Neuraminidase Inhibitor Susceptibility Research Articles

The I427T neuraminidase (NA) substitution, located outside the NA active site of an influenza A(H1N1)pdm09 variant with reduced susceptibility to NA inhibitors, alters NA properties and impairs viral fitness

Emergence of pan neuraminidase inhibitor (NAI)-resistant variants constitutes a serious clinical concern. An influenza A(H1N1)pdm09 variant containing the I427T/Q313R neuraminidase (NA) substitutions was previously identified in a surveillance study. Although these changes are not part of the NA active site, the variant showed reduced susceptibility to many NAIs. In this study, we investigated the mechanism of resistance for the I427T/Q313R substitution and its impact on the NA enzyme and viral fitness. Recombinant wild-type (WT), I427T/Q313R and I427T A(H1N1)pdm09 viruses were generated by reverse genetics and tested for their drug susceptibilities, enzymatic properties and replication kinetics in vitro as well as their virulence in mice. Molecular dynamics (MD) simulations were performed for NA structural analysis. The I427T substitution, which was responsible for the resistance phenotype observed in the double (I427T/Q313R) mutant, induced 17-, 56-, 7-, and 14-fold increases in IC50 values against oseltamivir, zanamivir, peramivir and laninamivir, respectively. The I427T substitution alone or combined to Q313R significantly reduced NA affinity. The I427T/Q313R and to a lesser extent I427T recombinant viruses displayed reduced viral titers vs WT in vitro. In experimentally-infected mice, the mortality rates were 62.5%, 0% and 14.3% for the WT, I417T/Q313R and I427T viruses, respectively. There were about 2.5- and 2-Log reductions in mean lung viral titers on day 5 post-infection for the I427T/Q313R and I427T mutants, respectively, compared to WT. Results from simulations revealed that the I427T change indirectly altered the stability of the catalytic R368 residue of the NA enzyme causing its reduced binding to the substrate/inhibitor. This study demonstrates that the I427T/Q313R mutant, not only alters NAI susceptibility but also compromises NA properties and viral fitness, which could explain its infrequent detection in clinic.

Peramivir susceptibilities of recombinant influenza A and B variants selected with various neuraminidase inhibitors.

Peramivir is a parenteral neuraminidase inhibitor (NAI) approved for treating influenza infections in a few countries. We determined peramivir susceptibilities of several uncharacterized influenza A and B neuraminidase (NA) and haemagglutinin (HA) mutants selected with different NAIs. Recombinant wild-type (WT) and mutant NA proteins were expressed in 293T cells and susceptibility to peramivir, oseltamivir and zanamivir was determined by NA inhibition assay using the MUNANA substrate. Recombinant/reassortant influenza A(H1N1), A(H3N2) and B HA mutants were rescued by reverse genetics and assessed by plaque size or viral yield assays for drug susceptibility. Recombinant R152K, I222K/T, G248R+I266V, Q312R+I427T and R371K (A[H1N1]pdm09); E41G, 1222L/V, Q226H and S247P (A[H3N2]) and D198Y, A246D/S/T and G402S (B) mutant NA proteins (N2 numbering) were analysed. Peramivir exhibited the lowest IC50 values against both influenza A and B WT NAs. Peramivir and oseltamivir generally shared similar phenotypes. Of note, peramivir retained activity against I222K/T (A[H1N1]pdm09), I222L/V (A[H3N2]) and A246T (B) mutants, which had reduced inhibition (RI) or highly RI (HRI) against oseltamivir. Cross-RI/HRI against the three NAIs was observed for R152K, R371K and Q312R+I427T (A[H1N1]pdm09); S247P (A[H3N2]) and D198Y (B) mutants. All tested recombinant/reassortant R208K (A/Puerto Rico/8/34 [H1N1]); A28T, R124M and K189E (A/Victoria/3/75 [H3N2]) and T139N (B/Phuket/3073/13) HA mutants were susceptible to peramivir in cell culture experiments. Peramivir is highly active against seasonal influenza subtypes. Although peramivir and oseltamivir generally share similar phenotypes, peramivir still possesses activity against some variants with RI/HRI against oseltamivir. Finally, NAI-induced HA substitutions alone did not significantly impact NAI susceptibility.

