012 and 2013-2019. From 2007 to 2012, multiple genotypes coexisted and could bear the pressures from both nature and environment; while G57 genotype was still in the adaptation stage, subjected to less selection pressure and in the process of slow evolution. However, from 2013 to 2019, G57 became the dominant genotype, and most of the external pressure reacted on it. Moreover, G57 genotype showed better adaptability than other genotypes. From 2013 to 2019, the nucleotide substitution rates of the HA gene were increased, and the positive selection pressures on HA and NA genes were stronger compared to those from 2007 to 2012. To sum up, the absolutely dominant G57 genotype exhibited a relatively constant genotype frequency and experienced adaptive evolution and natural selection simultaneously during the monitoring period. Therefore, urgent attention and diligent surveillance of H9N2 avian influenza virus are becoming increasingly important.

Avian Influenza A Virus Associations in Wild, Terrestrial Mammals: A Review of Potential Synanthropic Vectors to Poultry Facilities

The potential role of wild mammals in the epidemiology of influenza A viruses (IAVs) at the farm-side level has gained increasing consideration over the past two decades. In some instances, select mammals may be more likely to visit riparian areas (both close and distant to farms) as well as poultry farms, as compared to traditional reservoir hosts, such as waterfowl. Of significance, many mammalian species can successfully replicate and shed multiple avian IAVs to high titers without prior virus adaptation and often can shed virus in greater quantities than synanthropic avian species. Within this review, we summarize and discuss the potential risks that synanthropic mammals could pose by trafficking IAVs to poultry operations based on current and historic literature.

Chronic exposure to arsenite enhances influenza virus infection in cultured cells

Arsenic is a ubiquitous environmental toxicant that has been associated with human respiratory diseases. In humans, arsenic exposure has been associated with increased risk of respiratory infection. Considering the existing epidemiological evidence and the well-established impact of arsenic on epithelial cell biology, we posited that the effect of arsenic exposure in epithelial cells could enhance viral infection. In this study, we characterized influenza virus A/WSN/33 (H1N1) infection in Madin-Darby Canine Kidney (MDCK) cells chronically exposed to low levels of sodium arsenite (75 ppb). We observed a 27.3-fold increase in viral matrix (M2) protein (24 hours postinfection [p.i.]), a 1.35-fold increase in viral mRNA levels, and a 126% increase in plaque area in arsenite-exposed MDCK cells (48 hours p.i.). Arsenite exposure resulted in 114% increase in virus attachment-positive cells (2 hours p.i.) and 224% increase in α-2,3 sialic acid-positive cells. Interestingly, chronic exposure to arsenite reduced the effect of the antiviral drug, oseltamivir in MDCK cells. We also found that exposure to sodium arsenite resulted in a 4.4-fold increase in viral mRNA levels and significantly increased cytotoxicity in influenza A/Udorn/72 (H3N2) infected BEAS-2B cells. This study suggests that chronic arsenite exposure could result in enhanced influenza infection in epithelial cells, and that this may be mediated through increased sialic acid binding. Finally, the decreased effectiveness of the anti-influenza drug, oseltamivir, in arsenite-exposed cells raises substantial public health concerns if this effect translates to arsenic-exposed, influenza-infected people.

Evidence of Influenza A in Wild Norway Rats (Rattus norvegicus) in Boston, Massachusetts

Influenza A virus (IAV) is known to circulate among human and animal reservoirs, yet there are few studies that address the potential for urban rodents to carry and shed IAV. Rodents are often used as influenza models in the lab, but the few field studies that have looked for evidence of IAV in rodents have done so primarily in rural areas following outbreaks of IAV in poultry. This study sought to assess the prevalence of IAV recovered from wild Norway rats in a dense urban location (Boston). To do this, we sampled the oronasal cavity, paws, and lungs of Norway rats trapped by the City of Boston's Inspectional Services from December 2016 to September 2018. All samples were screened by real-time, reverse transcriptase PCR targeting the conserved IAV matrix segment. A total of 163 rats were trapped, 18 of which (11.04%) were RT-PCR positive for IAV in either oronasal swabs (9), paw swabs (9), both (2), or lung homogenates (2). A generalized linear model indicated that month and geographic location were correlated with IAV-positive PCR status of rats. A seasonal trend in IAV-PCR status was observed with the highest prevalence occurring in the winter months (December-January) followed by a decline over the course of the year, reaching its lowest prevalence in September. Sex and weight of rats were not significantly associated with IAV-PCR status, suggesting that rodent demography is not a primary driver of infection. This pilot study provides evidence of the need to further investigate the role that wild rats may play as reservoirs or mechanical vectors for IAV circulation in urban environments across seasons.

Effects of closing and reopening live poultry markets on the epidemic of human infection with avian influenza A virus

Live poultry markets (LPMs) are crucial places for human infection of influenza A (H7N9 virus). In Yangtze River Delta, LPMs were closed after the outbreak of human infection with avian influenza A (H7N9) virus, and then reopened when no case was found. Our purpose was to quantify the effect of LPMs' operations in this region on the transmission of influenza A (H7N9) virus. We obtained information about dates of symptom onset and locations for all human influenza A (H7N9) cases reported from Shanghai, Jiangsu and Zhejiang provinces by May 31, 2014, and acquired dates of closures and reopening of LPMs from official media. A two-phase Bayesian model was fitted by Markov Chain Monte Carlo methods to process the spatial and temporal influence of human cases. A total of 235 cases of influenza A (H7N9) were confirmed in Shanghai, Jiangsu and Zhejiang by May 31, 2014. Using these data, our analysis showed that, after LPM closures, the influenza A (H7N9) outbreak disappeared within two weeks in Shanghai, one week in Jiangsu, and one week in Zhejiang, respectively. Local authorities reopened LPMs when there was no outbreak of influenza A (H7N9), which did not lead to reemergence of human influenza A (H7N9). LPM closures were effective in controlling the H7N9 outbreak. Reopening of LPM in summer did not increase the risk of human infection with H7N9. Our findings showed that LPMs should be closed immediately in areas where the H7N9 virus is confirmed in LPM. When there is no outbreak of H7N9 virus, LPMs can be reopened to satisfy the Chinese traditional culture of buying live poultry. In the long term, local authorities should take a cautious attitude in permanent LPM closure.

