Yasushi Suzuki

Niigata University, Niahi-niigata, Niigata, Japan

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Publications (28)92.26 Total impact

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    ABSTRACT: Coughing plays an important role in influenza transmission; however, there is insufficient information regarding the viral load in cough because of the lack of convenient and reliable collection methods. We developed a portable airborne particle-collection system to measure the viral load; it is equipped with an air sampler to draw air and pass it through a gelatin membrane filter connected to a cone-shaped, megaphone-like device to guide the cough airflow to the membrane. The membrane was dissolved in a medium, and the viral load was measured using quantitative real-time reverse transcriptase-polymerase chain reaction and a plaque assay. The approximate viral recovery rate of this system was 10% in simulation experiments to collect and quantify the viral particles aerosolized by a nebulizer. Using this system, cough samples were collected from 56 influenza A patients. The total viral detection rate was 41% (23/56), and the viral loads varied significantly (from <10, less than the detection limit, to 2240 viral gene copies/cough). Viable viruses were detected from 3 samples with ≤18 plaque forming units per cough sample. The virus detection rates were similar among different groups of patients infected with different viral subtypes and during different influenza seasons. Among patients who did not receive antiviral treatment, viruses were detected in one of six cases in the vaccinated group and four of six cases in the unvaccinated group. We found cases with high viral titers in throat swabs or oral secretions but very low or undetectable in coughs and vice versa suggesting other possible anatomical sites where the viruses might be mixed into the cough. Our system is easy to operate, appropriate for bedside use, and is useful for comparing the viral load in cough samples from influenza patients under various conditions and settings. However, further large-scale studies are warranted to validate our results.
    PLoS ONE 01/2014; 9(8):e103560. · 3.53 Impact Factor
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    ABSTRACT: Two new influenza virus neuraminidase inhibitors (NAIs), peramivir and laninamivir, were approved in 2010 which resulted to four NAIs that were used during the 2010-2011 influenza season in Japan. This study aims to monitor the susceptibility of influenza virus isolates in 2009-2010 and 2010-2011 influenza seasons in Japan to the four NAIs using the fluorescence-based 50% inhibitory concentration (IC50) method. Outliers were identified using box-and-whisker plot analysis and full NA gene sequencing was performed to determine the mutations that are associated with reduction of susceptibility to NAIs. A total of 117 influenza A(H1N1)pdm09, 59 A(H3N2), and 18 type B viruses were tested before NAI treatment and eight A(H1N1)pdm09 and 1 type B viruses were examined from patients after NAI treatment in the two seasons. NA inhibition assay showed type A influenza viruses were more susceptible to NAIs than type B viruses. The peramivir and laninamivir IC50 values of both type A and B viruses were significantly lower than the oseltamivir and zanamivir IC50 values. Among influenza A(H1N1)pdm09 viruses, the prevalence of H274Y viruses increased from 0% in the 2009-2010 season to 3% in the 2010-2011 season. These H274Y viruses were resistant to oseltamivir and peramivir with 200-300 fold increase in IC50 values but remained sensitive to zanamivir and laninamivir. Other mutations in NA, such as I222T and M241I were identified among the outliers. Among influenza A(H3N2) viruses, two outliers were identified with D151G and T148I mutations, which exhibited a reduction in susceptibility to oseltamivir and zanamivir, respectively. Among type B viruses, no outliers were identified to the four NAIs. For paired samples that were collected before and after drug treatment, three (3/11; 27.3%) H274Y viruses were identified among A(H1N1)pdm09 viruses after oseltamivir treatment but no outliers were found in the laninamivir-treatment group (n=3). Despite widespread use of NAIs in Japan, the prevalence of NAI-resistant influenza viruses is still low.
