Host immune responses of ducks infected with H5N1 highly pathogenic avian influenza viruses of different pathogenicities

Pathogenicity of Duck Adenovirus Type 3 in Chickens

Duck adenovirus Type 3 (DAdV-3) severely affects the health of ducks; however, its pathogenicity in chickens remains unknown. The objectives of this study were to evaluate the pathogenicity and major pathological changes caused by DAdV-3 in chickens. Viral DNA was extracted from the liver of the Muscovy duck, and the fiber-2 and hexon fragments of DAdV-3 were amplified through polymerase chain reaction (PCR). The evolutionary tree revealed that the isolated virus belonged to DAdV-3, and it was named HE-AN-2022. The mortality rate of chicks that received inoculation with DAdV-3 subcutaneously via the neck was 100%, while the mortality rate for eye-nose drop inoculation was correlated with the numbers of infection, with 26.7% of chicks dying as a result of exposure to multiple infections. The main symptoms exhibited prior to death were hepatitis-hydropericardium syndrome (HHS), ulceration of the glandular stomach, and a swollen bursa with petechial hemorrhages. A histopathological examination revealed swelling, necrosis, lymphocyte infiltration, and basophilic inclusion bodies in multiple organs. Meanwhile, the results of quantitative real-time PCR (qPCR) demonstrated that DAdV-3 could affect most of the organs in chickens, with the gizzard, glandular stomach, bursa, spleen, and liver being the most susceptible to infection. The surviving chicks had extremely high antibody levels. After the chickens were infected with DAdV-3 derived from Muscovy ducks, no amino acid mutation was observed in the major mutation regions of the virus, which were ORF19B, ORF66, and ORF67. On the basis of our findings, we concluded that DAdV-3 infection is possible in chickens, and that it causes classic HHS with ulceration of the glandular stomach and a swollen bursa with petechial hemorrhages, leading to high mortality in chickens. The major variation domains did not change in Muscovy ducks or in chickens after infection. This is the first study to report DAdV-3 in chickens, providing a new basis for preventing and controlling this virus.

Genetic characteristics of waterfowl-origin H5N6 highly pathogenic avian influenza viruses and their pathogenesis in ducks and chickens

Waterfowl, such as ducks, are natural hosts for avian influenza viruses (AIVs) and act as a bridge for transmitting the virus to humans or susceptible chickens. Since 2013, chickens and ducks have been threatened by waterfowl-origin H5N6 subtype AIVs in China. Therefore, it is necessary to investigate the genetic evolution, transmission, and pathogenicity of these viruses. In this study, we determined the genetic characteristics, transmission, and pathogenicity of waterfowl-origin H5N6 viruses in southern China. The hemagglutinin (HA) genes of H5N6 viruses were classified into the MIX-like branch of clade 2.3.4.4h. The neuraminidase (NA) genes belonged to the Eurasian lineage. The PB1 genes were classified into MIX-like and VN 2014-like branches. The remaining five genes were clustered into the MIX-like branch. Therefore, these viruses belonged to different genotypes. The cleavage site of the HA proteins of these viruses was RERRRKR/G, a molecular characteristic of the H5 highly pathogenic AIV. The NA stalk of all H5N6 viruses contained 11 amino acid deletions at residues 58-68. All viruses contained 627E and 701D in the PB2 proteins, which were molecular characteristics of typical bird AIVs. Furthermore, this study showed that Q135 and S23 viruses could replicate systematically in chickens and ducks. They did not cause death in ducks but induced mild clinical signs in them. All the infected chickens showed severe clinical signs and died. These viruses were shed from the digestive and respiratory tracts and transmitted horizontally in chickens and ducks. Our results provide valuable information for preventing H5N6 avian influenza outbreaks.

Genetic characterization and pathogenicity of H7N9 highly pathogenic avian influenza viruses isolated from South China in 2017

Since 2017, the new H7N9 highly pathogenic avian influenza viruses (HPAIVs) have been responsible for more than 200,000 cases of chicken infection and more than 120,000 chicken deaths in China. Our previous study found that the Q26 was chicken-origin H7N9 HPAIV. In this study, we analyzed the genetic characterization of Q24, Q65, Q66, Q85, and Q102 H7N9 avian influenza viruses isolated from Guangdong, China in 2017. Our results showed that these viruses were highly pathogenic and belonged to two different genotypes, which suggested they occurred genetic reassortant. To investigate the pathogenicity, transmission, and host immune responses of H7N9 virus in chickens, we selected Q24 and Q26 viruses to inoculate chickens. The Q24 and Q26 viruses killed all inoculated chickens within 3 days and replicated effectively in all tested tissues. They were efficiently transmitted to contact chickens and killed them within 4 days through direct contact. Furthermore, we found that the expressions of several immune-related genes (e.g., TLR3, TLR7, MDA5, MAVS, IFN-β, IL-6, IL-8, OAS, Mx1, MHC I, and MHC II) were upregulated obviously in the lungs and spleen of chickens inoculated with the two H7N9 viruses at 24 h post-inoculation (HPI). Among these, IL-6 and IFN-β in lungs were the most upregulated (by 341.02-381.48-fold and 472.50-500.56-fold, respectively). These results suggest that the new H7N9 viruses isolated in 2017, can replicate and transmit effectively and trigger strong immune responses in chickens, which helps us understand the genetic and pathogenic variations of H7N9 HPAIVs in China.