Epidemiological, Clinical and Virological Characteristics of Influenza B Virus from Patients at the Hospital Tertiary Care Units in Bangkok during 2011-2014.

Influenza B virus, which causes acute respiratory infections, has increased in prevalence in recent years. Based on the nucleotide sequence of the hemagglutinin (HA) gene, influenza B virus can be divided into two lineages, Victoria and Yamagata, that co-circulate during the influenza season. However, analysis of the potential association between the clinical and virological characteristic and the lineage of influenza B viruses isolated in Thailand was lacking. To investigate influenza B virus genetically and determine its neuraminidase (NA) inhibitor susceptibility phenotype, a total of 6920 nasopharyngeal-wash samples were collected from patients with influenza-like illness between the years 2011 and 2014 and were screened for influenza B virus by real-time PCR. Of these samples, 3.1% (216/6920) were confirmed to contain influenza B viruses, and 110 of these influenza viruses were randomly selected for nucleotide sequence analysis of the HA and NA genes. Phylogenetic analysis of the HA sequences showed clustering into various clades: Yamagata clade 3 (11/110, 10%), Yamagata clade 2 (71/110, 64.5%), and Victoria clade 1 (28/110, 25.5%). The analysis of clinical characteristic demonstrated that the Victoria lineage was significantly associated with the duration of hospitalization, number of deceased cases, pneumonia, secondary bacterial infection and underlying disease. When combined with phylogenetic analysis of the NA sequences, four samples showed viruses with reassortant sequences between the Victoria and Yamagata lineages. Statistical analysis of the clinical outcomes and demographic data for the reassortant strains did not differ from those of the other strains in circulation. Oseltamivir-resistant influenza B viruses were not detected. Our findings indicated the co-circulation of the Victoria and Yamagata lineages over the past four cold seasons in Bangkok. We also demonstrated differences in the clinical symptoms between these lineages.

Detection of influenza B viruses with reduced sensitivity to neuraminidase inhibitor in Morocco during 2014/15 season

We monitored phenotypic and genotypic susceptibility of influenza viruses circulating in Morocco during 2014-2015 to oseltamivir and zanamivir. Throat and nasal swab specimens were collected from outpatients (with influenza-like illness) and inpatients (with severe acute respiratory illness) and tested for influenza viruses using real-time reverse transcription polymerase chain reaction. Positive samples were inoculated in MDCK cells and virus phenotypic susceptibility to neuraminidase inhibitors (NAIs) was assessed using fluorescent NA inhibition. Of 440 specimens, 135 were positive for influenza B Yamagata-like virus, 38 were A(H1N1)pdm09 and 25 were A(H3N2). Sixty influenza B viruses isolated from MDCK cells showed no significant resistance to NAIs. However, two of these strains, B/Morocco/176H/2015 and B/Morocco/CP10/2015, showed reduced susceptibility to oseltamivir. The two influenza B viruses with reduced susceptibility to oseltamivir show that ongoing NAI susceptibility surveillance is essential.

Sequence diversity of NanA manifests in distinct enzyme kinetics and inhibitor susceptibility.

