Infection studies with two highly pathogenic avian influenza strains (Vietnamese and Indonesian) in Pekin ducks (Anas platyrhynchos), with particular reference to clinical disease, tissue tropism and viral shedding

Automated quantification of avian influenza virus antigen in different organs

As immunohistochemistry is valuable for determining tissue and cell tropism of avian influenza viruses (AIV), but time-consuming, an artificial intelligence-based workflow was developed to automate the AIV antigen quantification. Organ samples from experimental AIV infections including brain, heart, lung and spleen on one slide, and liver and kidney on another slide were stained for influenza A-matrixprotein and analyzed with QuPath: Random trees algorithms were trained to identify the organs on each slide, followed by threshold-based quantification of the immunoreactive area. The algorithms were trained and tested on two different slide sets, then retrained on both and validated on a third set. Except for the kidney, the best algorithms for organ selection correctly identified the largest proportion of the organ area. For most organs, the immunoreactive area assessed following organ selection was significantly and positively correlated to a manually assessed semiquantitative score. In the validation set, intravenously infected chickens showed a generally higher percentage of immunoreactive area than chickens infected oculonasally. Variability between the slide sets and a similar tissue texture of some organs limited the ability of the algorithms to select certain organs. Generally, suitable correlations of the immunoreactivity data results were achieved, facilitating high-throughput analysis of AIV tissue tropism.

Evolution and expression of the duck TRIM gene repertoire

Tripartite motif (TRIM) proteins are involved in development, innate immunity, and viral restriction. TRIM gene repertoires vary between species, likely due to diversification caused by selective pressures from pathogens; however, this has not been explored in birds. We mined a de novo assembled transcriptome for the TRIM gene repertoire of the domestic mallard duck (Anas platyrhynchos), a reservoir host of influenza A viruses. We found 57 TRIM genes in the duck, which represent all 12 subfamilies based on their C-terminal domains. Members of the C-IV subfamily with C-terminal PRY-SPRY domains are known to augment immune responses in mammals. We compared C-IV TRIM proteins between reptiles, birds, and mammals and show that many C-IV subfamily members have arisen independently in these lineages. A comparison of the MHC-linked C-IV TRIM genes reveals expansions in birds and reptiles. The TRIM25 locus with related innate receptor modifiers is adjacent to the MHC in reptile and marsupial genomes, suggesting the ancestral organization. Within the avian lineage, both the MHC and TRIM25 loci have undergone significant TRIM gene reorganizations and divergence, both hallmarks of pathogen-driven selection. To assess the expression of TRIM genes, we aligned RNA-seq reads from duck tissues. C-IV TRIMs had high relative expression in immune relevant sites such as the lung, spleen, kidney, and intestine, and low expression in immune privileged sites such as in the brain or gonads. Gene loss and gain in the evolution of the TRIM repertoire in birds suggests candidate immune genes and potential targets of viral subversion.

Clade 2.3.4.4b H5N1 high pathogenicity avian influenza virus (HPAIV) from the 2021/22 epizootic is highly duck adapted and poorly adapted to chickens

The 2021/2022 epizootic of high pathogenicity avian influenza (HPAIV) remains one of the largest ever in the UK, being caused by a clade 2.3.4.4b H5N1 HPAIV. This epizootic affected more than 145 poultry premises, most likely through independent incursion from infected wild birds, supported by more than 1700 individual detections of H5N1 from wild bird mortalities. Here an H5N1 HPAIV, representative of this epizootic (H5N1-21), was used to investigate its virulence, pathogenesis and transmission in layer chickens and Pekin ducks, two species of epidemiological importance. We inoculated both avian species with decreasing H5N1-21 doses. The virus was highly infectious in ducks, with high infection levels and accompanying shedding of viral RNA, even in ducks inoculated with the lowest dose, reflecting the strong waterfowl adaptation of the clade 2.3.4.4 HPAIVs. Duck-to-duck transmission was very efficient, coupled with high environmental contamination. H5N1-21 was frequently detected in water sources, serving as likely sources of infection for ducks, but inhalable dust and aerosols represented low transmission risks. In contrast, chickens inoculated with the highest dose exhibited lower rates of infection compared to ducks. There was no evidence for experimental H5N1-21 transmission to any naive chickens, in two stocking density scenarios, coupled with minimal and infrequent contamination being detected in the chicken environment. Systemic viral dissemination to multiple organs reflected the pathogenesis and high mortalities in both species. In summary, the H5N1-21 virus is highly infectious and transmissible in anseriformes, yet comparatively poorly adapted to galliformes, supporting strong host preferences for wild waterfowl. Key environmental matrices were also identified as being important in the epidemiological spread of this virus during the continuing epizootic.

Genetic Determinants for Virulence and Transmission of the Panzootic Avian Influenza Virus H5N8 Clade 2.3.4.4 in Pekin Ducks

Waterfowl is the natural reservoir for avian influenza viruses (AIV), where the infection is mostly asymptomatic. In 2016, the panzootic high pathogenicity (HP) AIV H5N8 of clade 2.3.4.4B (designated H5N8-B) caused significant mortality in wild and domestic ducks, in stark contrast to the predecessor 2.3.4.4A virus from 2014 (designated H5N8-A). Here, we studied the genetic determinants for virulence and transmission of H5N8 clade 2.3.4.4 in Pekin ducks. While ducks inoculated with recombinant H5N8-A did not develop any clinical signs, H5N8-B-inoculated and cohoused ducks died after showing neurological signs. Swapping of the HA gene segments did not increase virulence of H5N8-A but abolished virulence and reduced systemic replication of H5N8-B. Only H5N8-A carrying H5N8-B HA, NP, and NS with or without NA exhibited high virulence in inoculated and contact ducks, similar to H5N8-B. Compared to H5N8-A, HA, NA, NS, and NP proteins of H5N8-B possess peculiar differences, which conferred increased receptor binding affinity, neuraminidase activity, efficiency to inhibit interferon-alpha induction, and replication in vitro, respectively. Taken together, this comprehensive study showed that HA is not the only virulence determinant of the panzootic H5N8-B in Pekin ducks, but NP, NS, and to a lesser extent NA were also necessary for the exhibition of high virulence in vivo. These proteins acted synergistically to increase receptor binding affinity, sialidase activity, interferon antagonism, and replication. This is the first ad-hoc study to investigate the mechanism underlying the high virulence of HPAIV in Pekin ducks. IMPORTANCE Since 2014, several waves of avian influenza virus (AIV) H5N8 of clade 2.3.4.4 occurred globally on unprecedented levels. Unlike viruses in the first wave in 2014-2015 (H5N8-A), viruses in 2015-2016 (H5N8-B) exhibited unusually high pathogenicity (HP) in wild and domestic ducks. Here, we found that the high virulence of H5N8-B in Pekin ducks could be attributed to multiple factors in combination, namely, hemagglutinin (HA), neuraminidase (NA), nucleoprotein (NP), and nonstructural protein 1 (NS1). Compared to H5N8-A, H5N8-B possesses distinct genetic and biological properties including increased HA receptor-binding affinity and neuraminidase activity. Likewise, H5N8-B NS1 and NP were more efficient to inhibit interferon induction and enhance replication in primary duck cells, respectively. These results indicate the polygenic trait of virulence of HPAIV in domestic ducks and the altered biological properties of the HPAIV H5N8 clade 2.3.4.4B. These findings may explain the unusual high mortality in Pekin ducks during the panzootic H5N8 outbreaks.