Differential proteome response to H5N1 highly pathogenic avian influenza (HPAI) viruses infection in duck

Ducks and wild aquatic birds are the natural reservoirs of avian influenza viruses. However, the host proteome response that causes disease in vivo by the H5N1 HPAI virus is still unclear. This study presented a comprehensive analysis of the proteome response in Muscovy duck lung tissue during 3 days of infection with either a highly virulent DK383 or an avirulent DK212. An unbiased strategy- isobaric tags for relative and absolute quantitation (iTRAQ) in conjunction with high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) was utilized to investigate the infection mechanism. Pathways derived from analysis of 292 significantly altered proteins may contribute to the high pathogenic nature and disease progression of H5N1 viruses. Global proteome profiles indicated improved correlation with the virus titers and gene expression patterns between the two strains of the H5N1 virus. DK383 replicated more efficiently and induced a stronger response specific to severe disease. While proteins involved in the immune response of neutrophils were increased markedly by DK383, DK212 evoked a distinct response characterized by an increase in proteins involved in the maturation of dendritic cells, adhesion of phagocytes, and immune response of macrophages. The differentially activated Akt/mTOR/p70S6K pathway might involve in the host response to H5N1 viruses. Therefore, systematically integrated with datasets from primary genomic and virus titer results, proteomic analyses may help reveal the potential pathogenesis.

Evolution of RNA sensing receptors in birds

Birds are important hosts for many RNA viruses, including influenza A virus, Newcastle disease virus, West Nile virus and coronaviruses. Innate defense against RNA viruses in birds involves detection of viral RNA by pattern recognition receptors. Several receptors of different classes are involved, such as endosomal toll-like receptors and cytoplasmic retinoic acid-inducible gene I-like receptors, and their downstream adaptor proteins. The function of these receptors and their antagonism by viruses is well established in mammals; however, this has received less attention in birds. These receptors have been characterized in a few bird species, and the completion of avian genomes will permit study of their evolution. For each receptor, functional work has established ligand specificity and activation by viral infection. Engagement of adaptors, regulation by modulators and the supramolecular organization of proteins required for activation are incompletely understood in both mammals and birds. These receptors bind conserved nucleic acid agonists such as single- or double-stranded RNA and generally show purifying selection, particularly the ligand binding regions. However, in birds, these receptors and adaptors differ between species, and between individuals, suggesting that they are under selection for diversification over time. Avian receptors and signalling pathways, like their mammalian counterparts, are targets for antagonism by a variety of viruses, intent on escape from innate immune responses.

Pathogenicity and innate response to Avibacterium paragallinarum in chickens

Infectious coryza (IC) is an acute infectious upper respiratory disease in chickens. Recently, the prevalence of IC has increased in China. In this study, to clarify the pathogenic mechanism and innate immune response of Avibacterium paragallinarum (A. paragallinarum), an infection experiment with A. paragallinarum was conducted. Our results showed that the whole course of IC was approximately 7 d. The clinical signs score was highest at 3 dpi and decreased from 5 dpi. A large amount of mucus and exudates was found in the infraorbital sinuses and nasal cavity. The A. paragallinarum contents in blood remained the highest, reaching 9.16 × 10⁵ CFU/g at 5 dpi, which indicated that A. paragallinarum could rapidly invade the host, replicate in the blood and cause bacteremia. A. paragallinarum targets the upper respiratory tract. The infiltration of inflammatory cells, macrophages, and heterophilic granulocytes was only observed in the nasal cavity and infraorbital sinus. The Tlr4 and Nod1 pathways were activated and induced proinflammatory responses in chickens after infection with A. paragallinarum. The expression of Il1β and Il6 in the nasal cavity was significantly higher than that in the spleen, and it was consistent with the gross lesions and pathological changes. In particular, the expression of Il6 increased 229.07-fold at 1 dpi in the nasal cavity and increased 3.12-fold in the spleen. The high level of proinflammatory cytokines in the nasal cavity at an early stage of infection may be the main factor related to acute upper respiratory inflammation in chickens. These findings provide a reference for the occurrence and development of diseases mediated by A. paragallinarum.

Pathogenicity and Immune Responses in Specific-Pathogen-Free Chickens During Fowl Adenovirus Serotype 4 Infection

Hydropericardium-hepatitis syndrome, a recently emerged disease of chickens, is caused by some strains of fowl adenovirus serotype 4 (FAdV-4). However, the relationship between the immune response and cytokine expression during FAdV-4 infection is largely unknown. In this study, our data showed that all chickens exhibited typical clinical signs and lesions and that the viral load was significantly increased in both the liver and thymus following FAdV-4 infection. We also found that the appearance of tissue lesions in the liver and thymus was consistent with the viral copy numbers, indicating that virus replication in systemic organs closely correlated with disease progression. In addition, the effects of FAdV-4 infection on the transcription of some avian cytokines were studied in vivo. In general, expression of the proinflammatory cytokines interleukin (IL)-2 and interferon (IFN)-α and IFN-β in the liver and thymus was strongly upregulated. Interestingly, the expression of IL-2 was the most highly upregulated. Expression of the anti-inflammatory cytokines IL-4, IL-10, and transforming growth factor (TGF)-β1 and TGF-β2, were also upregulated. Moreover, we investigated both the humoral and cellular immune responses in chickens infected with FAdV-4. Compared to those in the noninfected chickens, the antibody levels in chickens infected with FAdV-4 were significantly increased within 30 days postinfection. In addition, the ratio of CD4+/CD8+ T cells was decreased in FAdV-4-infected chickens. Taken together, these findings increase our understanding of the pathogenesis of FAdV-4 in chickens and provide a foundation for additional pathogenesis studies.

Differences in Highly Pathogenic H5N6 Avian Influenza Viral Pathogenicity and Inflammatory Response in Chickens and Ducks

Infection with H5N6 highly pathogenic avian influenza virus caused high mortality in chickens, while ducks often appear to be asymptomatic. But, some recent H5Nx subtype viruses could cause high mortality in ducks. The variation between different species and the mechanisms by which some H5Nx viruses cause death in ducks requires investigation to identify the key processes in influenza susceptibility and pathogenesis. Here, we characterized two representative H5N6 viruses, A/Pavo cristatus/Jiangxi/JA1/2016 (JA1) and A/Anas crecca/shanghai/SH1/2016 (SH1), and compared their pathogenicity and expression profiles of immune-related genes in chickens and ducks to identify the elements of the host immune-related response that were involved in disease lethality. Results suggested that H5N6 HPAIVs had higher pathogenic and inflammatory effect in chickens than in ducks. Importantly, the TNF-α, IL-6, IFN-γ and iNOS levels were significantly higher in the lung of SH1 infected chickens compared to those of ducks. And we found higher systemic levels of IL-6 induced by JA1 in chickens than in ducks. In addition, our experiments demonstrated that JA1 was associated with greater pathogenicity in ducks were accompanied by the excessive expression of iNOS in the brain. These results are helpful to understand the relationship between the pathogenicity of H5N6 AIVs and inflammatory responses to them in chickens and ducks.