    Antiviral research 06/2013; · 3.61 Impact Factor
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    ABSTRACT: Background Pandemic influenza A(H1N1) 2009 virus was first detected in Japan in May 2009 and continued to circulate in the 2010–2011 season. This study aims to characterize human influenza viruses circulating in Japan in the pandemic and post-pandemic periods and to determine the prevalence of antiviral-resistant viruses. Methods Respiratory specimens were collected from patients with influenza-like illness on their first visit at outpatient clinics during the 2009–2010 and 2010–2011 influenza seasons. Cycling probe real-time PCR assays were performed to screen for antiviral-resistant strains. Sequencing and phylogenetic analysis of the HA and NA genes were done to characterize circulating strains. Results and Conclusion In the pandemic period (2009–2010), the pandemic influenza A(H1N1) 2009 virus was the only circulating strain isolated. None of the 601 A(H1N1)pdm09 virus isolates had the H275Y substitution in NA (oseltamivir resistance) while 599/601 isolates (99.7%) had the S31N substitution in M2 (amantadine resistance). In the post-pandemic period (2010–2011), cocirculation of different types and subtypes of influenza viruses was observed. Of the 1,278 samples analyzed, 414 (42.6%) were A(H1N1)pdm09, 525 (54.0%) were A(H3N2) and 33 (3.4%) were type-B viruses. Among A(H1N1)pdm09 isolates, 2 (0.5%) were oseltamivir-resistant and all were amantadine-resistant. Among A(H3N2) viruses, 520 (99.0%) were amantadine-resistant. Sequence and phylogenetic analyses of A(H1N1)pdm09 viruses from the post-pandemic period showed further evolution from the pandemic period viruses. For viruses that circulated in 2010–2011, strain predominance varied among prefectures. In Hokkaido, Niigata, Gunma and Nagasaki, A(H3N2) viruses (A/Perth/16/2009-like) were predominant whereas, in Kyoto, Hyogo and Osaka, A(H1N1)pdm09 viruses (A/New_York/10/2009-like) were predominant. Influenza B Victoria(HA)-Yamagata(NA) reassortant viruses (B/Brisbane/60/2008-like) were predominant while a small proportion was in Yamagata lineage. Genetic variants with mutations at antigenic sites were identified in A(H1N1)pdm09, A(H3N2) and type-B viruses in the 2010–2011 season but did not show a change in antigenicity when compared with respective vaccine strains.
    PLoS ONE 06/2012; 7(6). · 3.53 Impact Factor
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    ABSTRACT: The clinical effectiveness of the newly released neuraminidase inhibitors (NAIs) laninamivir and peramivir has not been sufficiently evaluated in influenza-infected patients in clinical and practical settings. In this study, we analyzed the clinical data of 211 patients infected with influenza A virus subtype H3N2 (A(H3N2)) and 45 patients infected with influenza A virus subtype H1N1pdm (A(H1N1)pdm09) who received the NAIs oseltamivir, zanamivir, laninamivir, or peramivir during the 2010-2011 influenza season. The duration of fever from the first dose of the NAI to fever alleviation to <37.5 °C was evaluated as an indicator of the clinical effectiveness of the NAIs in the influenza-infected patients. For the A(H3N2)-infected patients, Kaplan-Meier analysis showed the peramivir treatment group had the fastest time of fever alleviation to <37.5 °C (median 17.0 h, 95 % confidence interval [CI] 7.2-26.8 h) of the four treatment groups. No significant difference was found in the time to fever alleviation among the other antivirals, oseltamivir, zanamivir, and laninamivir. Results of multivariate analysis, using a Cox proportional-hazards model (hazard ratio 3.321) adjusted for the factors age, sex, body weight, vaccination status, time from onset to the clinic visit, and body temperature showed significantly faster fever alleviation in the peramivir treatment group compared with the oseltamivir treatment group. For the A(H1N1)pdm09-infected patients, only the oseltamivir and zanamivir treatment groups were compared, and no significant difference in time to alleviation of fever was observed between the two groups. Based on a cycling probe real-time polymerase chain reaction (PCR) assay, none of the A(H1N1)pdm09 strains in this study had the H275Y mutation conferring oseltamivir resistance. Further evaluation of the clinical effectiveness of the newly released NAIs for influenza-infected patients, including those infected with A(H1N1)pdm09, is needed.