Pathogenicity of highly pathogenic avian influenza H5N8 subtype for herring gulls (Larus argentatus): impact of homo- and heterosubtypic immunity on the outcome of infection

To improve understanding of the pathobiology of highly pathogenic avian influenza virus (HPAIV) infections in wild birds, pathogenicity and transmissibility of HPAIV H5N8 subtype clade 2.3.4.4b was evaluated in ~ 8-week-old herring gulls (Larus argentatus) divided into 3 groups: naïve birds (group A), birds previously exposed to low pathogenic avian influenza virus (LPAIV) H5N1 (group B) and LPAIV H13N6 (group C). The HPAIV H5N8 virus was highly virulent for naïve gulls, that showed early morbidity, high mortality, a broad spectrum of clinical signs, including violent neurological disorders, systemic distribution of the virus in organs accompanied by high level of shedding and transmission to contact birds. Pre-exposure to homologous and heterologous LPAIV subtypes conferred only partial protection: we observed increased survival rate (statistically significant only in group B), nervous signs, pantropic distribution of virus in organs, shedding (significantly reduced in gulls of group C in the early phase of disease and asymptomatic shedding in the late phase), transmission to contact gulls (more pronounced in group B) and near-complete seroconversion in survivors. Histopathological and immunohistochemical results indicate virus tropism for the neural, respiratory and myocardial tissues. In conclusion, we demonstrate that HPAIV H5N8 clade 2.3.4.4b is highly virulent and lethal for fully susceptible herring gulls and that pre-exposure to homo- and heterosubtypic LPAIV only partially modulates the disease outcome.

Tissue Specific Transcriptome Changes Upon Influenza A Virus Replication in the Duck

Ducks are the natural host and reservoir of influenza A virus (IAV), and as such are permissive to viral replication while being unharmed by most strains. It is not known which mechanisms of viral control are globally regulated during infection, and which are specific to tissues during infection. Here we compare transcript expression from tissues from Pekin ducks infected with a recombinant H5N1 strain A/Vietnam 1203/04 (VN1203) or an H5N2 strain A/British Columbia 500/05 using RNA-sequencing analysis and aligning reads to the NCBI assembly ZJU1.0 of the domestic duck (Anas platyrhynchos) genome. Highly pathogenic VN1203 replicated in lungs and showed systemic dissemination, while BC500, like most low pathogenic strains, replicated in the intestines. VN1203 infection induced robust differential expression of genes all three days post infection, while BC500 induced the greatest number of differentially expressed genes on day 2 post infection. While there were many genes globally upregulated in response to either VN1203 or BC500, tissue specific gene expression differences were observed. Lungs of ducks infected with VN1203 and intestines of birds infected with BC500, tissues important in influenza replication, showed highest upregulation of pattern recognition receptors and interferon stimulated genes early in the response. These tissues also appear to have specific downregulation of inflammatory components, with downregulation of distinct sets of proinflammatory cytokines in lung, and downregulation of key components of leukocyte recruitment and complement pathways in intestine. Our results suggest that global and tissue specific regulation patterns help the duck control viral replication as well as limit some inflammatory responses in tissues involved in replication to avoid damage.

Primary Chicken and Duck Endothelial Cells Display a Differential Response to Infection with Highly Pathogenic Avian Influenza Virus

Highly pathogenic avian influenza viruses (HPAIVs) in gallinaceous poultry are associated with viral infection of the endothelium, the induction of a ‘cytokine storm, and severe disease. In contrast, in Pekin ducks, HPAIVs are rarely endothelial tropic, and a cytokine storm is not observed. To date, understanding these species-dependent differences in pathogenesis has been hampered by the absence of a pure culture of duck and chicken endothelial cells. Here, we use our recently established in vitro cultures of duck and chicken aortic endothelial cells to investigate species-dependent differences in the response of endothelial cells to HPAIV H5N1 infection. We demonstrate that chicken and duck endothelial cells display a different transcriptional response to HPAI H5N1 infection in vitro—with chickens displaying a more pro-inflammatory response to infection. As similar observations were recorded following in vitro stimulation with the viral mimetic polyI:C, these findings were not specific to an HPAIV H5N1 infection. However, similar species-dependent differences in the transcriptional response to polyI:C were not observed in avian fibroblasts. Taken together, these data demonstrate that chicken and duck endothelial cells display a different response to HPAIV H5N1 infection, and this may help account for the species-dependent differences observed in inflammation in vivo.

A Semiquantitative Scoring System for Histopathological and Immunohistochemical Assessment of Lesions and Tissue Tropism in Avian Influenza

The main findings of the post-mortem examination of poultry infected with highly pathogenic avian influenza viruses (HPAIV) include necrotizing inflammation and viral antigen in multiple organs. The lesion profile displays marked variability, depending on viral subtype, strain, and host species. Therefore, in this study, a semiquantitative scoring system was developed to compare histopathological findings across a wide range of study conditions. Briefly, the severity of necrotizing lesions in brain, heart, lung, liver, kidney, pancreas, and/or lymphocytic depletion in the spleen is scored on an ordinal four-step scale (0 = unchanged, 1 = mild, 2 = moderate, 3 = severe), and the distribution of the viral antigen in parenchymal and endothelial cells is evaluated on a four-step scale (0 = none, 1 = focal, 2 = multifocal, 3 = diffuse). These scores are used for a meta-analysis of experimental infections with H7N7 and H5N8 (clade 2.3.4.4b) HPAIV in chickens, turkeys, and ducks. The meta-analysis highlights the rather unique endotheliotropism of these HPAIV in chickens and a more severe necrotizing encephalitis in H7N7-HPAIV-infected turkeys. In conclusion, the proposed scoring system can be used to condensate HPAIV-typical pathohistological findings into semiquantitative data, thus enabling systematic phenotyping of virus strains and their tissue tropism.

Recombinant hemagglutinin glycoproteins provide insight into binding to host cells by H5 influenza viruses in wild and domestic birds

Clade 2.3.4.4, H5 subtype highly pathogenic avian influenza viruses (HPAIVs) have caused devastating effects across wild and domestic bird populations. We investigated differences in the intensity and distribution of the hemagglutinin (HA) glycoprotein binding of a clade 2.3.4.4 H5 HPAIV compared to a H5 low pathogenic avian influenza virus (LPAIV). Recombinant HA from gene sequences from a HPAIV, A/Northern pintail/Washington/40964/2014(H5N2) and a LPAIV, A/mallard/MN/410/2000(H5N2) were generated and, via protein histochemistry, HA binding in respiratory, intestinal and cloacal bursal tissue was quantified as median area of binding (MAB). Poultry species, shorebirds, ducks and terrestrial birds were used. Differences in MAB were observed between the HPAIV and LPAIV H5 HAs. We demonstrate that clade 2.3.4.4 HPAIV H5 HA has a broader host cell binding across a variety of bird species compared to the LPAIV H5 HA. These findings support published results from experimental trials, and outcomes of natural disease outbreaks with these viruses.

Pattern Recognition Receptor Signaling and Innate Responses to Influenza A Viruses in the Mallard Duck, Compared to Humans and Chickens

Mallard ducks are a natural host and reservoir of avian Influenza A viruses. While most influenza strains can replicate in mallards, the virus typically does not cause substantial disease in this host. Mallards are often resistant to disease caused by highly pathogenic avian influenza viruses, while the same strains can cause severe infection in humans, chickens, and even other species of ducks, resulting in systemic spread of the virus and even death. The differences in influenza detection and antiviral effectors responsible for limiting damage in the mallards are largely unknown. Domestic mallards have an early and robust innate response to infection that seems to limit replication and clear highly pathogenic strains. The regulation and timing of the response to influenza also seems to circumvent damage done by a prolonged or dysregulated immune response. Rapid initiation of innate immune responses depends on viral recognition by pattern recognition receptors (PRRs) expressed in tissues where the virus replicates. RIG-like receptors (RLRs), Toll-like receptors (TLRs), and Nod-like receptors (NLRs) are all important influenza sensors in mammals during infection. Ducks utilize many of the same PRRs to detect influenza, namely RIG-I, TLR7, and TLR3 and their downstream adaptors. Ducks also express many of the same signal transduction proteins including TBK1, TRIF, and TRAF3. Some antiviral effectors expressed downstream of these signaling pathways inhibit influenza replication in ducks. In this review, we summarize the recent advances in our understanding of influenza recognition and response through duck PRRs and their adaptors. We compare basal tissue expression and regulation of these signaling components in birds, to better understand what contributes to influenza resistance in the duck.

