Biological features of novel avian influenza A (H7N9) virus.

Human infection associated with a novel reassortant avian influenza H7N9 virus has recently been identified in China. A total of 132 confirmed cases and 39 deaths have been reported. Most patients presented with severe pneumonia and acute respiratory distress syndrome. Although the first epidemic has subsided, the presence of a natural reservoir and the disease severity highlight the need to evaluate its risk on human public health and to understand the possible pathogenesis mechanism. Here we show that the emerging H7N9 avian influenza virus poses a potentially high risk to humans. We discover that the H7N9 virus can bind to both avian-type (α2,3-linked sialic acid) and human-type (α2,6-linked sialic acid) receptors. It can invade epithelial cells in the human lower respiratory tract and type II pneumonocytes in alveoli, and replicated efficiently in ex vivo lung and trachea explant culture and several mammalian cell lines. In acute serum samples of H7N9-infected patients, increased levels of the chemokines and cytokines IP-10, MIG, MIP-1ß, MCP-1, IL-6, IL-8 and IFN-α were detected. We note that the human population is naive to the H7N9 virus, and current seasonal vaccination could not provide protection.

Indications that live poultry markets are a major source of human H5N1 influenza virus infection in China.

Human infections of H5N1 highly pathogenic avian influenza virus have continued to occur in China without corresponding outbreaks in poultry, and there is little conclusive evidence of the source of these infections. Seeking to identify the source of the human infections, we sequenced 31 H5N1 viruses isolated from humans in China (2005 to 2010). We found a number of viral genotypes, not all of which have similar known avian virus counterparts. Guided by patient questionnaire data, we also obtained environmental samples from live poultry markets and dwellings frequented by six individuals prior to disease onset (2008 and 2009). H5N1 viruses were isolated from 4 of the 6 live poultry markets sampled. In each case, the genetic sequences of the environmental and corresponding human isolates were highly similar, demonstrating a link between human infection and live poultry markets. Therefore, infection control measures in live poultry markets are likely to reduce human H5N1 infection in China.

Development and implementation of the quality control panel of RT-PCR and real-time RT-PCR for avian influenza A (H5N1) surveillance network in mainland China.

BACKGROUND: Reverse transcription PCR (RT-PCR) and real time RT-PCR (rRT-PCR) have been indispensable methods for influenza surveillance, especially for determination of avian influenza. The movement of testing beyond reference lab introduced the need of quality control, including the implementation of an evaluation system for validating personal training and sample proficiency testing. METHODS: We developed a panel with lysates of seasonal influenza virus (H1N1, H3N2 and B), serials of diluted H5N1 virus lysates, and in-vitro transcribed H5 hemaglutinin (HA) and an artificial gene RNAs for RT-PCR and rRT-PCR quality control assessment. The validations of stability and reproducibility were performed on the panel. Additionally, the panel was implemented to assess the detection capability of Chinese human avian influenza networks. RESULTS: The panel has relatively high stability and good reproducibility demonstrated by kappa's tests. In the implementation of panel on Chinese human avian influenza networks, the results suggested that there were a relatively low number of discrepancies for both concise and reproducibility in Chinese avian influenza virus net works. CONCLUSIONS: A quality control panel of RT-PCR and real-time RT-PCR for avian influenza A (H5N1) surveillance network was developed. An available statistical data, which are used to assess the detection capability of networks on avian influenza virus (H5N1), can be obtained relatively easily through implementation of the panel on networks.

Avian influenza A(H5N1) viruses can directly infect and replicate in human gut tissues.

The human respiratory tract is a major site of avian influenza A(H5N1) infection. However, many humans infected with H5N1 present with gastrointestinal tract symptoms, suggesting that this may also be a target for the virus. In this study, we demonstrated that the human gut expresses abundant avian H5N1 receptors, is readily infected ex vivo by the H5N1 virus, and produces infectious viral particles in organ culture. An autopsy colonic sample from an H5N1-infected patient showed evidence of viral antigen expression in the gut epithelium. Our results provide the first evidence, to our knowledge, that H5N1 can directly target human gut tissues.