Susceptibility to and transmission of H5N1 and H7N1 highly pathogenic avian influenza viruses in bank voles (Myodes glareolus)

The study of influenza type A (IA) infections in wild mammals populations is a critical gap in our knowledge of how IA viruses evolve in novel hosts that could be in close contact with avian reservoir species and other wild animals. The aim of this study was to evaluate the susceptibility to infection, the nasal shedding and the transmissibility of the H7N1 and H5N1 highly pathogenic avian influenza (HPAI) viruses in the bank vole (Myodes glareolus), a wild rodent common throughout Europe and Asia. Two out of 24 H5N1-infected voles displayed evident respiratory distress, while H7N1-infected voles remained asymptomatic. Viable virus was isolated from nasal washes collected from animals infected with both HPAI viruses, and extra-pulmonary infection was confirmed in both experimental groups. Histopathological lesions were evident in the respiratory tract of infected animals, although immunohistochemistry positivity was only detected in lungs and trachea of two H7N1-infected voles. Both HPAI viruses were transmitted by direct contact, and seroconversion was confirmed in 50% and 12.5% of the asymptomatic sentinels in the H7N1 and H5N1 groups, respectively. Interestingly, viable virus was isolated from lungs and nasal washes collected from contact sentinels of both groups. The present study demonstrated that two non-rodent adapted HPAI viruses caused asymptomatic infection in bank voles, which shed high amounts of the viruses and were able to infect contact voles. Further investigations are needed to determine whether bank voles could be involved as silent hosts in the transmission of HPAI viruses to other mammals and domestic poultry.

Exploring sialic acid receptors-related infection behavior of avian influenza virus in human bronchial epithelial cells by single-particle tracking

Human respiratory tract epithelial cells are the portals of human infection with influenza viruses. However, the infection pathway of individual avian influenza viruses in human respiratory cells remains poorly reported so far. The single-particle tracking technique (SPT) is a powerful tool for studying the transport mechanism of biomolecules in live cells. In this work, we use quantum dots to label avian influenza H9N2 virus and elaborate on the infection mechanism of the virus in human bronchial epithelial (HBE) cells using a three-dimensional SPT technique. We have found that the H9N2 virus can infect HBE cells directly and the virus infection follows an actin filament- and microtubule-dependent process with a three-stage pattern. The transport behaviors show a high degree of consistency between the sialic acid receptors and the influenza virus. Real-time SPT provides dynamic evidence of the sialic acid receptors-related infection behavior of the avian influenza virus in live cells. The study of the influence of sialic acid receptors on virus infection may contribute to a better understanding of the cross-species transmission of the avian influenza virus.

Origin and characteristics of internal genes affect infectivity of the novel avian-origin influenza A (H7N9) virus

Background

Human infection with a novel avian-origin influenza A (H7N9) virus occurred continuously in China during the first half of 2013, with high infectivity and pathogenicity to humans. In this study, we investigated the origin of internal genes of the novel H7N9 virus and analyzed the relationship between internal genes and infectivity of the virus.

Methodology and Principal findings

We tested the environmental specimens using real-time RT-PCR assays and isolated five H9N2 viruses from specimens that were positive for both H7 and H9. Results of recombination and phylogeny analysis, performed based on the entire sequences of 221 influenza viruses, showed that one of the Zhejiang avian H9N2 isolates, A/environment/Zhejiang/16/2013, shared the highest identities on the internal genes with the novel H7N9 virus A/Anhui/1/2013, ranging from 98.98% to 100%. Zhejiang avian H9N2 isolates were all reassortant viruses, by acquiring NS gene from A/chicken/Dawang/1/2011-like viruses and other five internal genes from A/brambling/Beijing/16/2012-like viruses. Compared to A/Anhui/1/2013 (H7N9), the homology on the NS gene was 99.16% with A/chicken/Dawang/1/2011, whereas only 94.27-97.61% with A/bramnling/Beijing/16/2012-like viruses. Analysis on the relationship between internal genes and the infectivity of novel H7N9 viruses were performed by comparing amino acid sequences with the HPAI H5N1 viruses, the H9N2 and the earlier H7N9 avian influenza viruses. There were nine amino acids on the internal genes found to be possibly associated with the infectivity of the novel H7N9 viruses.

Conclusions

These findings indicate that the internal genes, sharing the highest similarities with A/environment/Zhejiang/16/2013-like (H9N2) viruses, may affect the infectivity of the novel H7N9 viruses.