Streptococcus pneumoniae is the leading pathogen causing bacterial pneumonia and meningitis. Its surface-associated virulence factor neuraminidase A (NanA) promotes the bacterial colonization by removing the terminal sialyl residues from glycoconjugates on eukaryotic cell surface. The predominant role of NanA in the pathogenesis of pneumococci renders it an attractive target for therapeutic intervention. Despite the highly conserved activity of NanA, our alignment of the 11 NanAs revealed the evolutionary diversity of this enzyme. The amino acid substitutions we identified, particularly those in the lectin domain and in the insertion domain next to the catalytic centre triggered our special interest. We synthesised the representative NanAs and the mutagenized derivatives from E. coli for enzyme kinetics study and neuraminidase inhibitor susceptibility test. Via molecular docking we got a deeper insight into the differences between the two major variants of NanA and their influence on the ligand-target interactions. In addition, our molecular dynamics simulations revealed a prominent intrinsic flexibility of the linker between the active site and the insertion domain, which influences the inhibitor binding. Our findings for the first time associated the primary sequence diversity of NanA with the biochemical properties of the enzyme and with the inhibitory efficiency of neuraminidase inhibitors.

Standardizing the influenza neuraminidase inhibition assay among United States public health laboratories conducting virological surveillance

BackgroundMonitoring influenza virus susceptibility to neuraminidase (NA) inhibitors (NAIs) is vital for detecting drug-resistant variants, and is primarily assessed using NA inhibition (NI) assays, supplemented by NA sequence analysis. However, differences in NI testing methodologies between surveillance laboratories results in variability of 50% inhibitory concentration (IC50) values, which impacts data sharing, reporting and interpretation. In 2011, the Centers for Disease Control and Prevention (CDC), in collaboration with the Association for Public Health Laboratories (APHL) spearheaded efforts to standardize fluorescence-based NI assay testing in the United States (U.S.), with the goal of achieving consistency of IC50 data. MethodsFor the standardization process, three participating state public health laboratories (PHLs), designated as National Surveillance Reference Centers for Influenza (NSRC-Is), assessed the NAI susceptibility of the 2011–12 CDC reference virus panel using stepwise procedures, with support from the CDC reference laboratory. Next, the NSRC-Is assessed the NAI susceptibility of season 2011–12 U.S. influenza surveillance isolates (n = 940), with a large subset (n = 742) tested in parallel by CDC. Subsequently, U.S. influenza surveillance isolates (n = 9629) circulating during the next three influenza seasons (2012–15), were independently tested by the three NSRC-Is (n = 7331) and CDC (n = 2298). ResultsThe NI assay IC50s generated by respective NSRC-Is using viruses and drugs prepared by CDC were similar to those obtained with viruses and drugs prepared in-house, and were uniform between laboratories. IC50s for U.S. surveillance isolates tested during four consecutive influenza seasons (2011–15) were consistent from season to season, within and between laboratories. ConclusionThese results show that the NI assay is robust enough to be standardized, marking the first time IC50 data have been normalized across multiple laboratories, and used for U.S. national NAI susceptibility surveillance.

Zanamivir-resistant influenza viruses with Q136K or Q136R neuraminidase residue mutations can arise during MDCK cell culture creating challenges for antiviral susceptibility monitoring

Surveillance of circulating influenza strains for antiviral susceptibility is important to ensure patient treatment guidelines remain appropriate. Influenza A(H3N2) and A(H1N1)pdm09 virus isolates containing mutations at the Q136 residue of the neuraminidase (NA) that conferred reduced susceptibility to the NA inhibitor (NAI) zanamivir were detected during antiviral susceptibility monitoring. Interestingly, the mutations were not detectable in the viruses from respective clinical specimens, only in the cultured isolates. We showed that variant viruses containing the Q136K and Q136R NA mutations were preferentially selected in Madin-Darby canine kidney epithelial (MDCK) cells, but were less well supported in MDCK-SIAT1 cells and embryonated eggs. The effect of Q136K, Q136R, Q136H and Q136L substitutions in NA subtypes N1 and N2 on NAI susceptibility and in vitro viral fitness was assessed. This study highlights the challenges that cell culture derived mutations can pose to the NAI susceptibility analysis and interpretation and reaffirms the need to sequence viruses from respective clinical specimens to avoid misdiagnosis. However, we also demonstrate that NA mutations at residue Q136 can confer reduced zanamivir, peramivir or laninamivir susceptibility, and therefore close monitoring of viruses for mutations at this site from patients being treated with these antivirals is important.