Probable limited person-to-person transmission of highly pathogenic avian influenza A (H5N1) virus in China.

BACKGROUND: In December, 2007, a family cluster of two individuals infected with highly pathogenic avian influenza A (H5N1) virus was identified in Jiangsu Province, China. Field and laboratory investigations were implemented immediately by public-health authorities. METHODS: Epidemiological, clinical, and virological data were collected and analysed. Respiratory specimens from the patients were tested by reverse transcriptase (RT) PCR and by viral culture for the presence of H5N1 virus. Contacts of cases were monitored for symptoms of illness for 10 days. Any contacts who became ill had respiratory specimens collected for H5N1 testing by RT PCR. Sera were obtained from contacts for H5N1 serological testing by microneutralisation and horse red-blood-cell haemagglutinin inhibition assays. FINDINGS: The 24-year-old index case died, and the second case, his 52-year-old father, survived after receiving early antiviral treatment and post-vaccination plasma from a participant in an H5N1 vaccine trial. The index case's only plausible exposure to H5N1 virus was a poultry market visit 6 days before the onset of illness. The second case had substantial unprotected close exposure to his ill son. 91 contacts with close exposure to one or both cases without adequate protective equipment provided consent for serological investigation. Of these individuals, 78 (86%) received oseltamivir chemoprophylaxis and two had mild illness. Both ill contacts tested negative for H5N1 by RT PCR. All 91 close contacts tested negative for H5N1 antibodies. H5N1 viruses isolated from the two cases were genetically identical except for one non-synonymous nucleotide substitution. INTERPRETATION: Limited, non-sustained person-to-person transmission of H5N1 virus probably occurred in this family cluster.

[Clinical characteristic analysis of the first human case infected by influenza A (H5N1) in Jiangxi Province].

OBJECTIVE: To describe the clinical, laboratory and radiological presentation of a human case infected by influenza A (H5N1), and to understand its management and prognosis. METHODS: The clinical and autopsy data of the first human case infected by influenza A (H5N1) in Jiangxi Province were collected and analyzed. RESULTS: The first case infected by influenza A (H5N1) in Jiangxi Province was confirmed by laboratory findings with reverse transcription-polymerase chain reaction (RT-PCR) and influenza A (H5N1) isolation. The patient had been healthy in the past and exposed to the environment of bird flu before illness. The initial symptoms included high fever with influenza-like symptoms, and then cough and purulent sputum mixed with blood appeared. The clinical situation deteriorated progressively with occurrence of diarrhea and dyspnea. Laboratory abnormalities included decrease of peripheral white blood cells and lymphocytes, urine protein, dramatic increase of enzymes associated with hepatic injury and myocarditis and decrease of serum albumin. Six days later, penicillin-resistant streptococcus pneumoniae was isolated from multiple sputum cultures. With the deterioration of clinical situation, several other bacteria and fungi were found in sputum culture. Pulmonary infiltrates were evident in right middle and lower lobe at day 5 after illness, and rapidly progressed to involve bilateral lungs as acute respiratory distress syndrome (ARDS)-like changes. The patient was treated with antiviral, antibacterial, and antifungal reagents, and corticosteroids and invasive mechanical ventilation were also administered, but without any improvement. The patient died 27 days after the onset of symptoms and an autopsy was performed. Pathologically, the lungs exhibited diffuse alveolar damage. The lymphocytes in the spleen, the lymph nodes and the tonsils were depleted prominently with histiocytic hyperplasia and hemophagocytic phenomena. Edema and degeneration of myocytes in the heart and extensive acute tubular necrosis in the kidney were observed. CONCLUSION: The prognosis was very poor if influenza A (H5N1) infected human cases was developed as ARDS with multiple organ damage or failure.

Epidemiological and virological characteristics of pandemic influenza A (H1N1) school outbreaks in China in 2009.