Innate Immune Responses to Avian Influenza Viruses in Ducks and Chickens

Mallard ducks are important natural hosts of low pathogenic avian influenza (LPAI) viruses and many strains circulate in this reservoir and cause little harm. Some strains can be transmitted to other hosts, including chickens, and cause respiratory and systemic disease. Rarely, these highly pathogenic avian influenza (HPAI) viruses cause disease in mallards, while chickens are highly susceptible. The long co-evolution of mallard ducks with influenza viruses has undoubtedly fine-tuned many immunological host–pathogen interactions to confer resistance to disease, which are poorly understood. Here, we compare innate responses to different avian influenza viruses in ducks and chickens to reveal differences that point to potential mechanisms of disease resistance. Mallard ducks are permissive to LPAI replication in their intestinal tissues without overtly compromising their fitness. In contrast, the mallard response to HPAI infection reflects an immediate and robust induction of type I interferon and antiviral interferon stimulated genes, highlighting the importance of the RIG-I pathway. Ducks also appear to limit the duration of the response, particularly of pro-inflammatory cytokine expression. Chickens lack RIG-I, and some modulators of the signaling pathway and may be compromised in initiating an early interferon response, allowing more viral replication and consequent damage. We review current knowledge about innate response mediators to influenza infection in mallard ducks compared to chickens to gain insight into protective immune responses, and open questions for future research.

Polymorphism of duck MHC class molecules

Major histocompatibility complex class I (MHC I) molecules are critically involved in defense against pathogens, and their high polymorphism is advantageous to a range of immune responses, especially in duck displaying biased expression of one MHC I gene. Here, we examined MHC I polymorphism in two duck (Anas platyrhynchos) breeds from China: Shaoxing (SX) and Jinding (JD). Twenty-seven unique UAA alleles identified from the MHC I genes of these breeds were analyzed concerning amino acid composition, homology, and phylogenetic relationships. Based on amino acid sequence homology, allelic groups of Anas platyrhynchos MHC I (Anpl-MHC I) were established and their distribution was analyzed. Then, highly variable sites (HVSs) in peptide-binding domains (PBD) were estimated and located in the three-dimensional structure of Anpl-MHC I. The UAA alleles identified showed high polymorphism, based on full-length sequence homology. By adding the alleles found here to known Anpl-MHC I genes from domestic ducks, they could be divided into 17 groups and four novel groups were revealed for SX and JD ducks. The UAA alleles of the two breeds were not divergent from the MHC I of other duck breeds, and HVSs were mostly located in the peptide-binding groove (PBG), suggesting that they might determine peptide-binding characteristics and subsequently influence peptide presentation and recognition. The results from the present study enrich Anpl-MHC I polymorphism data and clarify the distribution of alleles with different peptide-binding specificities, which might also accelerate effective vaccine development and help control various infections in ducks.

The Drivers of Pathology in Zoonotic Avian Influenza: The Interplay Between Host and Pathogen

The emergence of zoonotic strains of avian influenza (AI) that cause high rates of mortality in people has caused significant global concern, with a looming threat that one of these strains may develop sustained human-to-human transmission and cause a pandemic outbreak. Most notable of these viral strains are the H5N1 highly pathogenic AI and the H7N9 low pathogenicity AI viruses, both of which have mortality rates above 30%. Understanding of their mechanisms of infection and pathobiology is key to our preparation for these and future viral strains of high consequence. AI viruses typically circulate in wild bird populations, commonly infecting waterfowl and also regularly entering commercial poultry flocks. Live poultry markets provide an ideal environment for the spread AI and potentially the selection of mutants with a greater propensity for infecting humans because of the potential for spill over from birds to humans. Pathology from these AI virus infections is associated with a dysregulated immune response, which is characterized by systemic spread of the virus, lymphopenia, and hypercytokinemia. It has been well documented that host/pathogen interactions, particularly molecules of the immune system, play a significant role in both disease susceptibility as well as disease outcome. Here, we review the immune/virus interactions in both avian and mammalian species, and provide an overview or our understanding of how immune dysregulation is driven. Understanding these susceptibility factors is critical for the development of new vaccines and therapeutics to combat the next pandemic influenza.

Co-infection of highly pathogenic avian influenza and duck hepatitis viruses in Egyptian backyard and commercial ducks

Highly pathogenic avian influenza (HPAI) H5N1 virus poses a major challenge to the poultry industry and human health in Egypt. Twenty one households and eight duck farms in Sharkia Province, Egypt were investigated for the presence of avian influenza virus (AIV) and/or duck hepatitis virus 1 (DHV-1). Mortality rates among the investigated farms and yards were, 18.9% (69/365) of native ducks, 60.9% (25/41) of Pekin ducks, 60.2% (6306/10473) of Muscovy ducks and 44.9% (1353/3015) of Mallard ducks. The RT-PCR revealed the circulation of HPAI-H5N1 virus (81/104) among the examined birds with a high percentage in Muscovy (83.7%) and Pekin (83.4%) ducks. Interestingly, co-infection of HPAI and DHV-1 viruses in three ducklings with age of 4–19 days was detected. Severe neurological signs with high mortality were observed in ducklings as early as 4 days of age. Influenza virus antigen was detected in the neurons and glial cells of the brain, hepatocytes, and the intestinal submucosal plexus. Although, genetic characterization of H5N1 isolates revealed HPAIV of clade 2.2.1.2, such increased mortalities and neurological signs regardless of the duck age might imply the natural selection of HPAI in ducks. Crucial monitoring of the disease situation in ducks is essential for the implementation of an effective prevention and control program.

Study of an Outbreak of Highly Pathogenic Avian Influenza H5N8 in Commercial Pekin Ducks ( Anas platyrhynchos domesticus) in California

A February 2015 outbreak of highly pathogenic avian influenza (HPAI) H5N8 in a flock of commercial Pekin ducks ( Anas platyrhynchos domesticus) in California was investigated in detail. Approximately 17,349 five-wk-old ducks experienced an increased mortality from a normal of eight birds per day to 24, 18, 24, 33, and 61 birds per day, respectively, in the last 5 days prior to flock depopulation. Clinically, there was decreased water and feed consumption, and approximately 1.0% of the affected flock exhibited neurologic signs. Necropsy of five clinically ill ducks revealed pale, patchy areas on the epicardium in two birds, pale foci of necrosis in the liver of one bird, and airsacculitis in three birds. Histopathology revealed multifocal nonsuppurative encephalomyelitis, myocarditis, myositis, pancreatitis, hepatitis, and glossitis. Immunohistochemistry revealed avian influenza virus (AIV) nucleoprotein in the nucleus and cytoplasm of various cells in the aforementioned organs, as well as in the skin and feathers. Eight of the 10 sera samples tested were positive for avian influenza antibodies by agar gel immunodiffusion serology. Oropharyngeal and cloacal swabs taken from 15 birds, as well as from the lungs, livers, pancreas, and spleen, were positive for AIV by real-time reverse transcriptase (rRT) PCR. AIV was isolated and typed as Eurasian lineage HPAI H5N8, clade 2.3.4.4, by the National Veterinary Services Laboratory, Ames, IA. Extensive surveillance of birds for AIV around the 10-km zone did not reveal any additional cases. Ducks on the affected premises were humanely euthanatized by foam and composted in-house, the houses were heated to 57 C for 4 days, and swabs were taken periodically from the compost to ensure negativity for AIV by rRT-PCR. The compost and litter were then removed, and the house was pressure cleaned, disinfected, and repopulated approximately 120 days after euthanatization of the ducks.