Investigational rapid multiplex assay for the detection of influenza and respiratory syncytial viruses using the Iidylla™ system demonstrates exceptional performance & flexibility with minimal hands-on time

Four World Health Organization (WHO) Collaborating Centres for Reference and Research on Influenza and one WHO Collaborating Centre for the Surveillance, Epidemiology and Control of Influenza (WHO CCs) tested 10,641 viruses collected by WHO-recognized National Influenza Centres between May 2013 and May 2014 to determine 50% inhibitory concentration (IC50) data for neuraminidase inhibitors (NAIs) oseltamivir, zanamivir, peramivir and laninamivir. In addition, neuraminidase (NA) sequence data, available from the WHO CCs and from sequence databases (n = 3206), were screened for amino acid substitutions associated with reduced NAI susceptibility. Ninety-five per cent of the viruses tested by the WHO CCs were from three WHO regions: Western Pacific, the Americas and Europe. Approximately 2% (n = 172) showed highly reduced inhibition (HRI) against at least one of the four NAIs, commonly oseltamivir, while 0.3% (n = 32) showed reduced inhibition (RI). Those showing HRI were A(H1N1)pdm09 with NA H275Y (n = 169), A(H3N2) with NA E119V (n = 1), B/Victoria-lineage with NA E117G (n = 1) and B/Yamagata-lineage with NA H273Y (n = 1); amino acid position numbering is A subtype and B type specific. Although approximately 98% of circulating viruses tested during the 2013–2014 period were sensitive to all four NAIs, a large community cluster of A(H1N1)pdm09 viruses with the NA H275Y substitution from patients with no previous exposure to antivirals was detected in Hokkaido, Japan. Significant numbers of A(H1N1)pdm09 NA H275Y viruses were also detected in China and the United States: phylogenetic analyses showed that the Chinese viruses were similar to those from Japan, while the United States viruses clustered separately from those of the Hokkaido outbreak, indicative of multiple resistance-emergence events. Consequently, global surveillance of influenza antiviral susceptibility should be continued from a public health perspective.

Influenza viruses with B/Yamagata- and B/Victoria-like neuraminidases are differentially affected by mutations that alter antiviral susceptibility.

The burden of disease due to influenza B is often underestimated. Clinical studies have shown that oseltamivir, a widely used neuraminidase inhibitor (NAI) antiviral drug, may have reduced effectiveness against influenza B viruses. Therefore, it is important to study the effect of neuraminidase mutations in influenza B viruses that may further reduce NAI susceptibility, and to determine whether these mutations have the same effect in the two lineages of influenza B viruses that are currently circulating (B/Yamagata-like and B/Victoria-like). We characterized the effect of 16 amino acid substitutions across five framework residues and four monomeric interface residues on the susceptibility to four different NAIs (oseltamivir, zanamivir, peramivir and laninamivir). Framework residue mutations E117A and E117G conferred highly reduced inhibition to three of the four NAIs, but substantially reduced neuraminidase activity, whereas other framework mutations retained a greater level of NA activity. Mutations E105K, P139S and G140R of the monomeric interface were also found to cause highly reduced inhibition, but, interestingly, their effect was substantially greater in a B/Victoria-like neuraminidase than in a B/Yamagata-like neuraminidase, with some susceptibility values being up to 1000-fold different between lineages. The frequency and the effect of key neuraminidase mutations on neuraminidase activity and NAI susceptibility can differ substantially between the two influenza B lineages. Therefore, future surveillance, analysis and interpretation of influenza B virus NAI susceptibility should consider the B lineage of the neuraminidase in the same manner as already occurs for different influenza A neuraminidase subtypes.