    Journal of Infection and Chemotherapy 05/2012; · 1.55 Impact Factor
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    ABSTRACT: In June 2009, the World Health Organization announced the 21st century's first influenza pandemic caused by pandemic influenza H1N1 2009 (H1N1 pdm). Our goal was to analyze antiviral drug resistance and the phylogenetic relationships among hemagglutinin (HA) and neuraminidase (NA) genes of H1N1 pdm samples in Lebanon. Nasopharyngeal swabs were collected from 197 patients with influenza-like illness from May 2009 through January 2010. Of the 50 influenza A-positive samples, 30 were analyzed for antiviral drug resistance by using in vitro susceptibility assays and cycling-probe real-time PCR. The HA and NA genes were also analyzed. The results of hemagglutination-inhibition assays confirmed that all 30 analyzed samples were H1N1 pdm. In July 2009, community transmission of H1N1 pdm was detected in Lebanon, and an outbreak occurred in October 2009. The outbreak cases were caused by a strain with 4 mutations in the NA gene (i.e., V42I, N68T, N248D, and E462K) and 2 mutations in the HA gene: 1 in the Ca1 antigenic site (i.e., S206T) and 1 in the Ca2 antigenic site (i.e., D225E). This strain was closely related to a major H1N1 pdm cluster that was isolated worldwide. All 30 samples were amantadine-resistant, and none were zanamivir-resistant. The 1 oseltamivir-resistant sample appeared to be from a community-transmitted case in an otherwise healthy 2-year-old child. Continuous monitoring of oseltamivir susceptibility among H1N1 pdm is essential to guide the effective use of this drug.
    Journal of clinical virology: the official publication of the Pan American Society for Clinical Virology 07/2011; 51(3):170-4. · 3.12 Impact Factor
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    ABSTRACT: The objective of this study was to characterize the off-seasonal influenza virus A subtype H3N2, which caused an outbreak in an elderly hospital in Niigata, Japan. Virus isolates were subtyped by the hemagglutination-inhibition test and screened for antiviral drug sensitivity by real-time PCR using cycling probe technology the and 50% inhibitory concentration (IC(50)) method. Whole genome sequencing was performed in order to determine the phylogeny of the outbreak virus. Seven virus isolates were analyzed in this study, and the results showed that all belonged to the influenza virus A (H3N2). These viruses exhibited the S31N mutation in M2, which confers resistance to amantadine. The results of the IC(50) analysis showed that these viruses were sensitive to both oseltamivir and zanamivir. Whole genome analysis revealed that the virus was similar to the A/Perth/16/2009 strain and that it is a triple reassortant virus with a 3+3+2 pattern of segment recombination.
    Japanese journal of infectious diseases. 05/2011; 64(3):237-41.
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    ABSTRACT: To describe outbreaks of nosocomial influenza infection with molecular methods and to elucidate the viral linkages among outbreak case patients including both inpatients and healthcare workers (HCWs). A 180-bed acute and long-term care hospital in Japan. Retrospective observational study of nosocomial outbreaks of infection with influenza A/H3N2. Together with information about onset dates and vaccination history, we obtained nasopharyngeal swab samples from individuals with cases of influenza or influenza-like illness (ILI). The hemagglutinin genes of the recovered viruses were sequenced and compared, along with those of community-circulating strains, for similarity by phylogenetic tree analysis. The outbreaks occurred from February 26 through April 3, 2007, during the 2006-2007 epidemic season, and they involved 11 patients and 13 HCWs. The 2 outbreaks involved 2 different genotypes of influenza A/H3N2 viruses. These virus variants were closely related to the influenza strains that were circulating in the community during the same epidemic season. This study showed the dissemination of highly homologous influenza virus variants among inpatients and HCWs within a short period, as a result of nosocomial transmission. These strains were also similar to influenza strains that were circulating in the community.