Proteomic analysis at the subcellular level for host targets against influenza A virus (H1N1)

Influenza viruses (IVs) trigger a series of intracellular signaling events and induce complex cellular responses from the infected host cell. Accumulating evidence suggests that host cell proteins play an essential role in viral propagation and represent novel antiviral therapeutic targets. Subcellular proteomic technology provides a method for understanding regional differences at the protein level. The present study, which utilized subcellular proteomic technology, aimed to identify host cell proteins involved in influenza virus (HIN1) infection. Two-dimensional gel electrophoresis (2-DE) combined with mass spectrum (MS) was performed on protein extracts from the nuclei, cytoplasm, and mitochondria of infected and control human lung epithelial cells (A549). In total, 112 differentially expressed protein molecules were identified; 80 protein spots were successfully validated using MS. The differential expression of ISG15, MIF, PDCD5, and UCHL1 was confirmed by western blot. Furthermore, antisense oligodeoxyribonucleotide (ODN) targeting ISG15, MIF, PDCD5, and UCHL1 significantly mitigated HIN1 propagation, cytopathic effects, vRNA by RT-qPCR, and rescued cell viability in A549 cells. Taken together, the differentially expressed proteins identified in this study might provide novel targets for anti-influenza drug development.

The genesis and source of the H7N9 influenza viruses causing human infections in China

A novel H7N9 influenza A virus first detected in March 2013 has since caused more than 130 human infections in China, resulting in 40 deaths. Preliminary analyses suggest that the virus is a reassortant of H7, N9 and H9N2 avian influenza viruses, and carries some amino acids associated with mammalian receptor binding, raising concerns of a new pandemic. However, neither the source populations of the H7N9 outbreak lineage nor the conditions for its genesis are fully known. Using a combination of active surveillance, screening of virus archives, and evolutionary analyses, here we show that H7 viruses probably transferred from domestic duck to chicken populations in China on at least two independent occasions. We show that the H7 viruses subsequently reassorted with enzootic H9N2 viruses to generate the H7N9 outbreak lineage, and a related previously unrecognized H7N7 lineage. The H7N9 outbreak lineage has spread over a large geographic region and is prevalent in chickens at live poultry markets, which are thought to be the immediate source of human infections. Whether the H7N9 outbreak lineage has, or will, become enzootic in China and neighbouring regions requires further investigation. The discovery here of a related H7N7 influenza virus in chickens that has the ability to infect mammals experimentally, suggests that H7 viruses may pose threats beyond the current outbreak. The continuing prevalence of H7 viruses in poultry could lead to the generation of highly pathogenic variants and further sporadic human infections, with a continued risk of the virus acquiring human-to-human transmissibility.

Connecting the study of wild influenza with the potential for pandemic disease

Continuing outbreaks of pathogenic (H5N1) and pandemic (SOIVH1N1) influenza have underscored the need to understand the origin, characteristics, and evolution of novel influenza A virus (IAV) variants that pose a threat to human health. In the last 4-5years, focus has been placed on the organization of large-scale surveillance programs to examine the phylogenetics of avian influenza virus (AIV) and host-virus relationships in domestic and wild animals. Here we review the current gaps in wild animal and environmental surveillance and the current understanding of genetic signatures in potentially pandemic strains.

Avian influenza and ban on overnight poultry storage in live poultry markets, Hong Kong

We analyzed ≈12 years of surveillance data on avian influenza in Hong Kong live poultry markets. A ban on keeping live poultry overnight in these markets reduced virus isolation rates by 84% in chickens (p = 0.006) and 100% (p = 0.01) in minor poultry.

Two-dimensional antigenic dendrogram and phylogenetic tree of avian influenza virus H5N1

The hemagglutination-inhibition (HI) titers of a panel of 25 mouse monoclonal antibodies (MAbs) against 44 isolates of highly pathogenic avian influenza virus H5N1 were determined. A two-dimensional antigenic dendrogram was constructed by hierarchical clustering of HI titers. Viruses with similar reactivity patterns were clustered horizontally, whereas MAbs were clustered vertically. In this 2-D dendrogram, with 40% similarity as a cut-off, four virus clusters and four MAbs clusters were identified. A phylogenetic tree based on the deduced amino acid sequence of the hemagglutinin gene of tested viruses was constructed and its topology was compared to the antigenic dendrogram. Interestingly, viruses with high genetic homology in the phylogenetic tree also had high similarity in their reactivity patterns, as indicated by their relatedness in the tree and close clustering in the dendrogram, respectively. However, the reverse and the converse were also true. Of the five pairs of viruses in the dendrogram with bootstrap values higher than 75, four pairs were in concordance with their genetic relatedness. However, one pair contained viruses belong to two distinct genetic clades. These results were discussed in the context of antigenic variation, genetic polymorphism, and the potential application of MAbs in antigenic analysis.

Low-pathogenic avian influenza viruses in wild house mice

BACKGROUND

Avian influenza viruses are known to productively infect a number of mammal species, several of which are commonly found on or near poultry and gamebird farms. While control of rodent species is often used to limit avian influenza virus transmission within and among outbreak sites, few studies have investigated the potential role of these species in outbreak dynamics.

METHODOLOGY/PRINCIPAL FINDINGS

We trapped and sampled synanthropic mammals on a gamebird farm in Idaho, USA that had recently experienced a low pathogenic avian influenza outbreak. Six of six house mice (Mus musculus) caught on the outbreak farm were presumptively positive for antibodies to type A influenza. Consequently, we experimentally infected groups of naïve wild-caught house mice with five different low pathogenic avian influenza viruses that included three viruses derived from wild birds and two viruses derived from chickens. Virus replication was efficient in house mice inoculated with viruses derived from wild birds and more moderate for chicken-derived viruses. Mean titers (EID(50) equivalents/mL) across all lung samples from seven days of sampling (three mice/day) ranged from 10(3.89) (H3N6) to 10(5.06) (H4N6) for the wild bird viruses and 10(2.08) (H6N2) to 10(2.85) (H4N8) for the chicken-derived viruses. Interestingly, multiple regression models indicated differential replication between sexes, with significantly (p<0.05) higher concentrations of avian influenza RNA found in females compared with males.