BACKGROUND: During the 2009 pandemic influenza H1N1 (2009) virus (pH1N1) outbreak, school students were at an increased risk of infection by the pH1N1 virus. However, the estimation of the attack rate showed significant variability. METHODS: Two school outbreaks were investigated in this study. A questionnaire was designed to collect information by interview. Throat samples were collected from all the subjects in this study 6 times and sero samples 3 times to confirm the infection and to determine viral shedding. Data analysis was performed using the software STATA 9.0. FINDINGS: The attack rate of the pH1N1 outbreak was 58.3% for the primary school, and 52.9% for the middle school. The asymptomatic infection rates of the two schools were 35.8% and 37.6% respectively. Peak virus shedding occurred on the day of ARI symptoms onset, followed by a steady decrease over subsequent days (p = 0.026). No difference was found either in viral shedding or HI titer between the symptomatic and the asymptomatic infectious groups. CONCLUSIONS: School children were found to be at a high risk of infection by the novel virus. This may be because of a heightened risk of transmission owing to increased mixing at boarding school, or a lack of immunity owing to socio-economic status. We conclude that asymptomatically infectious cases may play an important role in transmission of the pH1N1 virus.

[The proliferation of H1N1 subtype influenza viruses in A549 and BEAS-2B cells].

OBJECTIVE: Analyze the proliferation of different host H1N1 subtype influenza viruses in A549 and BEAS-2B cells. METHODS: Human, avain and swine three hosts of the H1N1 influenza viruses infected A549 and BEAS-2B cells and analyze the characteristics of different periods after inocubation. Determine the receptor binding specificity of influenza virus by hemagglutination (HA) test with RBCs with two types of receptor. And the receptors on surfaces of A549 and BEAS-2B cells were tested by flow cytometry. RESULTS: The Cell Pathologic Effect (CPE) is obvious after 24 h inoculation in A549 cells by all the H1N1 influenza viruses, moreover, the peak hemagglutinin (HA) and 50% tissue culture cell infected dose (TCID50) titers was observed after 36 h of culturing in A549 cells. Otherwise, the CPE is not typical from 24 h-120 h inoculated by the same viruses and the HA, TCID50 titers were keep low all the periods in the BEAS-2B cell after inoculation. The receptor-binding preference of H1N1 viruses used in the study was screened by HA assay and some were found with 2-6-receptor binding affinity. Both SA a-2, 3Gal and SA a-2, 6Gal receptors were detected on A549 and BEAS-2B, furthermore, receptor density on A549 cells was significantly higher than that of BEAS-2B cells. CONCLUSION: A549 cells were susceptible to human, avian and swine H1N1 influenza viruses infection and permissively for viral replication. However, BEASE-2B cells with similar receptor pattern and epithelium-derived propriety as A549 cells were unsusceptible to their infection and replication. Possible host factors involved in effective viral infection and replication were needed further study.

The seroprevalence of pandemic influenza H1N1 (2009) virus in China.

BACKGROUND: Mainland China experienced pandemic influenza H1N1 (2009) virus (pH1N1) with peak activity during November-December 2009. To understand the geographic extent, risk factors, and attack rate of pH1N1 infection in China we conducted a nationwide serological survey to determine the prevalence of antibodies to pH1N1. METHODOLOGY/PRINCIPAL FINDINGS: Stored serum samples (n = 2,379) collected during 2006-2008 were used to estimate baseline serum reactogenicity to pH1N1. In January 2010, we used a multistage-stratified random sampling method to select 50,111 subjects who met eligibility criteria and collected serum samples and administered a standardized questionnaire. Antibody response to pH1N1 was measured using haemagglutination inhibition (HI) assay and the weighted seroprevalence was calculated using the Taylor series linearization method. Multivariable logistic regression analyses were used to examine risk factors for pH1N1 seropositivity. Baseline seroprevalence of pH1N1 antibody (HI titer ≥40) was 1.2%. The weighted seroprevalence of pH1N1 among the Chinese population was 21.5%(vaccinated: 62.0%; unvaccinated: 17.1%). Among unvaccinated participants, those aged 6-15 years (32.9%) and 16-24 years (30.3%) had higher seroprevalence compared with participants aged 25-59 years (10.7%) and ≥60 years (9.9%, P<0.0001). Children in kindergarten and students had higher odds of seropositivity than children in family care (OR: 1.36 and 2.05, respectively). We estimated that 207.7 million individuals (15.9%) experienced pH1N1 infection in China. CONCLUSIONS/SIGNIFICANCE: The Chinese population had low pre-existing immunity to pH1N1 and experienced a relatively high attack rate in 2009 of this virus. We recommend routine control measures such as vaccination to reduce transmission and spread of seasonal and pandemic influenza viruses.