Structural Definition of Duck Major Histocompatibility Complex Class I Molecules That Might Explain Efficient Cytotoxic T Lymphocyte Immunity to Influenza A Virus

A single dominantly expressed allele of major histocompatibility complex class I (MHC I) may be responsible for the duck's high tolerance to highly pathogenic influenza A virus (HP-IAV) compared to the chicken's lower tolerance. In this study, the crystal structures of duck MHC I (Anpl-UAA*01) and duck β2-microglobulin (β2m) with two peptides from the H5N1 strains were determined. Two remarkable features were found to distinguish the Anpl-UAA*01 complex from other known MHC I structures. A disulfide bond formed by Cys⁹⁵ and Cys¹¹² and connecting the β5 and β6 sheets at the bottom of peptide binding groove (PBG) in Anpl-UAA*01 complex, which can enhance IAV peptide binding, was identified. Moreover, the interface area between duck MHC I and β2m was found to be larger than in other species. In addition, the two IAV peptides that display distinctive conformations in the PBG, B, and F pockets act as the primary anchor sites. Thirty-one IAV peptides were used to verify the peptide binding motif of Anpl-UAA*01, and the results confirmed that the peptide binding motif is similar to that of HLA-A*0201. Based on this motif, approximately 600 peptides from the IAV strains were partially verified as the candidate epitope peptides for Anpl-UAA*01, which is a far greater number than those for chicken BF2*2101 and BF2*0401 molecules. Extensive IAV peptide binding should allow for ducks with this Anpl-UAA*01 haplotype to resist IAV infection.

IMPORTANCE Ducks are natural reservoirs of influenza A virus (IAV) and are more resistant to the IAV than chickens. Both ducks and chickens express only one dominant MHC I locus providing resistance to the virus. To investigate how MHC I provides IAV resistance, crystal structures of the dominantly expressed duck MHC class I (pAnpl-UAA*01) with two IAV peptides were determined. A disulfide bond was identified in the peptide binding groove that can facilitate Anpl-UAA*01 binding to IAV peptides. Anpl-UAA*01 has a much wider recognition spectrum of IAV epitope peptides than do chickens. The IAV peptides bound by Anpl-UAA*01 display distinctive conformations that can help induce an extensive cytotoxic T lymphocyte (CTL) response. In addition, the interface area between the duck MHC I and β2m is larger than in other species. These results indicate that HP-IAV resistance in ducks is due to extensive CTL responses induced by MHC I.

Infectivity, transmission and pathogenicity of H5 highly pathogenic avian influenza clade 2.3.4.4 (H5N8 and H5N2) United States index viruses in Pekin ducks and Chinese geese

In late 2014, a H5N8 highly pathogenic avian influenza (HPAI) virus, clade 2.3.4.4, spread by migratory waterfowl into North America reassorting with low pathogenicity AI viruses to produce a H5N2 HPAI virus. Since domestic waterfowl are common backyard poultry frequently in contact with wild waterfowl, the infectivity, transmissibility, and pathogenicity of the United States H5 HPAI index viruses (H5N8 and H5N2) was investigated in domestic ducks and geese. Ducks infected with the viruses had an increase in body temperature but no or mild clinical signs. Infected geese did not show increase in body temperature and most only had mild clinical signs; however, some geese presented severe neurological signs. Ducks became infected and transmitted the viruses to contacts when inoculated with high virus doses [(104 and 106 50% embryo infective dose (EID50)], but not with a lower dose (102 EID50). Geese inoculated with the H5N8 virus became infected regardless of the virus dose given, and transmitted the virus to direct contacts. Only geese inoculated with the higher doses of the H5N2 and their contacts became infected, indicating differences in infectivity between the two viruses and the two waterfowl species. Geese shed higher titers of virus and for a longer period of time than ducks. In conclusion, the H5 HPAI viruses can infect domestic waterfowl and easily transmit to contact birds, with geese being more susceptible to infection and disease than ducks. The disease is mostly asymptomatic, but infected birds shed virus for several days representing a risk to other poultry species.

Pathogenicity and Transmission of H5 and H7 Highly Pathogenic Avian Influenza Viruses in Mallards

Wild aquatic birds have been associated with the intercontinental spread of H5 subtype highly pathogenic avian influenza (HPAI) viruses of the A/goose/Guangdong/1/96 (Gs/GD) lineage during 2005, 2010, and 2014, but dispersion by wild waterfowl has not been implicated with spread of other HPAI viruses. To better understand why Gs/GD H5 HPAI viruses infect and transmit more efficiently in waterfowl than other HPAI viruses, groups of mallard ducks were challenged with one of 14 different H5 and H7 HPAI viruses, including a Gs/GD lineage H5N1 (clade 2.2) virus from Mongolia, part of the 2005 dispersion, and the H5N8 and H5N2 index HPAI viruses (clade 2.3.4.4) from the United States, part of the 2014 dispersion. All virus-inoculated ducks and contact exposed ducks became infected and shed moderate to high titers of the viruses, with the exception that mallards were resistant to Ck/Pennsylvania/83 and Ck/Queretaro/95 H5N2 HPAI virus infection. Clinical signs were only observed in ducks challenged with the H5N1 2005 virus, which all died, and with the H5N8 and H5N2 2014 viruses, which had decreased weight gain and fever. These three viruses were also shed in higher titers by the ducks, which could facilitate virus transmission and spread. This study highlights the possible role of wild waterfowl in the spread of HPAI viruses.

IMPORTANCE

The spread of H5 subtype highly pathogenic avian influenza (HPAI) viruses of the Gs/GD lineage by migratory waterfowl is a serious concern for animal and public health. H5 and H7 HPAI viruses are considered to be adapted to gallinaceous species (chickens, turkeys, quail, etc.) and less likely to infect and transmit in wild ducks. In order to understand why this is different with certain Gs/GD lineage H5 HPAI viruses, we compared the pathogenicity and transmission of several H5 and H7 HPAI viruses from previous poultry outbreaks to Gs/GD lineage H5 viruses, including H5N1 (clade 2.2), H5N8 and H5N2 (clade 2.3.4.4) viruses, in mallards as a representative wild duck species. Surprisingly, most HPAI viruses examined in this study replicated well and transmitted among mallards; however, the three Gs/GD lineage H5 HPAI viruses replicated to higher titers, which could explain the transmission of these viruses in susceptible wild duck populations.

Highly Pathogenic Avian Influenza (H5N1) Virus in Feathers

H5N1 highly pathogenic avian influenza (HPAI) virus causes high mortality of infected birds, with infection in multiple organs, including in feathers. Feathers have been proposed as samples for diagnosis of HPAI infection in birds, and this study is part of a broader investigation validating the use of feathers for diagnostic purposes. To understand and characterize the morphological basis for feather infection, sections from 7 different skin tracts of ducks and chickens infected with 3 different clades of H5N1 HPAI virus from Indonesia and Vietnam were examined histologically. Results showed that in ducks, lesions and viral antigen were mainly detected in the epidermis of feathers and follicles, whereas in chickens, they were mostly found in the dermis of these structures. Abundant viral antigen was found in nearly all the feathers examined from chickens, and there was no apparent difference between virus isolates or skin tracts in the proportion of feathers that were antigen positive. By immunohistochemistry, the majority of feathers from most skin tracts from ducks infected with a Vietnamese H5N1 HPAI virus contained abundant levels of viral antigen, while few feathers were antigen positive from ducks infected with 2 Indonesian viruses. These results support and inform the use of feathers for diagnostic detection of H5N1 HPAI virus in birds.

Molecular pathogenesis of H5 highly pathogenic avian influenza: the role of the haemagglutinin cleavage site motif

The emergence of H5N1 highly pathogenic avian influenza has caused a heavy socio‐economic burden through culling of poultry to minimise human and livestock infection. Although human infections with H5N1 have to date been limited, concerns for the pandemic potential of this zoonotic virus have been greatly intensified following experimental evidence of aerosol transmission of H5N1 viruses in a mammalian infection model. In this review, we discuss the dominance of the haemagglutinin cleavage site motif as a pathogenicity determinant, the host‐pathogen molecular interactions driving cleavage activation, reverse genetics manipulations and identification of residues key to haemagglutinin cleavage site functionality and the mechanisms of cell and tissue damage during H5N1 infection. We specifically focus on the disease in chickens, as it is in this species that high pathogenicity frequently evolves and from which transmission to the human population occurs. With >75% of emerging infectious diseases being of zoonotic origin, it is necessary to understand pathogenesis in the primary host to explain spillover events into the human population. © 2015 The Authors. Reviews in Medical Virology published by John Wiley & Sons Ltd.