CONCLUSIONS/SIGNIFICANCE

Avian influenza viruses replicated efficiently in wild-caught house mice without adaptation, indicating mice may be a risk pathway for movement of avian influenza viruses on poultry and gamebird farms. Differential virus replication between males and females warrants further investigation to determine the generality of this result in avian influenza disease dynamics.

Distribution of sialic acid receptors and influenza A virus of avian and swine origin in experimentally infected pigs

Background

Pigs are considered susceptible to influenza A virus infections from different host origins because earlier studies have shown that they have receptors for both avian (sialic acid-alpha-2,3-terminal saccharides (SA-alpha-2,3)) and swine/human (SA-alpha-2,6) influenza viruses in the upper respiratory tract. Furthermore, experimental and natural infections in pigs have been reported with influenza A virus from avian and human sources.

Methods

This study investigated the receptor distribution in the entire respiratory tract of pigs using specific lectins Maackia Amurensis (MAA) I, and II, and Sambucus Nigra (SNA). Furthermore, the predilection sites of swine influenza virus (SIV) subtypes H1N1 and H1N2 as well as avian influenza virus (AIV) subtype H4N6 were investigated in the respiratory tract of experimentally infected pigs using immunohistochemical methods.

Results

SIV antigen was widely distributed in bronchi, but was also present in epithelial cells of the nose, trachea, bronchioles, and alveolar type I and II epithelial cells in severely affected animals. AIV was found in the lower respiratory tract, especially in alveolar type II epithelial cells and occasionally in bronchiolar epithelial cells. SA-alpha-2,6 was the predominant receptor in all areas of the respiratory tract with an average of 80-100% lining at the epithelial cells. On the contrary, the SA-alpha-2,3 was not present (0%) at epithelial cells of nose, trachea, and most bronchi, but was found in small amounts in bronchioles, and in alveoli reaching an average of 20-40% at the epithelial cells. Interestingly, the receptor expression of both SA-alpha-2,3 and 2,6 was markedly diminished in influenza infected areas compared to non-infected areas.

Conclusions

A difference in predilection sites between SIV and AIV virus was found, and this difference was in accordance with the distribution of the SA-alpha-2,6 and SA-alpha-2,3 receptor, respectively. The results indicated that the distribution of influenza A virus receptors in pigs are similar to that of humans and therefore challenge the theory that the pig acts as a mixing vessel between human and avian influenza viruses. Furthermore, it was shown that AIV prefers to infect alveolar type II epithelial cells in pigs. This corresponds with findings in humans emphasising the resemblance between the two species.

Impact of the implementation of rest days in live bird markets on the dynamics of H5N1 highly pathogenic avian influenza

Live bird markets (LBMs) act as a network 'hub' and potential reservoir of infection for domestic poultry. They may therefore be responsible for sustaining H5N1 highly pathogenic avian influenza (HPAI) virus circulation within the poultry sector, and thus a suitable target for implementing control strategies. We developed a stochastic transmission model to understand how market functioning impacts on the transmission dynamics. We then investigated the potential for rest days-periods during which markets are emptied and disinfected-to modulate the dynamics of H5N1 HPAI within the poultry sector using a stochastic meta-population model. Our results suggest that under plausible parameter scenarios, HPAI H5N1 could be sustained silently within LBMs with the time spent by poultry in markets and the frequency of introduction of new susceptible birds' dominant factors determining sustained silent spread. Compared with interventions applied in farms (i.e. stamping out, vaccination), our model shows that frequent rest days are an effective means to reduce HPAI transmission. Furthermore, our model predicts that full market closure would be only slightly more effective than rest days to reduce transmission. Strategies applied within markets could thus help to control transmission of the disease.

Full genomic amplification and subtyping of influenza A virus using a single set of universal primers

Influenza A virus has eight-segmented RNA molecules as a genome and, among all strains of the virus, both ends of each segment have 13 and 12 nucleotide sequences conserved. In the present study, a simple RT-PCR method to amplify all eight segments of the virus and determine the HA and NA subtype using a single primer set based on the conserved terminal sequences has been established. This method is also capable of detecting subgenomic defective interfering RNA of the influenza A virus. Since the primers used here cope with each and every RNA segment of influenza A virus, this simple RT-PCR method is valuable not only for cloning each gene of the virus, but also for identifying subtypes, including subtypes other than 16 HA and 9 NA subtypes.

Knowledge and anticipated attitudes of the community about bird flu outbreak in Turkey, 2007-2008: a survey-based descriptive study

OBJECTIVE

To determine factors associated with knowledge and anticipated attitudes to a foreseen avian influenza outbreak in a high-risk population from a Turkish remote region.

METHODS

A random, cross-sectional face-to-face survey of 1,046 Turkish adults.

RESULTS

The proportion of participants concerned about contracting the virus was significantly lower amongst the less educated and rural located respondents. Significantly more rural than urban located participants declared not complying with quarantine policies and not handing out their poultry in case of an influenza outbreak. Factors associated with protective behaviours were higher level of education, urban location, not performing backyard farming of poultry, and preferring ready-to-eat products.

CONCLUSIONS

Preparedness against bird flu endemic in remote regions could be hindered by factors, such as low levels of education and economic dependence on small-scale backyard farming. The baseline data collected in this survey will be useful in monitoring changes over time in the population's perceptions of threat, and its attitude towards compliance with specific public health recommendations.