[The study of multiple RT-PCR-based reverse dot blot hybridization technique for detecting influenza viruses].

OBJECTIVE: To establish a multiplex RT-PCR-based reverse dot blot hybridization technique to detect influenza viruses. METHODS: Obtain the HA nucleotide sequences of seasonal influenza H1N1, seasonal influenza H3N2, influenza H1N1 and human avian influenza H5N1 from GenBank. Design primers in conservative district and probes t in high variable region respectively, after analyzing the HA nucleotide sequences of influenza virus through the Vector NTI 9.0. Establish and optimize multiple RT-PCR system by comparing amplification efficiency and specificity at different primer concentrations. Establish the reverse dot hybridization system after optimizing the concentration of probes. To compare the sensitivity and specificity of this technique and the general RT-PCR Method through extracting the viral RNA of the mentioned influenza virus which are to be the reference substance. RESULTS: Successfully establish a multiplex RT-PCR-based reverse dot blot hybridization technique for detecting influenza viruses. This technique is 100-1000 times more sensitive than gel electrophoresis method, and it has a good specificity. CONCLUSION: Successfully established multiplex RT-PCR-based reverse dot blot hybridization technique for detecting influenza viruses.

[Expression and purification of avian influenza virus H5N1 NP protein, and screening interaction proteins of host cells in vitro].

OBJECTIVE: To express and purify H5N1 influenza virus (A/Anhui/1/2005) NP in prokaryotic system and to explore the NP-interacting proteins of human bronchial epithelial cells BEAS-2B in vitro. METHODS: The full length H5N1 NP gene fragment was amplified by PCR, inserted into prokaryotic expression vector (pET30a) to generate NP expression plasmid pET30a-NP. After transforming pET30a-NP into E. coli (BL21), the expression of soluble NP protein was induced by IPTG. The expressed NP protein was purified by two steps with metal chelation chromatography and ion exchange chromatography. Then the total proteins of BEAS-2B cells was extracted for screening the components which have protein-protein interaction with purified NP by pull-down and LC-MS/MS methods. RESULTS: The expression of H5N1 NP protein could be induced by IPTG in bacterial system using expression plasmid pET30a-NP. The soluble NP was purified. Twenty proteins were found by pull-down and LC-MS/MS, the further experiments may be needed to prove protein-protein interaction between them. CONCLUSION: The soluble H5N1 NP fusion protein with high purity was obtained and twenty proteins were found which could interact with it by pull-down and LC-MS/MS.

A systematic molecular pathology study of a laboratory confirmed H5N1 human case.

Autopsy studies have shown that human highly pathogenic avian influenza virus (H5N1) can infect multiple human organs other than just the lungs, and that possible causes of organ damage are either viral replication and/or dysregulation of cytokines and chemokines. Uncertainty still exists, partly because of the limited number of cases analysed. In this study, a full autopsy including 5 organ systems was conducted on a confirmed H5N1 human fatal case (male, 42 years old) within 18 hours of death. In addition to the respiratory system (lungs, bronchus and trachea), virus was isolated from cerebral cortex, cerebral medullary substance, cerebellum, brain stem, hippocampus ileum, colon, rectum, ureter, aortopulmonary vessel and lymph-node. Real time RT-PCR evidence showed that matrix and hemagglutinin genes were positive in liver and spleen in addition to positive tissues with virus isolation. Immunohistochemistry and in-situ hybridization stains showed accordant evidence of viral infection with real time RT-PCR except bronchus. Quantitative RT-PCR suggested that a high viral load was associated with increased host responses, though the viral load was significantly different in various organs. Cells of the immunologic system could also be a target for virus infection. Overall, the pathogenesis of HPAI H5N1 virus was associated both with virus replication and with immunopathologic lesions. In addition, immune cells cannot be excluded from playing a role in dissemination of the virus in vivo.