A comparative evaluation of feathers, oropharyngeal swabs, and cloacal swabs for the detection of H5N1 highly pathogenic avian influenza virus infection in experimentally infected chickens and ducks

Oropharyngeal and cloacal swabs have been widely used for the detection of H5N1 highly pathogenic avian Influenza A virus (HPAI virus) in birds. Previous studies have shown that the feather calamus is a site of H5N1 virus replication and therefore has potential for diagnosis of avian influenza. However, studies characterizing the value of feathers for this purpose are not available, to our knowledge; herein we present a study investigating feathers for detection of H5N1 virus. Ducks and chickens were experimentally infected with H5N1 HPAI virus belonging to 1 of 3 clades (Indonesian clades 2.1.1 and 2.1.3, Vietnamese clade 1). Different types of feathers and oropharyngeal and cloacal swab samples were compared by virus isolation. In chickens, virus was detected from all sample types: oral and cloacal swabs, and immature pectorosternal, flight, and tail feathers. During clinical disease, the viral titers were higher in feathers than swabs. In ducks, the proportion of virus-positive samples was variable depending on viral strain and time from challenge; cloacal swabs and mature pectorosternal feathers were clearly inferior to oral swabs and immature pectorosternal, tail, and flight feathers. In ducks infected with Indonesian strains, in which most birds did not develop clinical signs, all sampling methods gave intermittent positive results; 3-23% of immature pectorosternal feathers were positive during the acute infection period; oropharyngeal swabs had slightly higher positivity during early infection, while feathers performed better during late infection. Our results indicate that immature feathers are an alternative sample for the diagnosis of HPAI in chickens and ducks.

Body temperature changes during simulated bacterial infection in a songbird: fever at night and hypothermia during the day

Although fever (a closely regulated increase in body temperature in response to infection) typically is beneficial, it is energetically costly and may induce detrimentally high body temperatures. This can increase the susceptibility to energetic bottlenecks and risks of overheating in some organisms. Accordingly, it could be particularly interesting to study fever in small birds, which have comparatively high metabolic rates and high, variable body temperatures. We therefore investigated two aspects of fever and other sickness behaviours (circadian variation, dose dependence) in a small songbird, the zebra finch. We injected lipopolysaccharide (LPS) at the beginning of either the day or the night, and subsequently monitored body temperature, body mass change and food intake for the duration of the response. We found pronounced circadian variation in the body temperature response to LPS injection, manifested by (dose-dependent) hypothermia during the day but fever at night. This resulted in body temperature during the peak response being relatively similar during the day and night. Day-to-night differences might be explained in the context of circadian variation in body temperature: songbirds have a high daytime body temperature that is augmented by substantial heat production peaks during activity. This might require a trade-off between the benefit of fever and the risk of overheating. In contrast, at night, when body temperature is typically lower and less variable, fever can be used to mitigate infection. We suggest that the change in body temperature during infection in small songbirds is context dependent and regulated to promote survival according to individual demands at the time of infection.

Veterinary influenza vaccines against avian influenza in China

ABSTRACT 

Avian influenza (AI) is an infectious viral illness that affects numerous species of birds, including chickens, ducks, turkeys and geese. Poultry vaccination plays an important role for control of the AI virus and effectively prevents the infection in domestic chickens. However, new, increasingly virulent strains are constantly emerging, for which no vaccines are available. Avian influenza is also responsible for sporadically infecting humans and causing a wide range of clinical outcomes. Here, we review the recent emergence of diverse strains of the AI virus and the use of veterinary vaccines for poultry in China.

Analysis of signs and pathology of H5N1-infected ducks from the 2010-2011 Korean highly pathogenic avian influenza outbreak suggests the influence of age and management practices on severity of disease

We compared the clinical signs, histopathological lesions and distribution of viral antigens among infected young (meat-type) and older (breeder) ducks that were naturally infected with the highly pathogenic avian influenza (HPAI) virus during the 2010-2011 Korean outbreak. The meat-type ducks had a high mortality rate (30%) and showed severe neurological signs such as head tremors and paresis. In contrast, HPAI-infected breeder ducks had minimal clinical signs but a decreased egg production rate. The histopathological characteristics of infected meat-type ducks included necrotic lesions of heart and brain, which may have primarily contributed to the high mortality rate. In contrast, the breeder ducks only presented necrotic splenitis, and viral antigens were only detected in the trachea, lungs and spleen. Younger ducks had a high viral titre in the organs, high levels of viral shedding and a high mortality rate after experimental HPAI virus infection. Compared to the breeder ducks, the meat-type ducks were raised in smaller farms that had poor quarantine and breeding facilities. It is therefore possible that better biosecurity in the breeder farms could have reduced the infection dose and subsequently the severity of the disease. Thus, age and management may be the influencing factors for HPAI susceptibility in ducks.

PA-X decreases the pathogenicity of highly pathogenic H5N1 influenza A virus in avian species by inhibiting virus replication and host response

PA-X is a newly discovered protein that decreases the virulence of the 1918 H1N1 virus in a mouse model. However, the role of PA-X in the pathogenesis of highly pathogenic avian influenza viruses (HPAIV) of the H5N1 subtype in avian species is totally unknown. By generating two PA-X-deficient viruses and evaluating their virulence in different animal models, we show here that PA-X diminishes the virulence of the HPAIV H5N1 strain A/Chicken/Jiangsu/k0402/2010 (CK10) in mice, chickens, and ducks. Expression of PA-X dampens polymerase activity and virus replication both in vitro and in vivo. Using microarray analysis, we found that PA-X blunts the global host response in chicken lungs, markedly downregulating genes associated with the inflammatory and cell death responses. Correspondingly, a decreased cytokine response was recapitulated in multiple organs of chickens and ducks infected with the wild-type virus relative to those infected with the PA-X-deficient virus. In addition, the PA-X protein exhibits antiapoptotic activity in chicken and duck embryo fibroblasts. Thus, our results demonstrated that PA-X acts as a negative virulence regulator and decreases virulence by inhibiting viral replication and the host innate immune response. Therefore, we here define the role of PA-X in the pathogenicity of H5N1 HPAIV, furthering our understanding of the intricate pathogenesis of influenza A virus.

IMPORTANCE

Influenza A virus (IAV) continues to pose a huge threat to global public health. Eight gene segments of the IAV genome encode as many as 17 proteins, including 8 main viral proteins and 9 accessory proteins. The presence of these accessory proteins may further complicate the pathogenesis of IAV. PA-X is a newly identified protein in segment 3 that acts to decrease the virulence of the 1918 H1N1 virus in mice by modulating host gene expression. Our study extends these functions of PA-X to H5N1 HPAIV. We demonstrated that loss of PA-X expression increases the virulence and replication of an H5N1 virus in mice and avian species and alters the host innate immune and cell death responses. Our report is the first to delineate the role of the novel PA-X protein in the pathogenesis of H5N1 viruses in avian species and promotes our understanding of H5N1 HPAIV.

Crucial role of PA in virus life cycle and host adaptation of influenza A virus

The PA protein is the third subunit of the polymerase complex of influenza A virus. Compared with the other two polymerase subunits (PB2 and PB1), its precise functions are less defined. However, in recent years, advances in protein expression and crystallization technologies and also the reverse genetics, greatly accelerate our understanding of the essential role of PA in virus infection. Here, we first review the current literature on this remarkably multifunctional viral protein regarding virus life cycle, including viral RNA transcription and replication, viral genome packaging and assembly. We then discuss the various roles of PA in host adaption in avian species and mammals, general virus-host interaction, and host protein synthesis shutoff. We also review the recent findings about the novel proteins derived from PA. Finally, we discuss the prospects of PA as a target for the development of new antiviral approaches and drugs.

H5N1 infection causes rapid mortality and high cytokine levels in chickens compared to ducks

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Chickens are acutely susceptible to influenza when compared with ducks.

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The chicken innate immune responses to influenza are more pronounced than ducks.