Host immune and apoptotic responses to avian influenza virus H9N2 in human tracheobronchial epithelial cells

The avian influenza virus H9N2 subtype has circulated in wild birds, is prevalent in domestic poultry, and has successfully crossed the species boundary to infect humans. Phylogenetic analyses showed that viruses of this subtype appear to have contributed to the generation of highly pathogenic H5N1 viruses. Little is known about the host responses to H9N2 viruses in human airway respiratory epithelium, the primary portal for viral infection. Using an apically differentiated primary human tracheobronchial epithelial (TBE) culture, we examined host immune responses to infection by an avian H9N2 virus, in comparison with a human H9N2 isolate. We found that IFN-β was the prominent antiviral component, whereas interferon gamma-induced protein 10 kDa (IP-10), chemokine (C-C motif) ligand (CCL)-5 and TNF-α may be critical in proinflammatory responses to H9N2 viruses. In contrast, proinflammatory IL-1β, IL-8, and even IL-6 may only play a minor role in pathogenicity. Apparently Toll-like receptor (TLR)-3, TLR-7, and melanoma differentiation-associated gene 5 (MDA-5) contributed to the innate immunity against the H9N2 viruses, and MDA-5 was important in the induction of IFN-β. We showed that the avian H9N2 virus induced apoptosis through the mitochondria/cytochrome c-mediated intrinsic pathway, in addition to the caspase 8-mediated extrinsic pathway, as evidenced by the cytosolic presence of active caspase 9 and cytochrome c, independent of truncated BH3 interacting domain death agonist (Bid) activation. Further, we demonstrated that FLICE-like inhibitory protein (FLIP), an apoptotic dual regulator, and the p53-dependent Bcl-2 family members, Bax and Bcl-x(s), appeared to be involved in the regulation of extrinsic and intrinsic apoptotic pathways, respectively. The findings in this study will further our understanding of host defense mechanisms and the pathogenesis of H9N2 influenza viruses in human respiratory epithelium.

Molecular events leading to the creation of a pandemic influenza virus

Influenza A virus is a potent pathogen of annual respiratory illness with huge potential of causing occasional pandemics of catastrophic consequences. In April 2009, a novel, swine-origin influenza A H1N1/09 virus was identified in Mexico which continued to spread globally. This unique virus emerged from an avian, human, Eurasian swine viral strain and a North American swine strain belonging to the lineage of the 1930 swine virus. Till date H1N1/09 pandemic has been relatively mild and lacks the previously described molecular markers of influenza A pathogenicity and transmissibility. In this review, we will discuss the molecular and antigenic determinants of this virus and its designation as a low pathogenic strain, which carries the potential to develop into a devastating strain with subsequent mutations and reassortments.

Advances in the molecular based techniques for the diagnosis and characterization of avian influenza virus infections

There have been remarkable advances in the molecular diagnosis and characterization of avian influenza virus infections in domestic poultry and free-living birds in the past two decades. Rapid pathotyping became possible with the recognition that the amino acid sequence of the connecting peptide of the haemagglutinin precursor, HA(0), is a major virulence determinant for H5 and H7 subtype viruses. This in turn resulted in nucleic acid sequencing as a relatively routine method for identifying highly pathogenic avian influenza virus isolates. Subsequent development of diagnostic methods based on reverse transcription-polymerase chain reaction (RT-PCR), real-time RT-PCR, nucleic acid sequence-based amplification and loop-mediated isothermal amplification has made the rapid detection of group A influenza and H5 and H7 subtype viruses possible. Further development of these assay platforms has enabled the specific detection of H5N1 Eurasian subtype viruses and the inference of their HA(0) cleavage sites. Identification of additional virulence determinants of influenza A viruses for birds and mammals will allow the emerging area of microarray technology to further extend our understanding of their ecology, epidemiology and pathogenesis.

Qualitative detection of avian influenza A (H5N1) viruses: a comparative evaluation of four real-time nucleic acid amplification methods

The aim of this study was to determine the performance of real-time amplification based methods - NASBA, TaqMan, RT-FRET, and RT-PCR LUXtrade mark formats - for the detection of influenza A (H5N1) virus RNA. In an analysis of 54 samples obtained from a range of animal species in Thailand during the period 2003-2006, results showed that the NASBA (H5=98.2%, N1=96.3%), TaqMan (H5=98.2%, N1=96.3%) and FRET (H5=98.2%, N1=96.3%) had significantly higher rates of positive detection than LUX (H5=94.4%, N1=50.0%; P<0.001) for influenza A, H5 and N1 isolates. There were no false-positive results from any methods used in the negative-control group of samples. The limits of analytical detection were at least 10copies/reaction in real-time NASBA and LUX assays, while FRET and TaqMan assay appeared to be less sensitive at > or =100copies/reaction. The assays were relatively specific without cross-reactivity to a number of other influenza strains or viral pathogens. In conclusion, our study demonstrated that real-time NASBA, TaqMan and FRET assays can be used to detect influenza A (H5N1) from a wide range of hosts, and be specific for H5N1 samples obtained during different outbreaks (2003-2006). All assays provided the benefit of rapid influenza H5N1 identification for early diagnosis, in the range of hours, and they are well suited to high throughput analyses.