Global update on the susceptibility of human influenza viruses to neuraminidase inhibitors, 2013–2014

Four World Health Organization (WHO) Collaborating Centres for Reference and Research on Influenza and one WHO Collaborating Centre for the Surveillance, Epidemiology and Control of Influenza (WHO CCs) tested 10,641 viruses collected by WHO-recognized National Influenza Centres between May 2013 and May 2014 to determine 50% inhibitory concentration (IC50) data for neuraminidase inhibitors (NAIs) oseltamivir, zanamivir, peramivir and laninamivir. In addition, neuraminidase (NA) sequence data, available from the WHO CCs and from sequence databases (n=3206), were screened for amino acid substitutions associated with reduced NAI susceptibility. Ninety-five per cent of the viruses tested by the WHO CCs were from three WHO regions: Western Pacific, the Americas and Europe. Approximately 2% (n=172) showed highly reduced inhibition (HRI) against at least one of the four NAIs, commonly oseltamivir, while 0.3% (n=32) showed reduced inhibition (RI). Those showing HRI were A(H1N1)pdm09 with NA H275Y (n=169), A(H3N2) with NA E119V (n=1), B/Victoria-lineage with NA E117G (n=1) and B/Yamagata-lineage with NA H273Y (n=1); amino acid position numbering is A subtype and B type specific. Although approximately 98% of circulating viruses tested during the 2013–2014 period were sensitive to all four NAIs, a large community cluster of A(H1N1)pdm09 viruses with the NA H275Y substitution from patients with no previous exposure to antivirals was detected in Hokkaido, Japan. Significant numbers of A(H1N1)pdm09 NA H275Y viruses were also detected in China and the United States: phylogenetic analyses showed that the Chinese viruses were similar to those from Japan, while the United States viruses clustered separately from those of the Hokkaido outbreak, indicative of multiple resistance-emergence events. Consequently, global surveillance of influenza antiviral susceptibility should be continued from a public health perspective.

Molecular epidemiology of influenza A virus infection among hospitalized children in Vietnam during post-pandemic period.

Genetic variability makes influenza virus to escape the immunity and causes yearly epidemics. Monitoring those changes is necessary for vaccine selection. In addition, H3N2 viruses were considered to be seeded from Southeast Asia before spreading globally. This study described the molecular epidemiology of influenza A during the post‐pandemic season 2010–2011 in Vietnam. Nasopharyngeal samples were collected from children with respiratory infections at Children's Hospital 2, Ho Chi Minh City. The HA, NA, M genes were amplified, sequenced and analyzed. Thirty‐five of 1,082 (3.2%) patients were positive for influenza A, including 14 pandemic H1N1 2009 (H1N1pdm09) and 21 H3N2 infections. H3N2 was dominant in the rainy season (May–October 2010) while H1N1pdm09 was dominant in the dry season (November 2010–April 2011). Phylogenetic analysis showed that Vietnamese H1N1pdm09 sequences in 2010–2011 formed the distinct cluster, with other contemporary Asian and 2012‐American sequences, suggesting a possible common ancestor. All were oseltamivir‐sensitive except two strains carrying S247N and D199N in NA which reduced the neuraminidase inhibitor susceptibility. The Vietnamese H3N2 viruses in mid‐2010 belonged to the emerging subclade Perth10/2010, which then spread worldwide in 2011. The Vietnamese influenza viruses were well matched with the Southern Hemisphere vaccine formulation. Mutations at antigenic sites were also identified in these viruses. Surveillance of influenza viruses in tropical countries is important not only for development of their prevention and control strategies but also for earlier identification of the newly emerged strains that may be selected for future vaccine. J. Med. Virol. 87:904–912, 2015. © 2015 Wiley Periodicals, Inc.

Molecular surveillance of antiviral drug resistance of influenza A/H3N2 virus in Singapore, 2009-2013.