The Biological Characteristics of Novel H5N6 Highly Pathogenic Avian Influenza Virus and Its Pathogenesis in Ducks

Clade 2.3.4.4 H5Nx highly pathogenic avian influenza viruses (HPAIVs) have caused outbreaks in poultry in the world. Some of these viruses acquired internal genes from other subtype avian influenza viruses (AIVs) such as H9 and H6 for the generation of novel reassortant viruses and continually circulated in poultry. Here, we applied a duck-origin virus DK87 and a chicken-origin virus CK66 to assess the biological characteristics of novel reassortant H5N6 HPAIVs and its pathogenesis in ducks. A genetic analysis indicated that the HA genes of the two H5N6 HPAIVs were closely related to the H5 viruses of clade 2.3.4.4 circulating in Eastern Asia and classified into H5 AIV/Eastern Asia (EA)-like lineage. Their NA genes fell into Eurasian lineage had close relationship with those of H5N6 viruses circulating in China, Laos, Vietnam, Japan, and Korea. All internal genes of DK87 were aggregated closely with H5 AIV/EA-like viruses. The internal genes (PB1, PA, NP, M, and NS) of CK66 were derived from H9N2 AIV/SH98-like viruses and the PB2 were derived from H5 AIV/EA-like viruses. These results indicate that clade 2.3.4.4 H5N6 AIVs have continually evolved and recombined with the H9N2 viruses circulating in Southern China. Pathogenicity test showed that the two viruses displayed a broader tissue distribution in ducks and caused no clinical signs. These results indicated that ducks were permissive for the replication of the chicken-origin reassortant virus CK66 without prior adaptation, but the duck-origin virus DK87-inoculated ducks showed significantly higher viral titers in some organs than the CK66-inoculated ducks at 5 day post-inoculated (DPI). The recovery of viruses from oropharyngea and cloacal swabs of contacted ducks indicated that they transmitted in native ducks by direct contact. Quantitative reverse transcription PCR (qRT-PCR) results revealed that the immune-relative genes (PRRs, IFNs, Mx-1, IL-6, and IL-8) in the lungs of inoculated ducks were expressed regardless of virus origin, but the expression of these genes was significantly higher in response to infection with the DK87 virus compared to the CK66 virus at 3 DPI. Overall, we should provide further insights into how clade 2.3.4.4 H5N6 AIVs undergo genetic and pathogenic variations to prevent outbreaks of this disease.

Functions of interleukin-6 in ovulation of female climbing perch, Anabas testudineus

In mammals, interleukin 6 (IL-6) has an important function during ovulation, however, the functions of IL-6 in fish have not been elucidated. In the present study, there was quantification of de novo synthesis of ovarian IL-6 and tumor necrosis factor-alpha (TNFα) in control and hCG-treated fish and results were compared with those from an in vitro study where there was evaluation of the regulatory functions of gonadotropins and TNFα of IL-6 secretions. Relatively greater concentrations of ovarian IL-6 at the post-GVBD (post-germinal vesicle breakdown) stage indicates IL-6 modulates ovulatory processes. The hCG-induced increase in relative abundance of IL-6 (in vitro) mRNA transcript and secretion from the ovary were attenuated when there was administration of the inhibitor of TNFα secreting enzyme, TAPI-I, which indicates TNFα modulates IL-6 secretion. Treatments with IL-6 induced a marked increase in ovulation rate in vitro when there was induction of activating matrix metalloproteinase (MMP). Furthermore, treatment with IL-6 resulted in production of prostaglandin as indicated by the IL-6 induced increase in the abundance of ptgs2 mRNA transcript in the ovary of Anabas testudineus. Furthermore, results indicate the source of IL-6 in the ovary is the granulosa cells with secretion of IL-6 being induced by the additions of hCG and TNFα in the medium. There was also an IL-6-induced increase in abundance of receptors (IL-6 Rα and gp130) to which it binds indicating IL-6 autoregulates this population of receptors. Results from this study, for the first time, elucidate the reproductive functions of IL-6 in a teleost fish.

Duck TRIM32 Functions in IFN-β Signaling Against the Infection of H5N6 Highly Pathogenic Avian Influenza Virus

In mammals, tripartite motif 32 (TRIM32) is essential for regulating host innate immune responses to viral infections. However, the antiviral effect of TRIM32 in birds has not been reported. Here, we cloned the full-length duck TRIM32 (duTRIM32) cDNA from total spleen RNA of Peking duck. DuTRIM32 consists of 682 amino acids and has 95.5% similarity in amino acid sequences with chicken TRIM32 and 84.9% similarity with human TRIM32, respectively. DuTRIM32 mRNA was found to be ubiquitously expressed in all tested tissues from healthy ducks. Overexpression of duTRIM32 significantly activated the IFN-β promoter and upregulated the mRNA levels of IFN-β, IRF7, and Mx, which indicates that duTRIM32 is involved in the type I IFN pathway. Furthermore, duTRIM32 was found to directly interact with duck STING (duSTING) and to contribute to the expression of IFN-β mediated by duSTING. The mRNA level of duTRIM32 was significantly upregulated in the lungs and spleens of H5N6 highly pathogenic avian influenza virus (HPAIV) infected ducks 3 days post-infection (DPI). Furthermore, overexpression of duTRIM32 could inhibit the replication of H5N6 HPAIV in duck embryo fibroblasts (DEFs). Therefore, these results indicate that duTRIM32 is involved in the type I IFN pathway and exhibit an antiviral effect against H5N6 HPAIV infection.