Avian Influenza and Pandemic Influenza Preparedness in Hong Kong

Avian influenza A H5N1 continues to be a major threat to global public health as it is a likely candidate for the next influenza pandemic. To protect public health and avert potential disruption to the economy, the Hong Kong Special Administrative Region Government has committed substantial effort in preparedness for avian and pandemic influenza. Public health infrastructures for emerging infectious diseases have been developed to enhance command, control and coordination of emergency response. Strategies against avian and pandemic influenza are formulated to reduce opportunities for human infection, detect pandemic influenza timely, and enhance emergency preparedness and response capacity. Key components of the pandemic response include strengthening disease surveillance systems, updating legislation on infectious disease prevention and control, enhancing traveller health measures, building surge capacity, maintaining adequate pharmaceutical stockpiles, and ensuring business continuity during crisis. Challenges from avian and pandemic influenza are not to be underestimated. Implementing quarantine and social distancing measures to contain or mitigate the spread of pandemic influenza is problematic in a highly urbanised city like Hong Kong as they involved complex operational and ethical issues. Sustaining effective risk communication campaigns during inter-pandemic times is another challenge. Being a member of the global village, Hong Kong is committed to contributing its share of efforts and collaborating with health authorities internationally in combating our common public health enemy. Key words: Emergency response, Infections, Surveillance, Quarantine

Poultry drinking water used for avian influenza surveillance

Samples of drinking water from poultry cages, which can be collected conveniently and noninvasively, provide higher rates of influenza (H9N2) virus isolation than do samples of fecal droppings. Studies to confirm the usefulness of poultry drinking water for detecting influenza (H5N1) should be conducted in disease-endemic areas.

H9N2 influenza viruses from Israeli poultry: a five-year outbreak

Since 2000, hundreds of H9N2 viruses have been isolated from all types of domestic birds. Although H9N2 is a low-pathogenicity virus, disease has been observed in all types of poultry in the field. Clinical signs ranged from very mild disease to high morbidity and mortality when the virus was associated with a secondary pathogen. Because of the wide range of the virus and the great losses it caused, initially a local vaccination program was implemented, but mass vaccination was quickly authorized. A local strain, isolated in 2002 was selected and is currently in use as an inactivated vaccine. An intensive operation is in progress to characterize the isolates. Several genes (hemagglutinin [HA], neuraminidase, nonstructural protein, nucleoprotein, and matrix) were sequenced, revealing three main groups: the first group included two isolates from 2000, the second group included isolates from 2001 to the beginning of 2003, and the third group included all isolates from 2003 to date. The differences between the second and third groups, in a part of the HA gene, ranged from 3.49% to 6.97% (average 4.57%) of the nucleotides. Similar differences were recorded in the other tested genes. These data could indicate the probable introduction of distinct progenitor viruses into the Israeli poultry population. Furthermore, sequencing of the HA protein of some Israeli isolates revealed the presence of L216 in the binding site; this finding was typical of the H9N2 viruses isolated from humans, which raises the possibility of an influence on host specificity and virulence.

Pathobiology of H9N2 avian influenza virus in Japanese quail (Coturnix coturnix japonica)

Clinical signs, serologic response, viral contents of the trachea and intestine, and histopathological and ultrastructural changes of the tracheal epithelium of Japanese quail experimentally infected with field isolate of H9N2 avian influenza were studied. Vaccinated and unvaccinated quail were inoculated with 10(6.3) 50% embryo infectious dose/bird of A/ chicken/Iran/SH-110/99 (H9N2) virus via nasal inoculation. Clinical signs such as depression, ruffled feathers, diarrhea, and nasal and eye discharges were observed 6 days postinfection (PI). No mortality was observed; however, there was reduction in feed and water consumption and egg production. However, the serologic response of vaccinated challenged and unvaccinated challenged birds was not significantly different. Unvaccinated challenged quail showed more severe histopathologic reaction in their lungs and trachea. Hyperemia, edema, infiltration of inflammatory cells, and deciliation and sloughing of the tracheal epithelium were observed. Ultrastructural study showed dilatation of endoplasmic reticulum and degeneration of Golgi apparatus and cilia of the tracheal lining cells of respiratory epithelium.

Avian and swine influenza viruses: our current understanding of the zoonotic risk

The introduction of swine or avian influenza (AI) viruses in the human population can set the stage for a pandemic, and many fear that the Asian H5N1 AI virus will become the next pandemic virus. This article first compares the pathogenesis of avian, swine and human influenza viruses in their natural hosts. The major aim was to evaluate the zoonotic potential of swine and avian viruses, and the possible role of pigs in the transmission of AI viruses to humans. Cross-species transfers of swine and avian influenza to humans have been documented on several occasions, but all these viruses lacked the critical capacity to spread from human-to-human. The extreme virulence of H5N1 in humans has been associated with excessive virus replication in the lungs and a prolonged overproduction of cytokines by the host, but there remain many questions about the exact viral cell and tissue tropism. Though pigs are susceptible to several AI subtypes, including H5N1, there is clearly a serious barrier to infection of pigs with such viruses. AI viruses frequently undergo reassortment in pigs, but there is no proof for a role of pigs in the generation of the 1957 or 1968 pandemic reassortants, or in the transmission of H5N1 or other wholly avian viruses to humans. The major conclusion is that cross-species transmission of influenza viruses per se is insufficient to start a human influenza pandemic and that animal influenza viruses must undergo dramatic but largely unknown genetic changes to become established in the human population.