Adamantanes and neuraminidase inhibitors (NAIs) are two classes of antiviral drugs available for the chemoprophylaxis and treatment of influenza infections. To determine the frequency of drug resistance in influenza A/H3N2 viruses in Singapore, large-scale sequencing of neuraminidase (NA) and matrix protein (MP) genes was performed directly without initial culture amplification. 241 laboratory-confirmed influenza A/H3N2 clinical samples, collected between May 2009 and November 2013 were included. In total, 229 NA (95%) and 241 MP (100%) complete sequences were obtained. Drug resistance mutations in the NA and MP genes were interpreted according to published studies. For the NAIs, a visual inspection of the aligned NA sequences revealed no known drug resistant genotypes (DRGs). For the adamantanes, the well-recognised S31N DRG was identified in all 241 MP genes. In addition, there was an increasing number of viruses carrying the combination of D93G+Y155F+D251V (since May 2013) or D93G (since March 2011) mutations in the NA gene. However, in-vitro NAI testing indicated that neither D93G+Y155F+D251V nor D93G alone conferred any changes in NAI susceptibility. Lastly, an I222T mutation in the NA gene that has previously been reported to cause oseltamivir-resistance in influenza A/H1N1/2009, B, and A/H5N1, was detected from a treatment-naïve patient. Further in-vitro NAI testing is required to confirm the effect of this mutation in A/H3N2 virus.

Oseltamivir-resistant influenza A(H1N1)pdm09 viruses, United States, 2013-14.

We report characteristics of oseltamivir-resistant influenza A(H1N1)pdm09 viruses and patients infected with these viruses in the United States. During 2013–14, fifty-nine (1.2%) of 4,968 analyzed US influenza A(H1N1)pdm09 viruses had the H275Y oseltamivir resistance–conferring neuraminidase substitution. Our results emphasize the need for local surveillance for neuraminidase inhibitor susceptibility among circulating influenza viruses.

Viral genome and antiviral drug sensitivity analysis of two patients from a family cluster caused by the influenza A(H7N9) virus in Zhejiang, China, 2013

In the winter of 2013, people were facing the risk of human-to-human transmission of the re-emerging influenza A(H7N9) virus. We report herein information on the clinical features of two patients from the same family infected with this virus, the genomic sequences of the viruses harbored, and antiviral drug sensitivity. Clinical and epidemiological data of two patients from the same family were collected and analyzed. Sequencing was done for the viruses isolated from these two patients and one epidemiologically related chicken, and the sequences of the eight gene segments of the viruses were analyzed phylogenetically. The sensitivity of the viruses to antiviral drug treatment was determined by neuraminidase inhibitor susceptibility test. The two patients from one family cluster shared the same symptoms but had different outcomes, and had a strong epidemiological link. Three strains, two from these two patients and one from the chicken, were isolated. Genome sequencing and analyses of phylogenetic trees demonstrated that the two viruses were almost identical. We noted the presence of the PB2 E627K amino acid substitution that was not present in isolates from the first wave, as well as two new mutations in the NA gene and six in the PB2 gene. Drug sensitivity testing showed that the new isolates were resistant to oseltamivir but sensitive to peramivir. The two patients from one family cluster were probable human-to-human transmission cases. The new isolates were sensitive to peramivir but showed reduced sensitivity to oseltamivir.

Characterization of drug-resistant influenza A(H7N9) variants isolated from an oseltamivir-treated patient in Taiwan.

Patients contracting influenza A(H7N9) infection often developed severe disease causing respiratory failure. Neuraminidase (NA) inhibitors (NAIs) are the primary option for treatment, but information on drug-resistance markers for influenza A(H7N9) is limited. Four NA variants of A/Taiwan/1/2013(H7N9) virus containing a single substitution (NA-E119V, NA-I222K, NA-I222R, or NA-R292K) recovered from an oseltamivir-treated patient were tested for NAI susceptibility in vitro; their replicative fitness was evaluated in cell culture, mice, and ferrets. NA-R292K led to highly reduced inhibition by oseltamivir and peramivir, while NA-E119V, NA-I222K, and NA-I222R caused reduced inhibition by oseltamivir. Mice infected with any virus showed severe clinical signs with high mortality rates. NA-I222K virus was the most virulent in mice, whereas virus lacking NA change (NA-WT) and NA-R292K virus seemed the least virulent. Sequence analysis suggests that PB2-S714N increased virulence of NA-I222K virus in mice; NS1-K126R, alone or in combination with PB2-V227M, produced contrasting effects in NA-WT and NA-R292K viruses. In ferrets, all viruses replicated to high titers in the upper respiratory tract but produced only mild illness. NA-R292K virus, showed reduced replicative fitness in this animal model. Our data highlight challenges in assessment of the replicative fitness of H7N9 NA variants that emerged in NAI-treated patients.