Host Innate Immune Response of Geese Infected with Clade 2.3.4.4 H5N6 Highly Pathogenic Avian Influenza Viruses

Since 2014, highly pathogenic avian influenza (HPAI) H5N6 viruses have circulated in waterfowls and caused human infections in China, posing significant threats to the poultry industry and the public health. However, the genetics, pathogenicity and innate immune response of H5N6 HPAIVs in geese remain largely unknown. In this study, we analyzed the genetic characteristic of the two H5N6 viruses (GS38 and DK09) isolated from apparently healthy domestic goose and duck in live poultry markets (LPMs) of Southern China in 2016. Phylogenetic analysis showed that the HA genes of the two H5N6 viruses belonged to clade 2.3.4.4 and were clustered into the MIX-like group. The MIX-like group viruses have circulated in regions such as China, Japan, Korea, and Vietnam. The NA genes of the two H5N6 viruses were classified into the Eurasian sublineage. The internal genes including PB2, PB1, PA, NP, M, and NS of the two H5N6 viruses derived from the MIX-like. Therefore, our results suggested that the two H5N6 viruses were reassortants of the H5N1 and H6N6 viruses and likely derived from the same ancestor. Additionally, we evaluated the pathogenicity and transmission of the two H5N6 viruses in domestic geese. Results showed that both the two viruses caused serious clinical symptoms in all inoculated geese and led to high mortality in these birds. Both the two viruses were transmitted efficiently to contact geese and caused lethal infection in these birds. Furthermore, we found that mRNA of pattern recognition receptors (PRRs), interferons (IFNs), and stimulated genes (ISGs) exhibited different levels of activation in the lungs and spleens of the two H5N6 viruses-inoculated geese though did not protect these birds from H5N6 HPAIVs infection. Our results suggested that the clade 2.3.4.4 waterfowl-origin H5N6 HPAIVs isolated from LPMs of Southern China could cause high mortality in geese and innate immune-related genes were involved in the geese innate immune response to H5N6 HPAIVs infection. Therefore, we should pay more attention to the evolution, pathogenic variations of these viruses and enhance virological surveillance of clade 2.3.4.4 H5N6 HPAIVs in waterfowls in China.

Phylogeny, Pathogenicity, Transmission, and Host Immune Responses of Four H5N6 Avian Influenza Viruses in Chickens and Mice

H5Nx viruses have continuously emerged in the world, causing poultry industry losses and posing a potential public health risk. Here, we studied the phylogeny, pathogenicity, transmission, and immune response of four H5N6 avian influenza viruses in chickens and mice, which were isolated from waterfowl between 2013 and 2014. Their HA genes belong to Clade 2.3.4.4, circulated in China since 2008. Their NA genes fall into N6-like/Eurasian sublineage. Their internal genes originated from different H5N1 viruses. The results suggested that the four H5N6 viruses were reassortants of the H5N1 and H6N6 viruses. They cause lethal infection with high transmission capability in chickens. They also cause mild to severe pathogenicity in mice and can spread to the brain through the blood–brain barrier. During the infection, the viruses result in the up-regulation of PRRs and cytokine in brains and lungs of chickens and mice. Our results suggested that the high viral loads of several organs may result in disease severity in chickens and mice; there were varying levels of cytokines induced by the H5N6 viruses with different pathogenicity in chickens and mice.

Recombinant Duck Interferon Gamma Inhibits H5N1 Influenza Virus Replication In Vitro and In Vivo

The highly pathogenic H5N1 avian influenza virus (AIV) is widespread in waterfowl, causing enormous economic losses and posing a significant threat to public health. An increasing number of reagents have been identified to prevent the spread of influenza; however, there have been no reports on the anti-H5N1 effects of duck interferons, which exhibit antiviral activity against other viruses. Our aim was to investigate the antiviral effects of purified duck interferons. In this study, we successfully cloned and expressed duck interferon gamma (IFN-γ) in Escherichia coli. The antiviral effects of this recombinant duck IFN-γ (rDuIFN-γ) was assessed in vitro and in vivo. rDuIFN-γ displayed antiviral activity against vesicular stomatitis virus and AIV in duck embryo fibroblasts. Pretreating ducks with 3.4 × 10⁴ U rDuIFN-γ also partially decreased mortality from 70% to 30% and delayed onset in 2-day-old Peking ducks. Virus titers in tissues and viral shedding decreased, and the expression of interferon-stimulated genes increased in brain and spleen in rDuIFN-γ-treated ducks. These results indicate that duck IFN-γ has the potential to inhibit viral replication in ducks.

Immune-Related Gene Expression in Ducks Infected With Waterfowl-Origin H5N6 Highly Pathogenic Avian Influenza Viruses

Clade 2.3.4.4 H5 avian influenza viruses (AIVs) are widely prevalent and of significant concern to the poultry industry and public health in China. Nowadays, the clade 2.3.4.4 H5N6 virus has become a dominant AIV subtype among domestic ducks in southern China. We found that waterfowl-origin clade 2.3.4.4 H5N6 viruses (A/goose/Guangdong/16568/2016, GS16568 and A/duck/Guangdong/16873/2016, DK16873) isolated from southern China in 2016 could replicate in multiple organs of inoculated ducks. DK16873 virus caused mild infections and killed 2/5 of inoculated ducks, and GS16568 virus did not kill inoculated ducks. In addition, the two viruses could be transmitted via direct contact between ducks. DK16873 and GS16568 viruses killed 2/5 and 1/5 of contact ducks, respectively. Furthermore, ducks inoculated with the two H5N6 viruses exhibited different expressions of immune-related genes in their lungs. The expression of RIG-I, TLR3 and IL6 was significantly upregulated at 12 h post-inoculation (HPI) and most of the tested immune-related genes were significantly upregulated at 3 days post-inoculation (DPI). Notably, the expression of RIG-I and IL-6 in response to DK16873 virus was significantly higher than for GS16568 virus at 12 HPI and 3 DPI. Our research have provided helpful information about the pathogenicity, transmission and immune-related genes expression in ducks infected with new H5N6 AIVs.