Development of an internal positive control for rapid diagnosis of avian influenza virus infections by real-time reverse transcription-PCR with lyophilized reagents

We developed an internal positive control (IPC) RNA to help ensure the accuracy of the detection of avian influenza virus (AIV) RNA by reverse transcription (RT)-PCR and real-time RT-PCR (RRT-PCR). The IPC was designed to have the same binding sites for the forward and reverse primers of the AIV matrix gene as the target amplicon, but it had a unique internal sequence used for the probe site. The amplification of the viral RNA and the IPC by RRT-PCR were monitored with two different fluorescent probes in a multiplex format, one specific for the AIV matrix gene and the other for the IPC. The RRT-PCR test was further simplified with the use of lyophilized bead reagents for the detection of AIV RNA. The RRT-PCR with the bead reagents was more sensitive than the conventional wet reagents for the detection of AIV RNA. The IPC-based RRT-PCR detected inhibitors in blood, kidney, lungs, spleen, intestine, and cloacal swabs, but not allantoic fluid, serum, or tracheal swabs The accuracy of RRT-PCR test results with the lyophilized beads was tested on cloacal and tracheal swabs from experimental birds inoculated with AIV and compared with virus isolation (VI) on embryonating chicken eggs. There was 97 to 100% agreement of the RRT-PCR test results with VI for tracheal swabs and 81% agreement with VI for cloacal swabs, indicating a high level of accuracy of the RRT-PCR assay. The same IPC in the form of armored RNA was also used to monitor the extraction of viral RNA and subsequent detection by RRT-PCR.

Comparison of the replication of influenza A viruses in Chinese ring-necked pheasants and chukar partridges

We investigated the replication and transmission of avian influenza A viruses in two species thought to be intermediate hosts in the spread of influenza A viruses in live poultry markets: Chinese ring-necked pheasants and chukar partridges. All 15 hemagglutinin subtypes replicated in pheasants, and most subtypes transmitted to naïve contact pheasants, primarily via the fecal-oral route. Many viruses were shed from the gastrointestinal tract of experimentally inoculated pheasants for 14 days or longer. Virus was isolated from the cloacal swabs of one contact pheasant for an unprecedented 45 days. Chukar partridges were less susceptible to infection with avian influenza viruses. The viruses that replicated in chukar partridges were isolated for 7 days after experimental inoculation, predominantly from the respiratory tract. We detected high neutralizing antibody titers with correspondingly low levels of serum hemagglutination inhibition antibody titers in pheasants and chukar partridges when chicken red blood cells were used in serological analyses. When horse erythrocytes were used, antibody titers were comparable to those obtained by using the neutralization assay. More importantly, the results suggested that pheasants can serve as a reservoir of influenza virus. Because of their continuous asymptomatic infection and longer stay in the markets, pheasants are ideal "carriers" of influenza A viruses. Their continued presence in live markets contributes to the perpetuation and genetic interaction of influenza viruses there. On the basis of our findings, it does not make good sense to ban quail but not pheasants from the live markets.

Prevalence of enzootic simian viruses among urban performance monkeys in Indonesia

Animal reservoirs are the most important sources of emerging infectious diseases that threaten human populations. Global travel and tourism bring ever-increasing numbers of humans into contact with animals, increasing the likelihood of cross species transmission of infectious agents. Non-human primates come into contact with humans in a variety of contexts and may harbor infectious agents with zoonotic potential. We investigated the prevalence of infection with enzootic simian viruses among 20 urban performance monkeys (Macaca fascicularis) in Jakarta, Indonesia. This report documents for the first time evidence of infection with four simian viruses in urban performance monkeys. Simian foamy virus was detected by PCR in 52.9% of the macaques. Antibodies to simian retrovirus were detected in 10.5% of the macaques. Antibodies to Cercopithecine Herpesvirus 1, were detected in 5.3% of the macaques. Similarly, antibodies to simian T-cell lymphotropic virus were detected in 5.3% of the macaques. No evidence of infection with simian immunodeficiency virus was detected in these macaques. These results suggest that urban performance monkeys are a reservoir for enzootic simian viruses known to be capable of infecting humans.

Human disease from influenza A (H5N1), Thailand, 2004

Direct contact with sick poultry, young age, pneumonia and lymphopenia, and acute respiratory distress syndrome should prompt specific laboratory testing for H5 influenza.

Influenza A (H5N1) is endemic in poultry across much of Southeast Asia, but limited information exists on the distinctive features of the few human cases. In Thailand, we instituted nationwide surveillance and tested respiratory specimens by polymerase chain reaction and viral isolation. From January 1 to March 31, 2004, we reviewed 610 reports and identified 12 confirmed and 21 suspected cases. All 12 confirmed case-patients resided in villages that experienced abnormal chicken deaths, 9 lived in households whose backyard chickens died, and 8 reported direct contact with dead chickens. Seven were children <14 years of age. Fever preceded dyspnea by a median of 5 days, and lymphopenia significantly predicted acute respiratory distress syndrome development and death. Among hundreds of thousands of potential human cases of influenza A (H5N1) in Asia, a history of direct contact with sick poultry, young age, pneumonia and lymphopenia, and progression to acute respiratory distress syndrome should prompt specific laboratory testing for H5 influenza.

Standardization of a duplex RT-PCR for the detection of Influenza A and Newcastle disease viruses in migratory birds

Influenza A and Newcastle disease viruses are pathogens of social and economical importance known to be disseminated throughout the world by migratory birds. Many efforts have been made to control the introduction of these viruses into new environments, and complete world surveillance has yet to be achieved. Virus isolation and immunofluorescence techniques are time consuming, have inherent limited sensitivity and present a lack of host cells permissive universally to all Influenza A viruses. In this paper, the use of a duplex RT-PCR is described capable of sorting out any NDV and Influenza A virus strain simultaneously in oral and cloacal swab specimens. This method includes fluorescent detection of amplicons that provide accurate analysis of many DNA fragments within one base discrimination. Reference viruses were used for standardization of the assay and samples from wild-type viruses were screened, with four positive results for Influenza A detected in migratory birds captured in the state of Sao Paulo. This screening test can be considered a first step for further studies of these viruses circulating in avian species in Brazil, and hopefully will contribute to broaden the sample spectrum from wild birds, leading to a better understanding of these viruses and their participation in the southeastern region of the country.