    Infection Control and Hospital Epidemiology 03/2011; 32(3):267-75. · 4.02 Impact Factor
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    ABSTRACT: In eight successive seasons (2001 to 2009), a total of 726 human respiratory syncytial virus (HRSV) infections from a total of 1,560 children with acute lower respiratory tract illness were identified. Molecular analysis of the attachment (G) protein gene confirmed that 52 (7.8%) children were infected more than once with any of the 3 genotypes of HRSV-A (genotypes GA5, NA1, and NA2) and/or 6 genotypes of HRSV-B (genotypes BA4, BA5, and BA7 to BA10). Repeated infections in 46 cases (82.1%) occurred in the next season, and only one case occurred in the same season (10-day interval). First infections were 33 (63.5%) HRSV-A cases and 19 (36.5%) HRSV-B cases, whereas second infections occurred in 35 (67.3%) HRSV-A cases and 17 (32.7%) HRSV-B cases. Third infections were attributed to 4 (100.0%) HRSV-A cases. Homologous subgroup reinfections were detected in 28 cases, 23 HRSV-A cases and 5 HRSV-B cases (P = 0.005), whereas homologous genotype reinfections were detected only for 5 HRSV-A cases (2GA5 and 3NA2) but not any HRSV-B case. Heterologous subgroup reinfections were detected in 28 cases, 12 cases from HRSV-A-to-HRSV-B reinfections and 16 cases from HRSV-B-to-HRSV-A reinfections. Genotypes NA1 and NA2 had higher numbers of heterologous genotype infections than did other genotypes. Our observations suggest that repeated infections occur more frequently in HRSV-A strains than in HRSV-B strains, and heterologous genotype reinfections occur more frequently than homologous genotype reinfections, especially in the case of the emerging genotypes NA1 and NA2 of HRSV-A strains that circulated in the community during our study period.
    Journal of clinical microbiology 12/2010; 49(3):1034-40. · 4.16 Impact Factor
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    ABSTRACT: Neuraminidase inhibitors are agents used against influenza viruses; however, the emergence of drug-resistant strains is a major concern. Recently, the prevalence of oseltamivir-resistant seasonal influenza A (H1N1) virus increased globally and the emergence of oseltamivir-resistant pandemic influenza A (H1N1) 2009 viruses was reported. In this study, we developed a cycling probe real-time PCR method for the detection of oseltamivir-resistant seasonal influenza A (H1N1) and pandemic influenza A (H1N1) 2009 viruses. We designed two sets of primers and probes that were labeled with 6-carboxyfluorescein or 6-carboxy-X-rhodamine to identify single nucleotide polymorphisms (SNPs) that correspond to a histidine and a tyrosine at position 275 in the neuraminidase protein, respectively. These SNPs confer susceptibility and resistance to oseltamivir, respectively. In the 2007-2008 season, the prevalence of oseltamivir-resistant H1N1 viruses was 0% (0/72), but in the 2008-2009 season, it increased to 100% (282/282). In the 2009-2010 season, all of the pandemic influenza A (H1N1) 2009 viruses were susceptible to oseltamivir (0/73, 0%). This method is sensitive and specific for the screening of oseltamivir-resistant influenza A (H1N1) viruses. This method is applicable to routine laboratory-based monitoring of drug resistance and patient management during antiviral therapy.
    Journal of clinical microbiology 11/2010; 49(1):125-30. · 4.16 Impact Factor
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    ABSTRACT: Phylogenetic analysis of respiratory syncytial virus (RSV) group B genotype BA strains from the 2002-2003 to 2009-2010 seasons collected in Niigata, Japan, revealed four distinct clusters, designated new BA genotypes BA7, BA8, BA9, and BA10. These new genotypes were not associated with large outbreaks in the community.