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IL6 is rapidly upregulated in chickens compared to ducks.

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Cytokine profile, especially IL6, may lead to acute pathogenicity in chickens.

Infection with H5N1 influenza virus is often fatal to poultry with death occurring in hours rather than days. However, whilst chickens may be acutely susceptible, ducks appear to be asymptomatic to H5N1. The mechanisms of disease pathogenesis are not well understood and the variation between different species requires investigation to help explain these species differences. Here we investigated the expression of several key proinflammatory cytokines of chickens and ducks following infection with 2 highly pathogenic H5N1 (A/Muscovy duck/Vietnam/453/2004 (Vt453) and A/Duck/Indramayu/BBVW/109/2006 (Ind109)) and a low-pathogenic H5N3 influenza virus (A/Duck/Victoria/1462/2008 (Vc1462)). H5N1 viruses caused fatal infections in chickens as well as high viral loads and increased production of proinflammatory molecules when compared to ducks. Cytokines, including Interleukin 6 (IL6) and the acute phase protein Serum Amyloid A (SAA), were rapidly induced at 24 h post infection with H5N1. In contrast, low induction of these cytokines appeared in ducks and only at later times during the infection period. These observations support that hypercytokinemia may contribute to pathogenesis in chickens, whilst the lower cytokine response in ducks may be a factor in their apparent resistance to disease and decreased mortality.

Experimentally infected domestic ducks show efficient transmission of Indonesian H5N1 highly pathogenic avian influenza virus, but lack persistent viral shedding

Ducks are important maintenance hosts for avian influenza, including H5N1 highly pathogenic avian influenza viruses. A previous study indicated that persistence of H5N1 viruses in ducks after the development of humoral immunity may drive viral evolution following immune selection. As H5N1 HPAI is endemic in Indonesia, this mechanism may be important in understanding H5N1 evolution in that region. To determine the capability of domestic ducks to maintain prolonged shedding of Indonesian clade 2.1 H5N1 virus, two groups of Pekin ducks were inoculated through the eyes, nostrils and oropharynx and viral shedding and transmission investigated. Inoculated ducks (n = 15), which were mostly asymptomatic, shed infectious virus from the oral route from 1 to 8 days post inoculation, and from the cloacal route from 2–8 dpi. Viral ribonucleic acid was detected from 1–15 days post inoculation from the oral route and 1–24 days post inoculation from the cloacal route (cycle threshold <40). Most ducks seroconverted in a range of serological tests by 15 days post inoculation. Virus was efficiently transmitted during acute infection (5 inoculation-infected to all 5 contact ducks). However, no evidence for transmission, as determined by seroconversion and viral shedding, was found between an inoculation-infected group (n = 10) and contact ducks (n = 9) when the two groups only had contact after 10 days post inoculation. Clinical disease was more frequent and more severe in contact-infected (2 of 5) than inoculation-infected ducks (1 of 15). We conclude that Indonesian clade 2.1 H5N1 highly pathogenic avian influenza virus does not persist in individual ducks after acute infection.

Natural history of highly pathogenic avian influenza H5N1

The ecology of highly pathogenic avian influenza (HPAI) H5N1 has significantly changed from sporadic outbreaks in terrestrial poultry to persistent circulation in terrestrial and aquatic poultry and potentially in wild waterfowl. A novel genotype of HPAI H5N1 arose in 1996 in Southern China and through ongoing mutation, reassortment, and natural selection, has diverged into distinct lineages and expanded into multiple reservoir hosts. The evolution of Goose/Guangdong-lineage highly pathogenic H5N1 viruses is ongoing: while stable interactions exist with some reservoir hosts, these viruses are continuing to evolve and adapt to others, and pose an un-calculable risk to sporadic hosts, including humans.

Suboptimal protection against H5N1 highly pathogenic avian influenza viruses from Vietnam in ducks vaccinated with commercial poultry vaccines

Domestic ducks are the second most abundant poultry species in many Asian countries including Vietnam, and play a critical role in the epizootiology of H5N1 highly pathogenic avian influenza (HPAI) [FAO]. In this study, we examined the protective efficacy in ducks of two commercial H5N1 vaccines widely used in Vietnam; Re-1 containing A/goose/Guangdong/1/1996 hemagglutinin (HA) clade 0 antigens, and Re-5 containing A/duck/Anhui/1/2006 HA clade 2.3.4 antigens. Ducks received two doses of either vaccine at 7 and at 14 or 21 days of age followed by challenge at 30 days of age with viruses belonging to the HA clades 1.1, 2.3.4.3, 2.3.2.1.A and 2.3.2.1.B isolated between 2008 and 2011 in Vietnam. Ducks vaccinated with the Re-1 vaccine were protected after infection with the two H5N1 HPAI viruses isolated in 2008 (HA clades 1.1 and 2.3.4.3) showing no mortality and limited virus shedding. The Re-1 and Re-5 vaccines conferred 90-100% protection against mortality after challenge with the 2010 H5N1 HPAI viruses (HA clade 2.3.2.1.A); but vaccinated ducks shed virus for more than 7 days after challenge. Similarly, the Re-1 and Re-5 vaccines only showed partial protection against the 2011 H5N1 HPAI viruses (HA clade 2.3.2.1.A and 2.3.2.1.B), with a high proportion of vaccinated ducks shedding virus for more than 10 days. Furthermore, 50% mortality was observed in ducks vaccinated with Re-1 and challenged with the 2.3.2.1.B virus. The HA proteins of the 2011 challenge viruses had the greatest number of amino acid differences from the two vaccines as compared to the viruses from 2008 and 2009, which correlates with the lesser protection observed with these viruses. These studies demonstrate the suboptimal protection conferred by the Re-1 and Re-5 commercial vaccines in ducks against H5N1 HPAI clade 2.3.2.1 viruses, and underscore the importance of monitoring vaccine efficacy in the control of H5N1 HPAI in ducks.

The PA and HA gene-mediated high viral load and intense innate immune response in the brain contribute to the high pathogenicity of H5N1 avian influenza virus in mallard ducks

Most highly pathogenic avian influenza A viruses cause only mild clinical signs in ducks, serving as an important natural reservoir of influenza A viruses. However, we isolated two H5N1 viruses that are genetically similar but differ greatly in virulence in ducks. A/Chicken/Jiangsu/k0402/2010 (CK10) is highly pathogenic, whereas A/Goose/Jiangsu/k0403/2010 (GS10) is low pathogenic. To determine the genetic basis for the high virulence of CK10 in ducks, we generated a series of single-gene reassortants between CK10 and GS10 and tested their virulence in ducks. Expression of the CK10 PA or hemagglutinin (HA) gene in the GS10 context resulted in increased virulence and virus replication. Conversely, inclusion of the GS10 PA or HA gene in the CK10 background attenuated the virulence and virus replication. Moreover, the PA gene had a greater contribution. We further determined that residues 101G and 237E in the PA gene contribute to the high virulence of CK10. Mutations at these two positions produced changes in virulence, virus replication, and polymerase activity of CK10 or GS10. Position 237 plays a greater role in determining these phenotypes. Moreover, the K237E mutation in the GS10 PA gene increased PA nuclear accumulation. Mutant GS10 viruses carrying the CK10 HA gene or the PA101G or PA237E mutation induced an enhanced innate immune response. A sustained innate response was detected in the brain rather than in the lung and spleen. Our results suggest that the PA and HA gene-mediated high virus replication and the intense innate immune response in the brain contribute to the high virulence of H5N1 virus in ducks.