Virulence of three European highly pathogenic H7N1 and H7N7 avian influenza viruses in Pekin and Muscovy ducks

Background

There is paucity of data on the virulence of highly pathogenic (HP) avian influenza viruses (AIV) H7 in ducks compared to HPAIV H5. Here, the virulence of HPAIV H7N1 (designated H7N1-FPV34 and H7N1-It99) and H7N7 (designated H7N7-FPV27) was assessed in Pekin and/or Muscovy ducklings after intrachoanal (IC) or intramuscular (IM) infection.

Results

The morbidity rate ranged from 60 to 100% and mortality rate from 20 to 80% depending on the duck species, virus strain and/or challenge route. All Muscovy ducklings inoculated IC with H7N7-FPV27 or H7N1-FPV34 exhibited mild to severe clinical signs resulting in the death of 2/10 and 8/10 ducklings, respectively. Also, 2/10 and 6/9 of inoculated Muscovy ducklings died after IC or IM infection with H7N1-It99, respectively. Moreover, 5/10 Pekin ducklings inoculated IC or IM with H7N1-It99 died. The level of virus detected in the oropharyngeal swabs was higher than in the cloacal swabs.

Conclusion

Taken together, HPAIV H7 cause mortality and morbidity in Muscovy and Pekin ducklings. The severity of disease in Muscovy ducklings depended on the virus strain and/or route of infection. Preferential replication of the virus in the respiratory tract compared to the gut merits further investigation.

Ducks induce rapid and robust antibody responses than chickens at early time after intravenous infection with H9N2 avian influenza virus

Background

Compared with chickens, ducks are normally resistant to avian influenza virus without clinical signs while they habor almost all subtypes of influenza A viruses. To date, however the mechanism for duck anti-influenza has not been completely understood. The H9N2 avian influenza virus (AIV) is the most prevalent subtype of influenza A virus that infects chickens and ducks in China. However, H9N2 AIV replication and the host immune response in these domestic birds has not been systematically investigated.

Methods

In the present study, we compared the kinetics and magnitudes of antibody responses in chickens and ducks after infection with H9N2 AIV by the intranasal route or intravenous route. Furthermore, we determined the viral replication and distribution in chickens and ducks after infection with H9N2 AIV by the intravenous route.

Results

Our results revealed that the antibody response was rapid and robust in ducks than in chickens at early time (2-3dpi) after intravenous infection with H9N2 AIVs, while delayed and lower antibody detected in ducks than in chickens after intranasal infection with H9N2 AIVs. The virus was detected in multiple organs tissues in chickens but not in ducks infected by the intravenous route.

Conclusions

Our results provide the evidence that humoral immune response could play a critical role in duck resistance for influenza, which expands our knowledge on duck anti-influenza characteristics.

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.

Duck innate immune responses to high and low pathogenicity H5 avian influenza viruses

Ducks are the reservoir host of influenza A viruses, and are permissive for replication of most strains, yet can elicit robust innate immune responses to highly pathogenic strains. Tissue tropism and viral amino acid differences affect virulence, but we have limited knowledge about how viral differences influence the host innate immune response. Here we compare the innate immune response in Pekin ducks to a recombinant highly-pathogenic avian influenza (HPAI) H5N1 virus and a naturally arising attenuated variant of this strain that differs at one amino acid in polymerase A (T515A), as well as ducks infected with two different H5 strains of low pathogenic avian influenza (LPAI). Using qPCR we examined the relative abundance of transcripts for RIG-I and interferon-beta (IFNβ), and downstream interferon stimulated genes (ISGs). The polymerase PA (T515A) mutation did not significantly affect replication in vivo but greatly attenuated host interferon responses. ISG induction was robust for both H5N1 strains, but was three times lower for the PA mutant strain. Low pathogenic viruses elicited detectable induction of RIG-I, IFNβ and ISGs in lung and intestine tissues that correlated with the recovery of viruses from tracheal or cloacal swabs. Several genes in the MAVS signaling pathway were also upregulated by H5N1, which contributed to further amplification of the signal. We also examined hematoxylin-eosin stained tissue sections and observe evidence of lung pathology and splenocyte depletion with both H5N1 viruses at 3 dpi, and recovery by 6 dpi. However, for both H5N1 strains we observed inflammation around neurons in brain, with increased cytokine expression in some individuals. Our findings reveal HPAI H5N1 viruses induced stronger innate immune responses to the infection, while LPAI viruses elicit a milder response.

IFN and cytokine responses in ducks to genetically similar H5N1 influenza A viruses of varying pathogenicity

Ducks, the reservoir host, are generally permissive to influenza A virus infection without disease symptoms. This natural ecology was upset by the emergence of H5N1 strains, which can kill ducks. To better understand host-virus interactions in the reservoir host, and influenza strain-specific molecular contributions to virulence, we infected White Pekin ducks with three similar H5N1 viruses, with known differences in pathogenicity and replication rate. We quantified viral replication and innate immune gene activation by qPCR, in lung and spleen tissues, isolated on each of the first 3 days of infection. The three viruses replicated well, as measured by accumulation of matrix gene transcript, and viral load declined over time in the spleen. The ducks produced rapid, but temporally limited, IFN and cytokine responses, peaking on the first day post-infection. IFN and proinflammatory cytokine gene induction were greater in response to infection with the more lethal viruses, compared to an attenuated strain. We conclude that a well-regulated IFN response, with the ability to overcome early viral immune inhibition, without hyperinflammation, contributes to the ability of ducks to survive H5N1 influenza replication in their airways, and yet clear systemic infection and limit disease.