A comprehensive surveillance of adamantane resistance among human influenza A virus isolated from mainland China between 1956 and 2009.

BACKGROUND: Adamantane-derived drugs have been used for treatment and prophylaxis of influenza A virus infection for many years worldwide. Rapid surveillance of antiviral drug resistance is important for appropriate clinical guideline development. Here, we retrospectively assessed adamantane resistance among different influenza A subtypes (H1N1, H3N2 and H5N1) over 53 years (1956-2009) in mainland China. METHODS: A total of 1,451 viruses, including 773 H3N2 viruses, 647 H1N1 viruses and 31 human H5N1 viruses, were analysed by matrix gene sequencing and assayed for drug resistance. RESULTS: Our results show that the prevalence of adamantane-resistant H3N2 viruses was low between 1956 and 2002, but substantially increased in 2003 to the extent that since 2006 all H3N2 viruses have been drug resistant. The percentage of adamantane-resistant H1N1 viruses also increased from 50.0% in 2004 to 98.7% in 2007; however, this decreased to 46.7% in 2009. Only three adamantane-resistant H5N1 viruses have been detected since 2003, when the first case of human H5N1 virus infection was detected in mainland China. Phylogenetic analysis demonstrated that the increase of adamantane-resistant isolates was caused by point mutations or intrasubtype reassortment instead of intersubtype reassortment. CONCLUSIONS: Because of the high percentage of adamantane-resistant H3N2 and H1N1 viruses in mainland China, the use of amantadine and rimantadine drugs for prophylaxis and treatment of current seasonal influenza A infection is not recommended.

Visual detection of pandemic influenza A H1N1 Virus 2009 by reverse-transcription loop-mediated isothermal amplification with hydroxynaphthol blue dye.

A sensitive reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for rapid visual detection of pandemic influenza A H1N1 virus infection. The reaction was performed in one step in a single tube at 65 degrees C for 60 min with the addition of hydroxynaphthol blue (HNB) dye prior to amplification. The detection limit of the RT-LAMP assay was approximately 60 copies, and no cross-detection was observed. The assay was evaluated further with 50 clinical specimens diagnosed clinically with seasonal influenza or pandemic influenza A H1N1 virus infection. RT-LAMP with HNB dye was demonstrated to be a sensitive and easy assay for rapid detection of pandemic influenza A H1N1 virus.

[Characterization of pseudotyped viruses coated with hemagglutinin of H5N1 avian influenza].

OBJECTIVE: To construct pseudovirus bearing H5N1 HA based on a lentivirus vector system. Then we study the biological feature of the pseudovirus. With the newly established viral particles, we performed the serological tests. METHODS: H5N1 avian influenza virus that isolated from human case was cloned to construct pLP-HA, then pLP-HA co-transfected with lentivirus vector plasmids pLP1, pLP2 and pEmGFP into 293T cells. The supernatant was harvested 48h post-transfection. Concentrated by super centrifuge, the pseudotyped viruses were analyzed by infection test, HA test and micro-neutralization test. At the same time, optimized HA gene and a Vietnam H5N1 HA gene were used to construct pseudotyped virus for comparison. RESULTS: Pseudotyped virus particles can be observed with electronic microscope. Western-blot revealed that HA glycoprotein can be expressed in the virions. Our neutralization assay by using the pseudoviruses was comparable with the conventional microneutralization assay with wild-type viruses. A high degree of correlation was detected. CONCLUSION: Pseudotyped Viruses coated with HA of H5N1 High Pathogenic Avian Influenza were successfully constructed; it can be used to for the microneutralization assay. The HA gene from different sources affect the efficiency of the packaging of the pseudovirus. But the optimized HA gene can not obviously improve packaging efficiency of the pseudovirus.