    Journal of clinical microbiology 09/2010; 48(9):3423-7. · 4.16 Impact Factor
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    ABSTRACT: The emergence of antiviral drug-resistant strains of the influenza virus in addition to the rapid spread of the recent pandemic A(H1N1) 2009 virus highlight the importance of surveillance of influenza in identifying new variants as they appear. In this study, genetic characteristics and antiviral susceptibility patterns of influenza samples collected in Lebanon during the 2008-09 season were investigated. Forty influenza virus samples were isolated from 89 nasopharyngeal swabs obtained from patients with influenza-like illness. Of these samples, 33 (82.5%) were A(H3N2), 3 (7.5%) were A(H1N1), and 4 (10%) were B. All the H3N2 viruses were resistant to amantadine but were sensitive to oseltamivir and zanamivir; while all the H1N1 viruses were resistant to oseltamivir (possessed H275Y mutation, N1 numbering, in their NA) but were sensitive to amantadine and zanamivir. In the case of influenza B, both Victoria and Yamagata lineages were identified (three and one isolates each, respectively) and they showed decreased susceptibility to oseltamivir and zanamivir when compared to influenza A viruses. Influenza circulation patterns in Lebanon were very similar to those in Europe during the same season. Continued surveillance is important to fully elucidate influenza patterns in Lebanon and the Middle East in general, especially in light of the current influenza pandemic.
    Journal of Medical Virology 07/2010; 82(7):1224-8. · 2.37 Impact Factor
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    ABSTRACT: Little is known about whether neuraminidase inhibitors are effective for children infected with oseltamivir-resistant influenza A(H1N1) viruses. Children aged 15 years and younger having influenza-like illness and who visited outpatient clinics within 48 hours of fever onset were enrolled from 2006-2007 to 2008-2009 influenza seasons in Japan. Patients received oseltamivir, zanamivir, or no treatment after screening by a rapid antigen test. Nasopharyngeal swabs were collected before antiviral therapy and were used for virus isolation. Oseltamivir resistance was determined by detection of the H275Y mutation in neuraminidase, and susceptibility test using neuraminidase inhibition assay. Daily body temperature was evaluated according to drug type and susceptibility by univariate and multivariate analyses. Of 1647 patients screened, 238 oseltamivir-resistant H1N1 cases (87 oseltamivir-treated, 64 zanamivir-treated, and 87 nontreated) and 110 oseltamivir-susceptible cases (60 oseltamivir-treated and 50 nontreated) were evaluated. In oseltamivir-resistant cases, fever on days 4 to 5 after the start of treatment was significantly higher in oseltamivir-treated and nontreated than in zanamivir-treated patients (P < 0.05). In oseltamivir-susceptible cases, fever was significantly lower in oseltamivir-treated than nontreated on days 3 to 6 (P < 0.01). Similar findings were obtained for duration of the fever and proportion of recurrent fever. Reduced effectiveness of oseltamivir was more prominent in children 0 to 6 years old than in those 7 to 15 years old. Multiple logistic regression analysis showed that lower age, nontreatment, and oseltamivir treatment of oseltamivir-resistant patients were factors associated with the duration of the longer fever. Infection with oseltamivir-resistant viruses significantly reduced the effectiveness of oseltamivir, and this tendency was more apparent in younger children.