Influenza A(H1N1)pdm09 resistance and cross-decreased susceptibility to oseltamivir and zanamivir antiviral drugs.

Neuraminidase inhibitors (NAIs) oseltamivir and zanamivir are currently the only effective antiviral drugs available worldwide for the management of influenza. The potential development of resistance is continually threatening their use, rationalizing and highlighting the need for a close and sustained evaluation of virus susceptibility. This study aimed to analyze and characterize the phenotypic and genotypic NAIs susceptibility profiles of A(H1N1)pdm09 viruses circulating in Portugal from 2009 to 2010/2011. A total of 144 cases of A(H1N1)pdm09 virus infection from community and hospitalized patients were studied, including three suspected cases of clinical resistance to oseltamivir. Oseltamivir resistance was confirmed for two of the suspected cases. Neuraminidase (NA) H275Y resistant marker was found in viruses from both cases but for one it was only present in 26.2% of virus population, raising questions about the minimal percentage of resistant virus that should be considered relevant. Cross-decreased susceptibility to oseltamivir and zanamivir (2-4 IC50 fold-change) was detected on viruses from two potentially linked community patients from 2009. Both viruses harbored the NA I223V mutation. NA Y155H mutation was found in 18 statistical non-outlier viruses from 2009, having no impact on virus susceptibility. The mutations at NA N369K and V241I may have contributed to the significantly higher baseline IC50 value obtained to oseltamivir for 2010/2011 viruses, compared to viruses from the pandemic period. These results may contribute to a better understanding of the relationship between phenotype and genotype, which is currently challenging, and to the global assessment of A(H1N1)pdm09 virus susceptibility profile and baseline level to NAIs.

Global update on the susceptibility of human influenza viruses to neuraminidase inhibitors, 2012–2013

Emergence of influenza viruses with reduced susceptibility to neuraminidase inhibitors (NAIs) is sporadic, often follows exposure to NAIs, but occasionally occurs in the absence of NAI pressure. The emergence and global spread in 2007/2008 of A(H1N1) influenza viruses showing clinical resistance to oseltamivir due to neuraminidase (NA) H275Y substitution, in the absence of drug pressure, warrants continued vigilance and monitoring for similar viruses. Four World Health Organization (WHO) Collaborating Centres for Reference and Research on Influenza and one WHO Collaborating Centre for the Surveillance, Epidemiology and Control of Influenza (WHO CCs) tested 11,387 viruses collected by WHO-recognized National Influenza Centres (NIC) between May 2012 and May 2013 to determine 50% inhibitory concentration (IC50) data for oseltamivir, zanamivir, peramivir and laninamivir. The data were evaluated using normalized IC50 fold-changes rather than raw IC50 data. Nearly 90% of the 11,387 viruses were from three WHO regions: Western Pacific, the Americas and Europe. Only 0.2% (n=27) showed highly reduced inhibition (HRI) against at least one of the four NAIs, usually oseltamivir, while 0.3% (n=39) showed reduced inhibition (RI). NA sequence data, available from the WHO CCs and from sequence databases (n=3661), were screened for amino acid substitutions associated with reduced NAI susceptibility. Those showing HRI were A(H1N1)pdm09 with NA H275Y (n=18), A(H3N2) with NA E119V (n=3) or NA R292K (n=1) and B/Victoria-lineage with NA H273Y (n=2); amino acid position numbering is A subtype and B type specific. Overall, approximately 99% of circulating viruses tested during the 2012–2013 period were sensitive to all four NAIs. Consequently, these drugs remain an appropriate choice for the treatment and prophylaxis of influenza virus infections.