Effect of species, breed and route of virus inoculation on the pathogenicity of H5N1 highly pathogenic influenza (HPAI) viruses in domestic ducks

H5N1 highly pathogenic avian influenza (HPAI) viruses continue to be a threat to poultry in many regions of the world. Domestic ducks have been recognized as one of the primary factors in the spread of H5N1 HPAI. In this study we examined the pathogenicity of H5N1 HPAI viruses in different species and breeds of domestic ducks and the effect of route of virus inoculation on the outcome of infection. We determined that the pathogenicity of H5N1 HPAI viruses varies between the two common farmed duck species, with Muscovy ducks (Cairina moschata) presenting more severe disease than various breeds of Anas platyrhynchos var. domestica ducks including Pekin, Mallard-type, Black Runners, Rouen, and Khaki Campbell ducks. We also found that Pekin and Muscovy ducks inoculated with two H5N1 HPAI viruses of different virulence, given by any one of three routes (intranasal, intracloacal, or intraocular), became infected with the viruses. Regardless of the route of inoculation, the outcome of infection was similar for each species but depended on the virulence of the virus used. Muscovy ducks showed more severe clinical signs and higher mortality than the Pekin ducks. In conclusion, domestic ducks are susceptible to H5N1 HPAI virus infection by different routes of exposure, but the presentation of the disease varied by virus strain and duck species. This information helps support the planning and implementation of H5N1 HPAI surveillance and control measures in countries with large domestic duck populations.

Differences in highly pathogenic avian influenza viral pathogenesis and associated early inflammatory response in chickens and ducks

We studied the immunological responses in the lung, brain and spleen of ducks and chickens within the first 7 days after infection with H7N1 highly pathogenic avian influenza (HPAI). Infection with HPAI caused significant morbidity and mortality in chickens, while in ducks the infection was asymptomatic. The HPAI viral mRNA load was higher in all investigated tissues of chickens compared with duck tissues. In the lung, brain and spleen of HPAI-infected chickens, a high, but delayed, pro-inflammatory response of IL-6 and IL-1β mRNA was induced, including up-regulation of IFN-β, IFN-γ, TLR3 and MDA-5 mRNA from 1 day post infection (p.i.). Whereas in ducks already at 8 h p.i., a quicker but lower response was found for IL-6, IL-1β and iNOS mRNA followed by a delayed activation of TLR7, RIG-I, MDA5 and IFN-γ mRNA response. Virus-infected areas in the lung of chickens co-localized with KUL-01⁺ (macrophages, dendritic cells), CD4⁺, and CD8α⁺ cells, during the first day after infection. However, only KUL-01⁺ cells co-localized with the virus after 1 day p.i. In ducks, CVI-ChNL-68.1⁺ (macrophage-like cells), CD4⁺ and CD8α⁺ cells and apoptosis co-localized with the virus within 8 h p.i. Apoptosis was detected in the brain and lung of HPAI-infected chickens after 2 days p.i. and apoptotic cells co-localized with virus-infected areas. In conclusion, excessive delayed cytokine inflammatory responses but inadequate cellular immune responses may contribute to pathogenesis in chickens, while ducks initiate a fast lower cytokine response followed by the activation of major pattern recognition receptors (TLR7, RIG-I, MDA5) and a persistent cellular response.

The pathobiology of two Indonesian H5N1 avian influenza viruses representing different clade 2.1 sublineages in chickens and ducks

To determine the pathobiology of Indonesian H5N1 highly pathogenic avian influenza, two viruses representing clades 2.1.1 and 2.1.3 were inoculated into broiler chickens and Pekin ducks via the eyes, nostrils and oropharynx. In chickens, both viruses produced fulminant disease; tissue tropism was broad but predominantly endothelial and viral loads in tissues were high. Except for one case of meningoencephalitis, the infection in ducks was sub-clinical, leading only to seroconversion. In these ducks, virus and viral antigen occurred in lower amounts, mainly in the respiratory tract (airsac and sinuses), prior to day 7 after inoculation. During clinical disease, chickens shed high virus titres orally and cloacally. Ducks intermittently shed low virus titres from the oral route for up to 8 days post-inoculation. We discuss the significance of the data for understanding the pathogenesis and pathobiology of Indonesian H5N1 in chickens and ducks.

Multiple routes of invasion of wild-type Clade 1 highly pathogenic avian influenza H5N1 virus into the central nervous system (CNS) after intranasal exposure in ferrets

Human infections with highly pathogenic avian influenza (HPAI) H5N1 have been associated with central nervous system involvement. The purpose of this study was to examine the route of invasion of wild-type HPAI H5N1 virus into the central nervous system (CNS) using a ferret model of infection. Sixteen ferrets were exposed by the intranasal route to 10(6) TCID(50) of A/Vietnam/1203/04, a Clade 1 strain originally isolated from a fatal human case. The ferrets were euthanased for histological and virological analysis at intervals after challenge at 1, 3, 5, 6 and 7 days post-inoculation (dpi). From 5 dpi encephalitis was seen in all examined ferrets. The detection of antigen in the olfactory epithelium, the olfactory bulb, and related nuclei, in that temporal sequence, supported the contention that this is a major infection route for this virus strain. The detection of antigen in the epithelial cells in the Eustachian tube on 1 dpi, followed by the cochlea and vestibulocochlear nerve on 5 dpi is consistent with a second anterograde route of invasion, namely the vestibulocochlear pathway. There was also antigen in the lining of the ventricles and central canal indicating spread via the cerebrospinal fluid. However, evidence for haematogenous dissemination in the form of antigen in the brain parenchyma surrounding blood vessels was not found. This study provides support to the contention that wild-type HPAI H5N1 virus strains may enter the CNS via cranial nerve pathways and that the ferret is an appropriate model to study preventive and therapeutic procedures involving neural infection with these viruses by this route.

Antibody response and viral shedding profile of Egyptian geese (Alopochen aegyptiacus) infected with low pathogenicity H7N1 and H6N8 avian influenza viruses

Egyptian geese (Alopochen aegypticus), a duck species endemic to sub-Saharan Africa and occasionally implicated in the transmission of avian influenza viruses (AIV) to farmed ostriches, were experimentally infected with low pathogenicity H7N1 and H6N8 viruses to assess viral shedding and immune profiles. Following the first infection with H7N1 virus, high titers of virus were shed from both the tracheae and cloacae for at least 7 days postinfection, and tracheal shedding lasting until day 14. All detectable shedding from both tracheae and cloacae had ceased within 28 days of infection. Antibody titers peaked at day 7 postinfection, but the initial immune response was short-lived. Birds that received a second challenge with the homologous H7N1 virus mounted a more robust response that lasted beyond 66 days postchallenge, and H7N1 virus was detected, albeit at much lower levels, until day 28 post secondary infection (psi) in the cloaca and beyond day 28 psi in the trachea. Birds that received an initial infection with H7N1 virus were also challenged with H6N8 virus, and because a comparable shedding pattern to the H7N1 challenge group was observed, we concluded that the effect of any nonspecific immunity was negligible.

Incidence and risk factors for H5 highly pathogenic avian influenza infection in flocks of apparently clinically healthy ducks

A prospective longitudinal study was conducted on 96 smallholder duck farms in Indonesia over a period of 14 months in 2007 and 2008 to monitor bird- and flock-level incidence rates of H5 highly pathogenic avian influenza (HPAI) infection in duck flocks, and to identify risk factors associated with these flocks becoming H5 seropositive. Flocks that scavenged around neighbouring houses within the village were at increased risk of developing H5 antibodies, as were flocks from which carcases of birds that died during the 2 months between visits were consumed by the family. Duck flock confinement overnight on the farm and sudden deaths of birds between visits were associated with lower risk of the flock developing H5 antibodies. Scavenging around neighbouring houses and non-confinement overnight are likely to be causal risk factors for infection. With this study we have provided insights into farm-level risk factors of HPAI virus introduction into duck flocks. Preventive messages based on these risk factors should be included in HPAI awareness programmes.