Fowl Adenovirus Serotype 4 SD0828 Infections Causes High Mortality Rate and Cytokine Levels in Specific Pathogen-Free Chickens Compared to Ducks

Hydropericardium syndrome and inclusion body hepatitis, together called hydropericardium-hepatitis syndrome, are acute infectious diseases found in chickens. These diseases are caused primarily by fowl adenovirus serotype 4 (FAdV-4) strains. In this study, we isolated a FAdV-4 strain (SD0828) from clinically diseased chickens and phylogenetically analyzed the L1 loops of the hexon protein sequences in 3-week-old specific pathogen-free chickens and ducks infected intramuscularly and orally, determining differences in the pathogenicity by observing clinical signs and gross and histological lesions. We also detected the viral load in tissue samples. Postinfection necropsy showed that all chickens but no ducks exhibited typical necropsy lesions. Additionally, all chickens infected intramuscularly died within 2 days postinfection (dpi), and all those infected orally died within 5 dpi, whereas no infected ducks died before 28 dpi. Quantitative real-time polymerase chain reaction analysis was used to determine the viral load in the tissues of hearts, livers, spleens, lungs, and kidneys and in cloacal cotton swabs from infected chickens and ducks at 1, 2, 3, 5, 7, 14, 21, and 28 dpi. The greatest number of viral DNA copies was found in the livers of infected chickens, yet no virus was found in any samples from infected ducks. In addition, the viral load increased over time in both chicken and duck embryo fibroblasts (CEFs and DEFs, respectively); in the former, replication speed was significantly greater than in the latter. Innate immune responses were also studied, both in vivo and in vitro. In CEFs, DEFs, and chickens infected intramuscularly, but not in infected ducks, mRNA expression levels of proinflammatory cytokines (interleukin-6 and -8) and interferon-stimulated genes (Mx and OAS) were significantly upregulated. Although some cytokines showed significant upregulation in the oral chickens, most did not change significantly. Finally, the duck retinoic acid-inducible gene I and its caspase activation and recruitment domain both had significant antiviral functions in CEFs, particularly after 24 h postinfection. Taken together, this research provides new insights into the interactions between FAdV-4 and the innate immune systems of studied hosts (chickens and ducks).

An Egyptian HPAI H5N1 isolate from clade 2.2.1.2 is highly pathogenic in an experimentally infected domestic duck breed (Sudani duck)

The highly pathogenic avian influenza (HPAI) H5N1 viruses continue to cause major problems in poultry and can, although rarely, cause human infection. Being enzootic in domestic poultry, Egyptian isolates are continuously evolving, and novel clades vary in their pathogenicity in avian hosts. Considering the importance of domestic ducks as natural hosts of HPAI H5N1 viruses and their likelihood of physical contact with other avian hosts and humans, it is of utmost importance to characterize the pathogenicity of newly emerged HPAI strains in the domestic duck. The most recently identified Egyptian clade 2.2.1.2 HPAI H5N1 viruses have been isolated from naturally infected pigeons, turkeys and humans. However, essentially nothing is known about their pathogenicity in domestic ducks. We therefore characterized the pathogenicity of an Egyptian HPAI H5N1 isolate A/chicken/Faquos/amn12/2011 (clade 2.2.1.2) in Sudani duck, a domestic duck breed commonly reared in Egypt. While viral transcription (HA mRNA) was highest in lung, heart and kidney peaking between 40 and 48 hpi, lower levels were detected in brain. Weight loss of infected ducks started at 16 hpi and persisted until 120 hpi. The first severe clinical signs were noted by 32 hpi and peaked in severity at 72 and 96 hpi. Haematological analyses showed a decline in total leucocytes, granulocytes, platelets and granulocyte/lymphocyte ratio, but lymphocytosis. Upon necropsy, lesions were obvious in heart, liver, spleen and pancreas and consisted mainly of necrosis and petechial haemorrhage. Histologically, lungs were the most severely affected organs, whereas brain only showed mild neuronal degeneration and gliosis at 48 hpi despite obvious neurological clinical signs. Taken together, our results provide first evidence that this HPAI H5N1 isolate (clade 2.2.1.2) is highly pathogenic to Sudani ducks and highlight the importance of this breed as potential reservoir and disseminator of HPAI strains from this clade.

Molecular Cloning, Characterization, and Anti-avian Pathogenic Escherichia coli Innate Immune Response of the Cherry Valley Duck CIITA Gene

Class II major histocompatibility complex (MHC-II) transactivator (CIITA) is a member of the pattern recognition receptor in cytoplasm, which is involved in host innate immune responses. In this study, the full-length cDNA of Cherry Valley duck CIITA (duCIITA) was cloned from the spleen of healthy Cherry Valley ducks for the first time. The CDs of duCIITA have 3648 bp and encode 1215 amino acids. The homology analysis of CIITAs amino acid sequence showed that the duCIITA has the highest identity with the Anas platyrhynchos (94.9%), followed by Gallus gallus and Meleagris gallopavo. Quantitative real-time PCR analysis indicated that duCIITA mRNA has a broad expression level in healthy Cherry Valley duck tissues. It was highly expressed in the lung and cerebellum, and lowly expressed in the rectum and esophagus. After the avian pathogenic Escherichia coli (APEC) O1K1 infection, the ducks exhibited the typical clinical symptoms, and a severe fibrinous exudate in the heart and liver surface was observed. Meanwhile, a significant up-regulation of duCIITA was detected in the infected liver. The inflammatory cytokines IL-1β, IL-6, and IL-8 have a significant up-regulation in the infected liver, spleen and brain. In addition, knockdown of the duCIITA reduces antibacterial activity and inflammatory cytokine production of the duck embryo fibroblast cells. Our research is the first study of the cloning, tissue distribution, and antibacterial immune responses of duCIITA, and these findings imply that duCIITA was an important receptor, which was involved in the early stage of the antibacterial innate immune response to APEC O1K1 infection of Cherry Valley duck.