    The Pediatric Infectious Disease Journal 05/2010; 29(10):898-904. · 3.57 Impact Factor
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    ABSTRACT: The emergence and widespread occurrence of antiviral drug-resistant seasonal human influenza A viruses, especially oseltamivir-resistant A/H1N1 virus, are major concerns. To understand the genetic background of antiviral drug-resistant A/H1N1 viruses, we performed full genome sequencing of prepandemic A/H1N1 strains. Seasonal influenza A/H1N1 viruses, including antiviral-susceptible viruses, amantadine-resistant viruses, and oseltamivir-resistant viruses, obtained from several areas in Japan during the 2007-2008 and 2008-2009 influenza seasons were analyzed. Sequencing of the full genomes of these viruses was performed, and the phylogenetic relationships among the sequences of each individual genome segment were inferred. Reference genome sequences from the Influenza Virus Resource database were included to determine the closest ancestor for each segment. Phylogenetic analysis revealed that the oseltamivir-resistant strain evolved from a reassortant oseltamivir-susceptible strain (clade 2B) which circulated in the 2007-2008 season by acquiring the H275Y resistance-conferring mutation in the NA gene. The oseltamivir-resistant lineage (corresponding to the Northern European resistant lineage) represented 100% of the H1N1 isolates from the 2008-2009 season and further acquired at least one mutation in each of the polymerase basic protein 2 (PB2), polymerase basic protein 1 (PB1), hemagglutinin (HA), and neuraminidase (NA) genes. Therefore, a reassortment event involving two distinct oseltamivir-susceptible lineages, followed by the H275Y substitution in the NA gene and other mutations elsewhere in the genome, contributed to the emergence of the oseltamivir-resistant lineage. In contrast, amantadine-resistant viruses from the 2007-2008 season distinctly clustered in clade 2C and were characterized by extensive amino acid substitutions across their genomes, suggesting that a fitness gap among its genetic components might have driven these mutations to maintain it in the population.
    Journal of clinical microbiology 04/2010; 48(4):1085-92. · 4.16 Impact Factor
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    ABSTRACT: In 2007 and 2008 in Myanmar, we detected influenza viruses A (H3N2) that exhibited reduced sensitivity to both zanamivir and amantadine. These rare and naturally occurring viruses harbored a novel Q136K mutation in neuraminidase and S31N mutation in M2.
    Emerging Infectious Diseases 03/2010; 16(3):493-6. · 6.79 Impact Factor
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    ABSTRACT: The prevalence of amantadine-resistant influenza A/H3N2 viruses (belonging to the N-lineage), possessing an S31N mutation in the M2 protein and S193F and D225N substitutions in their HA1 subunit, has significantly increased worldwide since 2005. The aim of this study was to clarify the genomic events contributing to the evolution and continuity of the N-lineage amantadine-resistant viruses. The full genome sequence of A/H3N2 isolates, including both amantadine-resistant and amantadine-sensitive viruses, collected in Japan between 2006 and 2008, was determined and phylogenetically compared with isolates obtained from the database. On the basis of the full genome sequence analysis, the N-lineage could be further divided into three genetically related clades: N1 (A/Wisconsin/67/2005-like amantadine-resistant viruses from years 2005-2007), N2 (amantadine-sensitive viruses from 2007) and N3 (A/Brisbane/10/2007-like amantadine-resistant viruses from 2007 and 2008). The 2006/2007 season showed cocirculation of antigenic variants of amantadine-resistant viruses of clades N1 and N3 in addition to the N2-sensitive viruses. In the 2007/2008 season, the clade N3 amantadine-resistant lineage dominated and replaced other strains. Phylogenetic analysis of each individual segment suggested that N2 and N3 were generated from two independent reassortment events involving clade N1 viruses and pre-N-lineage strains. Our data show that several reassortment events have contributed to the evolution of amantadine-resistant A/H3N2 strains and, consequently, to the successful spread of this lineage. Although amantadine resistance is caused by single amino acid mutations in the M2 protein, genome-wide adjustment involving multiple genes appears to be necessary to obtain efficient replication and transmission of resistant viruses. Such adjustments are attainable through reassortment of segments among different virus lineages.