Role of position 627 of PB2 and the multibasic cleavage site of the hemagglutinin in the virulence of H5N1 avian influenza virus in chickens and ducks

Highly pathogenic H5N1 avian influenza viruses have caused major disease outbreaks in domestic and free-living birds with transmission to humans resulting in 59% mortality amongst 564 cases. The mutation of the amino acid at position 627 of the viral polymerase basic-2 protein (PB2) from glutamic acid (E) in avian isolates to lysine (K) in human isolates is frequently found, but it is not known if this change affects the fitness and pathogenicity of the virus in birds. We show here that horizontal transmission of A/Vietnam/1203/2004 H5N1 (VN/1203) virus in chickens and ducks was not affected by the change of K to E at PB2-627. All chickens died between 21 to 48 hours post infection (pi), while 70% of the ducks survived infection. Virus replication was detected in chickens within 12 hours pi and reached peak titers in spleen, lung and brain between 18 to 24 hours for both viruses. Viral antigen in chickens was predominantly in the endothelium, while in ducks it was present in multiple cell types, including neurons, myocardium, skeletal muscle and connective tissues. Virus replicated to a high titer in chicken thrombocytes and caused upregulation of TLR3 and several cell adhesion molecules, which may explain the rapid virus dissemination and location of viral antigen in endothelium. Virus replication in ducks reached peak values between 2 and 4 days pi in spleen, lung and brain tissues and in contrast to infection in chickens, thrombocytes were not involved. In addition, infection of chickens with low pathogenic VN/1203 caused neuropathology, with E at position PB2-627 causing significantly higher infection rates than K, indicating that it enhances virulence in chickens.

Pathogenesis of highly pathogenic avian influenza A virus (H7N1) infection in chickens inoculated with three different doses

To study the pathogenesis of a H7N1 highly pathogenic avian influenza virus strain, specific pathogen free chickens were inoculated with decreasing concentrations of virus: 10(5.5) median embryo lethal dose (ELD(50)) (G1), 10(3.5) ELD(50) (G2) and 10(1.5) ELD(50) (G3). Disease progression was monitored over a period of 16 days and sequential necropsies and tissue samples were collected for histological and immunohistochemical examination. Viral RNA loads were also quantified in different tissues, blood, oropharyngeal swabs, and cloacal swabs using quantitative real-time reverse transcriptase-polymerase chain reaction (RT-qPCR). Clinical signs of depression, apathy, listlessness, huddling and ruffled feathers were recorded in G1 and a few G2 birds, whilst neurological signs were only observed in chickens inoculated with the highest dose. Gross lesions of haemorrhages were observed in the unfeathered skin of the comb and legs, and skeletal muscle, lung, pancreas and kidneys of birds inoculated with 10(5.5) ELD(50) and 10(3.5) ELD(50) doses. Microscopic lesions and viral antigen were demonstrated in cells of the nasal cavity, lung, heart, skeletal muscle, brain, spinal cord, gastrointestinal tract, pancreas, liver, bone marrow, thymus, bursa of Fabricius, spleen, kidney, adrenal gland and skin. Viral RNA was detected by RT-qPCR in kidney, lung, intestine, and brain samples of G1 and G2 birds. However, in birds infected with the lowest dose, viral RNA was detected only in brain and lung samples in low amounts at 5 and 7 days post infection. Interestingly, viral shedding was observed in oropharyngeal and cloacal swabs with proportionate decrease with the inoculation dose. We conclude that although an adequate infectious dose is critical in reproducing the clinical infection, chickens exposed to lower doses can be infected and shed virus representing a risk for the dissemination of the viral agent.

Epidemiology of Highly Pathogenic Avian Influenza Virus Strain Type H5N1

Highly pathogenic avian influenza (HPAI) is a severe disease of poultry. It is highly transmissible with a flock mortality rate approaching 100% in vulnerable species (Capua et al. 2007a). Due to the potentially disastrous impact the disease can have on affected poultry sectors, HPAI has received huge attention and is classified as a notifiable disease by the World Organisation for Animal Health (OIE).

Increased inducible nitric oxide synthase expression in organs is associated with a higher severity of H5N1 influenza virus infection

Background

The mechanisms of disease severity caused by H5N1 influenza virus infection remain somewhat unclear. Studies have indicated that a high viral load and an associated hyper inflammatory immune response are influential during the onset of infection. This dysregulated inflammatory response with increased levels of free radicals, such as nitric oxide (NO), appears likely to contribute to disease severity. However, enzymes of the nitric oxide synthase (NOS) family such as the inducible form of NOS (iNOS) generate NO, which serves as a potent anti-viral molecule to combat infection in combination with acute phase proteins and cytokines. Nevertheless, excessive production of iNOS and subsequent high levels of NO during H5N1 infection may have negative effects, acting with other damaging oxidants to promote excessive inflammation or induce apoptosis.

Methodology/Principal Findings

There are dramatic differences in the severity of disease between chickens and ducks following H5N1 influenza infection. Chickens show a high level of mortality and associated pathology, whilst ducks show relatively minor symptoms. It is not clear how this varying pathogenicty comes about, although it has been suggested that an overactive inflammatory immune response to infection in the chicken, compared to the duck response, may be to blame for the disparity in observed pathology. In this study, we identify and investigate iNOS gene expression in ducks and chickens during H5N1 influenza infection. Infected chickens show a marked increase in iNOS expression in a wide range of organs. Contrastingly, infected duck tissues have lower levels of tissue related iNOS expression.

Conclusions/Significance

The differences in iNOS expression levels observed between chickens and ducks during H5N1 avian influenza infection may be important in the inflammatory response that contributes to the pathology. Understanding the regulation of iNOS expression and its role during H5N1 influenza infection may provide insights for the development of new therapeutic strategies in the treatment of avian influenza infection.

Experimental studies of the role of the little raven (Corvus mellori) in surveillance for West Nile virus in Australia

OBJECTIVE

To study the potential role of an Australian corvid, the little raven (Corvus mellori), in the surveillance for exotic West Nile virus (WNV) in Australia.

METHOD

In a series of trials, little ravens were infected with WNV (strain 4132 New York 1999) and Kunjin virus (strain K42886) by the intramuscular route. They were observed for 20 days during which blood and swab samples were taken for virus isolation. Tissue samples were taken from ravens humanely killed during the acute infection period, and at the termination of the trials, for virus isolation, histopathology and immunohistochemistry.

RESULTS

Ravens infected with WNV became mildly ill, but all recovered and seroconverted. Blood virus titres peaked around 3 to 4 days after inoculation at levels between 10(3.0) to 10(7.5) plaque forming units/mL. Virus or viral antigen was detected in spleen, liver, lung, kidney, intestine, testis and ovary by virus isolation and/or immunohistochemistry. WNV was detected in oral and cloacal swabs from 2 to 7 days post inoculation. The molecular and pathogenic characteristics of the inocula were consistent with them being of high virulence, as expected for this isolate. Ravens infected with Kunjin virus developed viraemia and seroconverted, although they did not develop disease.

CONCLUSIONS

Little ravens do not develop severe disease in response to virulent WNV infection and for this reason may not be important sentinel hosts in the event of an outbreak of WNV, as in North America. However, as they have relatively high viraemias, they may be able to support virus cycles.

Comparative pathology of select agent influenza a virus infections

Influenza A virus infections may spread rapidly in human populations and cause variable mortality. Two of these influenza viruses have been designated as select agents: 1918 H1N1 virus and highly pathogenic avian influenza (HPAI) virus. Knowledge of the pathology of these virus infections in humans, other naturally infected species, and experimental animals is important to understand the pathogenesis of influenza, to design appropriate models for evaluation of medical countermeasures, and to make correct diagnoses. The most important complication of influenza in humans is viral pneumonia, which often occurs with or is followed by bacterial pneumonia. Viremia and extrarespiratory disease are uncommon. HPAI viruses, including HPAI H5N1 virus, cause severe systemic disease in galliform species as well as in anseriform species and bird species of other orders. HPAI H5N1 virus infection also causes severe disease in humans and several species of carnivores. Experimental animals are used to model different aspects of influenza in humans, including uncomplicated influenza, pneumonia, and virus transmission. The most commonly used experimental animal species are laboratory mouse, domestic ferret, and cynomolgus macaque. Experimental influenza virus infections are performed in various other species, including domestic pig, guinea pig, and domestic cat. Each of these species has advantages and disadvantages that need to be assessed before choosing the most appropriate model to reach a particular goal. Such animal models may be applied for the development of more effective antiviral drugs and vaccines to protect humans from the threat of these virus infections.