Fitness Costs for Influenza B Viruses Carrying Neuraminidase Inhibitor-Resistant Substitutions: Underscoring the Importance of E119A and H274Y

Influenza B viruses cause annual outbreaks of respiratory illness in humans and are increasingly recognized as a major cause of influenza-associated pediatric mortality. Neuraminidase (NA) inhibitors (NAIs) are the only available therapy for patients infected with influenza B viruses, and the potential emergence of NAI-resistant viruses is a public health concern. The NA substitutions located within the enzyme active site could not only reduce NAI susceptibility of influenza B virus but also affect virus fitness. In this study, we investigated the effect of single NA substitutions on the fitness of influenza B/Yamanashi/166/1998 viruses (Yamagata lineage). We generated recombinant viruses containing either wild-type (WT) NA or NA with a substitution in the catalytic (R371K) or framework (E119A, D198E, D198Y, I222T, H274Y, and N294S) residues. We assessed NAI susceptibility, NA biochemical properties, NA protein expression, and virus replication in vitro and in differentiated normal human bronchial epithelial (NHBE) cells. Our results showed that four NA substitutions (D198E, I222T, H274Y, and N294S) conferred reduced inhibition by oseltamivir and three (E119A, D198Y, and R371K) conferred highly reduced inhibition by oseltamivir, zanamivir, and peramivir. All NA substitutions, except for D198Y and R371K, were genetically stable after seven passages in MDCK cells. Cell surface NA protein expression was significantly increased by H274Y and N294S substitutions. Viruses with the E119A, I222T, H274Y, or N294S substitution were not attenuated in replication efficiency in vitro or in NHBE cells. Overall, viruses with the E119A or H274Y NA substitution possess fitness comparable to NAI-susceptible virus, and the acquisition of these substitutions by influenza B viruses should be closely monitored.

Antiviral Susceptibility of Variant Influenza A(H3N2)v Viruses Isolated in the United States from 2011 to 2013

Since 2011, outbreaks caused by influenza A(H3N2) variant [A(H3N2)v] viruses have become a public health concern in the United States. The A(H3N2)v viruses share the A(H1N1)pdm09 M gene containing the marker of M2 blocker resistance, S31N, but do not contain any known molecular markers associated with resistance to neuraminidase (NA) inhibitors (NAIs). Using a fluorescent NA inhibition (NI) assay, the susceptibilities of recovered A(H3N2)v viruses (n=168) to FDA-approved (oseltamivir and zanamivir) and other (peramivir, laninamivir, and A-315675) NAIs were assessed. All A(H3N2)v viruses tested, with the exception of a single virus strain, A/Ohio/88/2012, isolated from an untreated patient, were susceptible to the NAIs tested. The A/Ohio/88/2012 virus contained two rare substitutions, S245N and S247P, in the NA and demonstrated reduced inhibition by oseltamivir (31-fold) and zanamivir (66-fold) in the NI assay. Using recombinant NA (recNA) proteins, S247P was shown to be responsible for the observed altered NAI susceptibility, in addition to an approximately 60% reduction in NA enzymatic activity. The S247P substitution has not been previously reported as a molecular marker of reduced susceptibility to the NAIs. Using cell culture assays, the investigational antiviral drugs nitazoxanide, favipiravir, and fludase were shown to inhibit the replication of A(H3N2)v viruses, including the virus with the S247P substitution in the NA. This report demonstrates the importance of continuous monitoring of susceptibility of zoonotic influenza viruses to available and investigational antiviral drugs.

Neuraminidase inhibitor susceptibility profile of pandemic and seasonal influenza viruses during the 2009–2010 and 2010–2011 influenza seasons in Japan

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.