    Antiviral therapy 01/2010; 15(3):307-19. · 3.07 Impact Factor
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    ABSTRACT: A substantial increase in oseltamivir-resistant A(H1N1) influenza viruses was reported in Europe in late 2007. To monitor the antiviral susceptibility profile of human A(H1N1) influenza viruses in Japan during the 2007-2008 and 2008-2009 seasons. Viruses were obtained from respiratory samples of patients with influenza collected in Japan between December 2007 and April 2008 (n=1046) and between December 2008 and April 2009 (n=1789). Oseltamivir resistance was determined by an H274Y-specific real-time PCR cycling probe assay and a neuraminidase inhibition assay. Amantadine resistance was assessed by sequencing the M2 gene. Sequencing of the hemagglutinin and NA genes was performed to infer phylogenetic relationships between different strains. Three of 687 (0.4%) A(H1N1) viruses from the 2007-2008 season and 745 of 745 (100%) viruses from the 2008-2009 season carried the NA-H274Y substitution and demonstrated a >300-fold reduction in oseltamivir susceptibility. All oseltamivir-resistant viruses from the 2008-2009 season possessed an A193T substitution in the receptor-binding domain of the hemagglutinin. Amantadine resistance was detected in 431 of 687 (62.7%) and 0 of 745 (0.0%) of the A(H1N1) viruses from the 2007-2008 and 2008-2009 seasons, respectively. A dramatic surge in oseltamivir-resistant A(H1N1) viruses possessing the NA-H274Y substitution was detected in Japan during the 2008-2009 season. The emergence of oseltamivir-resistant viruses was facilitated by mutations in the viral genome. Intensified surveillance, including phenotypic assays and sequencing of the hemagglutinin, neuraminidase, and M2 gene would allow monitoring of the spread and evolution of drug-resistant influenza virus variants.
    Journal of clinical virology: the official publication of the Pan American Society for Clinical Virology 12/2009; 47(1):23-8. · 3.12 Impact Factor
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    ABSTRACT: Amantadine is one of the antiviral agents used to treat influenza A virus infections, but resistant strains have widely emerged worldwide. In the present study, we developed a novel method to detect amantadine-resistant strains harboring the Ser31Asn mutation in the M2 gene based on the cycling probe method and real-time PCR. We also studied the rate of amantadine resistance in the 2007-2008 influenza season in Japan. Two different primer and cycling probe sets were designed for A/H1N1 and A/H3N2 each to detect a single nucleotide polymorphism corresponding to Ser/Asn at residue 31 of the M2 protein. By using nasopharyngeal swabs from patients with influenza-like and other respiratory illnesses and virus isolates, the specificity and the sensitivity of the cycling probe method were evaluated. High frequencies of amantadine resistance were detected among the A/H1N1 (411/663, 62%) and A/H3N2 (56/56, 100%) virus isolates collected from six prefectures in Japan in the 2007-2008 influenza season. We confirmed that the cycling probe method is suitable for the screening of both nasopharyngeal swabs and influenza virus isolates for amantadine-resistant strains and showed that the incidence of amantadine resistance among both A/H1N1 and A/H3N2 viruses remained high in Japan during the 2007-2008 season.
    Journal of clinical microbiology 11/2009; 48(1):57-63. · 4.16 Impact Factor
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    ABSTRACT: To perform genetic analysis of influenza A and B viruses in Myanmar from 2005 to 2007 and to determine the prevalence of amantadine-resistant influenza A viruses. Phylogenies of the HA and NA genes were analyzed and mutations in M2 that confer resistance to amantadine were screened. Influenza in Myanmar exhibited seasonality, which coincided during the rainy season from June to August. Out of 2,618 samples, 76 influenza A and 132 influenza B viruses were isolated. Phylogenetic analysis showed that in 2005, 11 A/H1N1 isolates formed one cluster with A/Solomon Islands/3/2006 and were amantadine-sensitive strains. One A/H3N2 isolate was amantadine-resistant harboring S31N mutation in M2 and possessing S193F and D225N substitutions in HA (clade N), similar to A/Wisconsin/67/2005. No viruses were isolated in 2006 due to sample storage failure. In 2007, all 64 A/H3N2 isolates were amantadine-resistant and similar to A/Brisbane/10/2007. For influenza B, 3 Yamagata-lineage and 17 Victoria-lineage isolates were detected in 2005 and 112 Victoria-lineage viruses were isolated in 2007. All Victoria-lineage isolates were reassortants possessing NA derived from the Yamagata lineage. Continuous surveillance in tropical countries is important for elucidating the seasonality of influenza and determining the molecular characteristics of circulating strains.