[Construction and characterization of reverse genetic system for H9N2 avian influenza].

OBJECTIVE: To provide a technology platform for vaccine development as well as the research on transmission and pathogenesis, the reverse genetic system for H9N2 avian influenza virus was established. METHODS: Eight full-length cDNAs of avian influenza virus A/Guangzhou/333/99 (H9N2) were amplified by RT-PCR and separately cloned into the transcription/expression vector, pCI-polI. The 8 plasmids DNA was cotransfected into 293T cell, the cell supernatant was collected and inoculated into embryonated eggs, the rescued virus from the allantoic fluid was identified by hemagglutinination assay. RESULTS: The avian influenza H9N2 virus was successfully rescued by 8 plasmids co-transfection in 293T cells. The hemagglutinination titer of the rescued virus is up to 2(9)/50 microl and its growth curve remained relatively as to the wild-type virus. CONCLUSION: The reverse genetic for avian influenza H9N2 subtype virus has been established successfully.

[The virus isolation analysis of the H5N1 subtype human avain influenza cases in mainland China from 2005 to 2009].

OBJECTIVE: To analyse the correlation between the virus isolation and the specimen collection of the H5N1 human high pathogenic avain influenza cases in Mainland China. METHODS: The specimens were collected in Mainland China from 2005.10 to 2009.3 and the H5N1 viruses were isolated by passage in embryonated chicken eggs. RESULTS: Most specimens were obtained within 14 days after disease onset. For the specimens collected within 7 days, the isolation rate was relatively high and the difference of the positive rate between different years was lower than those specimens collected after 7 days. Most of the samples in our study were collected from the upper or lower respiratory tract with few from blood, feces, et al. The isolation rate of lower respiratory specimens was higher and the difference of the positive rate between different years was relatively lower than those from upper respiratory specimens. CONCLUSION: We suggest that the samples should be collected from lower respiratory tract during the acute phase to get the higher isolation rate.

[Establishment of a method for rapid detection of the nucleic acid of the novel A (H1N1) influenza virus].

A new flu caused by a novel influenza A(H1N1) virus has spread over the United States, Mexico and more than 40 other countries. And because of the immediate global concern, WHO has announced that the current level of influenza pandemic alert is raised to phase 5, indicating approaching of an influenza pandemic. As patients suffering from the influenza A (H1N1) have the similar symptoms as patients with seasonal influenza, differential detection and identification of the influenza virus have to depend on specific laboratory tests. We have successfully developed a RT-PCR based method for detection of the influenza A (H1N1) virus, and had applied the method to detection of clinical samples.

[Laboratory confirmation of the first influenza A (H1N1) imported case in Mainland China].

The clinical throat swab specimen of an imported suspected case of influenza A (H1N1) was detec ted with real-time PCR, RT-PCR and subsequently confirmed by gene sequencing. The presence of influ enza A (H1N1) virus confirmed the first case with A (H1N1) infection in Mainland China.

[Detection of influenza viruses/avian influenza viruses and identification of virulence using a microarray].

OBJECTIVE: To establish the DNA microarray to detect influenza viruses and avian influenza viruses, and identify their virulence. METHODS: Hemagglutinin (HA), neuramidinase (NA) and nucleoprotein(NP) genes were chosen simultaneously as targets for designing a microarray used for detection of viruses and identification virulence. The nucleic acid were amplified by single primer amplication (SPA). And then its specificity,sensitivity and reproducibility were evaluated. RESULTS: The microarray was able to specially detect H1N1, H3N2, B influenza viruses and H5N1, H9N2 avian influenza viruses. Their limits were 8HAU, 16HAU, 32HAU, and 8HAU, 8HAU respectively. The limit for virulence was 32HAU. When samples were analyzed by both RT-PCR and microarray in parallel, the results agreed in 83.9% (47/56). CONCLUSION: The microarray can detect and distinguish five tested viruses, and especially identify virulence. It not only supplies an assistant tool for clinical diagnosis and control of infectious disease, but also is valuable for controlling and preventing outbreak of avian influenza epidemic.