Immune Responses of Chickens Infected with Wild Bird-Origin H5N6 Avian Influenza Virus

Since April 2014, new infections of H5N6 avian influenza virus (AIV) in humans and domestic poultry have caused considerable economic losses in the poultry industry and posed an enormous threat to human health worldwide. In previous research using gene sequence and phylogenetic analysis, we reported that H5N6 AIV isolated in February 2015 (ZH283) in Pallas’s sandgrouse was highly similar to that isolated in a human in December 2015 (A/Guangdong/ZQ874/2015), whereas a virus (i.e., SW8) isolated in oriental magpie-robin in 2014 was highly similar to that of A/chicken/Dongguan/2690/2013 (H5N6). However, the pathogenicity, transmissibility, and host immune-related response of chickens infected by those wild bird-origin H5N6 AIVs remain unknown. In response, we examined the viral distribution and mRNA expression profiles of immune-related genes in chickens infected with both viruses. Results showed that the H5N6 AIVs were highly pathogenic to chickens and caused not only systemic infection in multiple tissues, but also 100% mortality within 3–5 days post-infection. Additionally, ZH283 efficiently replicated in all tested tissues and transmitted among chickens more rapidly than SW8. Moreover, quantitative real-time polymerase chain reaction analysis showed that following infection with H5N6, AIVs immune-related genes remained active in a tissue-dependent manner, as well as that ZH283 induced mRNA expression profiles such as TLR3, TLR7, IL-6, TNF-α, IL-1β, IL-10, IL-8, and MHC-II to a greater extent than SW8 in the tested tissues of infected chickens. Altogether, our findings help to illuminate the pathogenesis and immunologic mechanisms of H5N6 AIVs in chickens.

Host Differences Affecting Resistance and Susceptibility of the Second Generation of a Pekin Duck Flock to Duck Hepatitis A Virus Genotype 3

Earlier work suggested the possibility to anti duck hepatitis A virus genotype 3 (DHAV-3) using the resistance breeding strategy. Here, we report the creation of the second generations of a resistant Pekin duck flock (designated Z8R2) and a highly susceptible Pekin duck flock (designated Z8S2) and the investigation of their responses to DHAV-3. Experimental infection with DHAV-3 at 7 days of age resulted in a high mortality (66.3%) in 11 susceptible Z8S2 families and an extremely low mortality rate (2.67%) in 32 Z8R2 families, indicating that Z8R2 exhibits strong resistance to DHAV-3, while Z8S2 is highly susceptible to the virus. Detection of DHAV-3 in the liver between 1 and 60 hours post inoculation (hpi) suggests that DHAV-3 can be replicated rapidly and efficiently in the liver of Z8S2, whereas the replication of the virus in the liver of Z8R2 is suppressed greatly. High levels of serum biochemical markers (e.g., ALT, AST, ALP and GGT) were detected in Z8S2 at 24 hpi, which were significantly higher than those in Z8R2. Analysis of transcripts in the liver revealed that the expression levels of several pattern recognition receptors (PRRs) (e.g., TLR4/7, RIG-1 and MDA5) and cytokines (e.g., IL-2, IL-6, IL-8, IFN-α, and IFN-γ) in Z8S2 were significantly higher than those in Z8R2 at 12 and 24 hpi. Together these findings suggest that Z8R2 and Z8S2 Pekin ducks, which were derived from the same Z8 line, exhibit disparate pathogenic outcomes following DHAV-3 infection. Therefore, it is possible to select a Pekin duck flock resistant to DHAV-3 employing the strategy described here. It is likely that the high viral load and the strong inflammatory response correlate with the high susceptibility of Z8S2 Pekin ducks to DHAV-3.

Age-related changes and distribution of T cell markers (CD3 and CD4) and toll-like receptors(TLR2, TLR3,TLR4 and TLR7) in the duck lymphoid organs

T lymphocytes and Toll-like receptors have been confirmed to have correlation with the ability to resistance to pathogenic challenges and play an important role in duck immune system. However, the information of ontogeny of T lymphocytes and Toll-like receptors is scarcely in duck. Therefore, to address these questions, we report the development and distribution of CD3 and CD4 by immunocytochemistry and the age-related mRNA level of duck T cell markers (CD3 and CD4) and Toll-like receptors (TLR2, TLR3, TLR4 and TLR7) by real time quantitative PCR in duck lymphoid organs (thymus, bursa of Fabricius and spleen). Results indicated that CD3 and CD4 positive cells can be observed in all test organs and partly change in an age-related way. CD4 positive T cell of duck spleen mainly distributed in periarterial lymphatic sheaths and red pulp, not in white pulp. Both of CD3 and CD4 were experienced significant increased wave twice in duck lymphoid organs and T cell dependent cellular immunity of duck may well established until 5 weeks old. The mRNA expression levels of duck TLRs were age and organ dependent, and duck TLR3 and TLR7 were significantly lower abundance in the spleen but higher in thymus and bursa of Fabricius, respectively. This study provide the essential knowledge of the ontogeny of T cells and Toll-like receptors in duck, which may shed lights on the T-cell mediate immunity and innate immunity in duck.

Emerging avian influenza infections: Current understanding of innate immune response and molecular pathogenesis

The highly pathogenic avian influenza viruses (HPAIVs) cause severe disease in gallinaceous poultry species, domestic ducks, various aquatic and terrestrial wild bird species as well as humans. The outcome of the disease is determined by complex interactions of multiple components of the host, the virus, and the environment. While the host-innate immune response plays an important role for clearance of infection, excessive inflammatory immune response (cytokine storm) may contribute to morbidity and mortality of the host. Therefore, innate immunity response in avian influenza infection has two distinct roles. However, the viral pathogenic mechanism varies widely in different avian species, which are not completely understood. In this review, we summarized the current understanding and gaps in host-pathogen interaction of avian influenza infection in birds. In first part of this article, we summarized influenza viral pathogenesis of gallinaceous and non-gallinaceous avian species. Then we discussed innate immune response against influenza infection, cytokine storm, differential host immune responses against different pathotypes, and response in different avian species. Finally, we reviewed the systems biology approach to study host-pathogen interaction in avian species for better characterization of molecular pathogenesis of the disease. Wild aquatic birds act as natural reservoir of AIVs. Better understanding of host-pathogen interaction in natural reservoir is fundamental to understand the properties of AIV infection and development of improved vaccine and therapeutic strategies against influenza.