    Intervirology 09/2009; 52(6):310-20. · 1.89 Impact Factor
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    ABSTRACT: Human respiratory syncytial virus (HRSV) is a common etiological agent of acute lower respiratory tract disease in infants. We report the molecular epidemiology of HRSV in Niigata, Japan, over six successive seasons (from 2001 to 2007) and the emerging genotypes of HRSV subgroup A (HRSV-A) strains. A total of 488 HRSV samples were obtained from 1,103 screened cases in a pediatric clinic in Niigata. According to the phylogenetic analysis, among the PCR-positive samples, 338 HRSV-A strains clustered into the previously reported genotypes GA5 and GA7 and two novel genotypes, NA1 and NA2, which were genetically close to GA2 strains. One hundred fifty HRSV-B strains clustered into three genotypes, namely, GB3, SAB3, and BA, which has a 60-nucleotide insertion in the second hypervariable region of the G protein. The NA1 strains emerged first, in the 2004-2005 season, and subsequently, the NA2 strain emerged in the 2005-2006 season. Both strains caused large epidemics in the 2005-2006 and 2006-2007 seasons. The average age of children who were infected with NA2 strains was significantly higher than that of those infected with GA5 and the frequency of reinfection by NA2 was the highest among all genotypes, suggesting that this genotype possessed new antigenicity for evading past host immunity. This is the first paper to show a possible correlation between an emerging genotype, NA2, and large outbreaks of HRSV in Japan. Continuing studies to follow up the genetic changes and to clarify the mechanism of reinfection in HRSV are important steps to understand HRSV infections.
    Journal of clinical microbiology 07/2009; 47(8):2475-82. · 4.16 Impact Factor
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    ABSTRACT: A total of 1,041 human influenza A virus isolates were collected at a clinic in Niigata, Japan, during eight influenza seasons from 2000 to 2007. The H3N2 subtype accounted for 75.4% of the isolates, and the rest were H1N1. Extremely high rates of amantadine-resistant strains of H3N2 subtype were observed in 2005/2006 (100%) and 2006/2007 (79.4%), while amantadine-resistant strains of H1N1 subtype were only detected in 2006/2007 (48.2%). Sequence and phylogenetic analysis of the HA1 subunit of the hemagglutinin (HA) gene revealed a characteristic linear trunk in the case of H3N2 viruses and a multi-furcated tree in the case of H1N1 and showed a higher sequence diversity among H3N2 strains than H1N1 strains. Mutations in the HA1 from both subtypes were mainly found in the globular region, and only one-third of these were retained for two or more successive years. Higher diversity of H3N2 viruses was mainly attributable to a higher fixation rate of non-synonymous mutations and to a lesser extent to a higher nucleotide substitution rate than for H1N1. Our analysis showed evidence of four positively selected sites in the HA1 of H1 and five sites in that of H3, four of which were novel. Finally, acquisition or loss of N-glycosylation sites was shown to contribute to the evolution of influenza A virus, especially in the case of H3N2, which had a higher tendency to acquire new glycosylation sites.
    Archives of Virology 02/2009; 154(2):285-95. · 2.28 Impact Factor

Publication Stats

403 Citations
92.26 Total Impact Points

Institutions

  • 2006–2014
    • Niigata University
      • • Division of Public Health
      • • Graduate School of Medical and Dental Sciences
      Niahi-niigata, Niigata, Japan
  • 2012
    • National Institute of Animal Health
      Tsukuba, Ibaraki, Japan
  • 2011
    • St. Jude Children's Research Hospital
      • Department of Infectious Diseases
      Memphis, TN, United States
  • 2010
    • University of Niigata Prefecture
      Niahi-niigata, Niigata, Japan
  • 2008
    • National Institute of Hygiene and Epidemiology
      Hà Nội, Ha Nội, Vietnam