Emerging infectious diseases: vulnerabilities, contributing factors and approaches

We live in an ever more connected global village linked through international travel, politics, economics, culture and human-human and human-animal interactions. The realization that the concept of globalization includes global exposure to disease-causing agents that were formerly confined to small, remote areas and that infectious disease outbreaks can have political, economic and social roots and effects is becoming more apparent. Novel infectious disease microbes continue to be discovered because they are new or newly recognized, have expanded their geographic range, have been shown to cause a new disease spectrum, have jumped the species barrier from animals to humans, have become resistant to antimicrobial agents, have increased in incidence or have become more virulent. These emerging infectious disease microbes may have the potential for use as agents of bioterrorism. Factors involved in the emergence of infectious diseases are complex and interrelated and involve all classifications of organisms transmitted in a variety of ways. In 2003, outbreaks of interest included severe acute respiratory syndrome, monkeypox and avian influenza. Information from the human genome project applied to microbial organisms and their hosts will provide new opportunities for detection, diagnosis, treatment, prevention, control and prognosis. New technology related not only to genetics but also to satellite and monitoring systems will play a role in weather, climate and the approach to environmental manipulations that influence factors contributing to infectious disease emergence and control. Approaches to combating emerging infectious diseases include many disciplines, such as animal studies, epidemiology, immunology, ecology, environmental studies, microbiology, pharmacology, other sciences, health, medicine, public health, nursing, cultural, political and social studies, all of which must work together. Appropriate financial support of the public health infrastructure including surveillance, prevention, communication, adherence techniques and the like will be needed to support efforts to address emerging infectious disease threats.

Active NF-kappaB signalling is a prerequisite for influenza virus infection

Influenza virus still poses a major threat to human health. Despite widespread vaccination programmes and the development of drugs targeting essential viral proteins, the extremely high mutation rate of influenza virus still leads to the emergence of new pathogenic virus strains. Therefore, it has been suggested that cellular cofactors that are essential for influenza virus infection might be better targets for antiviral therapy. It has previously been reported that influenza virus efficiently infects Epstein-Barr virus-immortalized B cells, whereas Burkitt's lymphoma cells are virtually resistant to infection. Using this cellular system, it has been shown here that an active NF-kappaB signalling pathway is a general prerequisite for influenza virus infection of human cells. Cells with low NF-kappaB activity were resistant to influenza virus infection, but became susceptible upon activation of NF-kappaB. In addition, blocking of NF-kappaB activation severely impaired influenza virus infection of otherwise highly susceptible cells, including the human lung carcinoma cell lines A549 and U1752 and primary human cells. On the other hand, infection with vaccinia virus was not dependent on an active NF-kappaB signalling pathway, demonstrating the specificity of this pathway for influenza virus infection. These results might be of major importance for both the development of new antiviral therapies and the understanding of influenza virus biology.

Responsiveness to a pandemic alert: use of reverse genetics for rapid development of influenza vaccines

BACKGROUND

In response to the emergence of severe infection capable of rapid global spread, WHO will issue a pandemic alert. Such alerts are rare; however, on Feb 19, 2003, a pandemic alert was issued in response to human infections caused by an avian H5N1 influenza virus, A/Hong Kong/213/03. H5N1 had been noted once before in human beings in 1997 and killed a third (6/18) of infected people. The 2003 variant seemed to have been transmitted directly from birds to human beings and caused fatal pneumonia in one of two infected individuals. Candidate vaccines were sought, but no avirulent viruses antigenically similar to the pathogen were available, and the isolate killed embryonated chicken eggs. Since traditional strategies of vaccine production were not viable, we sought to produce a candidate reference virus using reverse genetics.

METHODS

We removed the polybasic aminoacids that are associated with high virulence from the haemagglutinin cleavage site of A/Hong Kong/213/03 using influenza reverse genetics techniques. A reference vaccine virus was then produced on an A/Puerto Rico/8/34 (PR8) backbone on WHO-approved Vero cells. We assessed this reference virus for pathogenicity in in-vivo and in-vitro assays.

FINDINGS

A reference vaccine virus was produced in Good Manufacturing Practice (GMP)-grade facilities in less than 4 weeks from the time of virus isolation. This virus proved to be non-pathogenic in chickens and ferrets and was shown to be stable after multiple passages in embryonated chicken eggs.

INTERPRETATION

The ability to produce a candidate reference virus in such a short period of time sets a new standard for rapid response to emerging infectious disease threats and clearly shows the usefulness of reverse genetics for influenza vaccine development. The same technologies and procedures are currently being used to create reference vaccine viruses against the 2004 H5N1 viruses circulating in Asia.

Xenotransplantation and risks of zoonotic infections

The shortage of human organs and tissues for transplantation and the advances in immunology of rejection and in genetic engineering have renewed interest in xenotransplantation--the transplantation of animal organs, tissues or cells to humans. Clinical trials have involved the use of non-human primate, porcine, and bovine cells/tissues/organs. In recent years, research has focused mainly on pigs as donors (especially, pigs genetically engineered to carry some human genes). One of the major concerns in xenotransplantation is the risk of transmission of animal pathogens, particularly viruses, to recipients and the possible adaptation of such pathogens for human-to-human transmission. Porcine endogenous retroviruses (PERVs) have been of special concern because of their ability to infect human cells and because, at present, they cannot be removed from the source animal's genome. To date, retrospective studies of humans exposed to live porcine cells/tissues have not found evidence of infection with PERV but more extensive research is needed. This article reviews infectious disease risks associated with xenotransplantation, some measures for minimizing that risk, and microbiological diagnostic methods that may be used in the follow-up of xenotransplant recipients.