Dietary Administration of Bacillus subtilis Enhances Growth Performance, Immune Response and Disease Resistance in Cherry Valley Ducks

Given the promising results of applying Bacillus subtilis (B.subtilis) as a probiotic in both humans and animals, the aim of this study was to systematically investigate the effects of B. subtilis on growth performance, immune response and disease resistance in Cherry Valley ducks. At 28 d post-hatch (dph), ducks fed a diet with B. subtilis weighed significantly more, had higher relative immune organ weights (e.g., bursa of Fabricius, thymus, and spleen), and exhibited greater villus heights, villus height to crypt depth ratios (duodenum and jejunum), and shallower crypt depths in the duodenum than controls fed a normal diet (p < 0.05). Moreover, the major pro-inflammatory factors and antiviral proteins, as measured in the thymus and the spleen, were higher at 28 dph in ducks fed probiotics than those of 14 dph. After 28 d of feeding, the ducks were challenged with Escherichia coli (E. coli) and novel duck reovirus (NDRV), and ducks fed B. subtilis achieved survival rates of 43.3 and 100%, respectively, which were significantly greater than the control group's 20 and 83.3%. Altogether, diets with B. subtilis can improve Cherry Valley ducks' growth performance, innate immune response, and resistance against E. coli and NDRV.

Immune responses of ducks infected with duck Tembusu virus

Duck Tembusu virus (DTMUV) can cause serious disease in ducks, characterized by reduced egg production. Although the virus has been isolated and detection methods developed, the host immune responses to DTMUV infection are unclear. Therefore, we systematically examined the expression of immune-related genes and the viral distribution in DTMUV-infected ducks, using quantitative real-time PCR. Our results show that DTMUV replicates quickly in many tissues early in infection, with the highest viral titers in the spleen 1 day after infection. Rig-1, Mda5, and Tlr3 are involved in the host immune response to DTMUV, and the expression of proinflammatory cytokines (Il-1β, –2, –6, Cxcl8) and antiviral proteins (Mx, Oas, etc.) are also upregulated early in infection. The expression of Il-6 increased most significantly in the tissues tested. The upregulation of Mhc-I was observed in the brain and spleen, but the expression of Mhc-II was upregulated in the brain and downregulated in the spleen. The expression of the interferons was also upregulated to different degrees in the spleen but that of the brain was various. Our study suggests that DTMUV replicates rapidly in various tissues and that the host immune responses are activated early in infection. However, the overexpression of cytokines may damage the host. These results extend our understanding of the immune responses of ducks to DTMUV infection, and provide insight into the pathogenesis of DTMUV attributable to host factors.

Inhibition of reactive oxygen species production ameliorates inflammation induced by influenza A viruses via upregulation of SOCS1 and SOCS3

Highly pathogenic avian influenza virus infection is associated with severe mortality in both humans and poultry. The mechanisms of disease pathogenesis and immunity are poorly understood although recent evidence suggests that cytokine/chemokine dysregulation contributes to disease severity following H5N1 infection. Influenza A virus infection causes a rapid influx of inflammatory cells, resulting in increased reactive oxygen species production, cytokine expression, and acute lung injury. Proinflammatory stimuli are known to induce intracellular reactive oxygen species by activating NADPH oxidase activity. We therefore hypothesized that inhibition of this activity would restore host cytokine homeostasis following avian influenza virus infection. A panel of airway epithelial and immune cells from mammalian and avian species were infected with A/Puerto Rico/8/1934 H1N1 virus, low-pathogenicity avian influenza H5N3 virus (A/duck/Victoria/0305-2/2012), highly pathogenic avian influenza H5N1 virus (A/chicken/Vietnam/0008/2004), or low-pathogenicity avian influenza H7N9 virus (A/Anhui/1/2013). Quantitative real-time reverse transcriptase PCR showed that H5N1 and H7N9 viruses significantly stimulated cytokine (interleukin-6, beta interferon, CXCL10, and CCL5) production. Among the influenza-induced cytokines, CCL5 was identified as a potential marker for overactive immunity. Apocynin, a Nox2 inhibitor, inhibited influenza-induced cytokines and reactive oxygen species production, although viral replication was not significantly altered in vitro. Interestingly, apocynin treatment significantly increased influenza virus-induced mRNA and protein expression of SOCS1 and SOCS3, enhancing negative regulation of cytokine signaling. These findings suggest that apocynin or its derivatives (targeting host responses) could be used in combination with antiviral strategies (targeting viruses) as therapeutic agents to ameliorate disease severity in susceptible species.

IMPORTANCE

Highly pathogenic avian influenza virus infection causes severe morbidity and mortality in both humans and poultry. Wide-spread antiviral resistance necessitates the need for the development of additional novel therapeutic measures to modulate overactive host immune responses after infection. Disease severity following avian influenza virus infection can be attributed in part to hyperinduction of inflammatory mediators such as cytokines, chemokines, and reactive oxygen species. Our study shows that highly pathogenic avian influenza H5N1 virus and low-pathogenicity avian influenza H7N9 virus (both associated with human fatalities) promote inactivation of FoxO3 and downregulation of the TAM receptor tyrosine kinase, Tyro3, leading to augmentation of the inflammatory cytokine response. Inhibition of influenza-induced reactive oxygen species with apocynin activated FoxO3 and stimulated SOCS1 and SOCS3 proteins, restoring cytokine homeostasis. We conclude that modulation of host immune responses with antioxidant and/or anti-inflammatory agents in combination with antiviral therapy may have important therapeutic benefits.