Rapid emergence of oseltamivir resistance

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.

Persistence of pandemic influenza H1N1 virus in young patients after oseltamivir therapy in the 2009-2010 season: a comparison with seasonal H1N1 with or without H275Y mutation

Comparison of the viral persistence of pandemic H1N1 (H1N1pdm) and seasonal H1N1 with or without H275Y mutation after oseltamivir therapy has not been adequately done. Virus was isolated before and on days 4-6 from the start of oseltamivir treatment for 158 cases of seasonal (2007-2008 and 2008-2009 seasons) or pandemic (2009-2010 season) H1N1 influenza. Sequence analysis was done for each season and NA inhibition assay (IC(50)) was done in the 2009-2010 season. H275Y mutation before therapy was 0% in the 2007-2008 and 2009-2010 seasons, but 100% in the 2008-2009 season. Fever and other symptoms were noticeably prolonged after oseltamivir therapy for children with H275Y mutated seasonal H1N1 (2008-2009 season), but not in patients with seasonal H1N1 without mutation (2007-2008) or H1N1pdm (2009-2010). The viral persistence rate was significantly higher for patients 15 years or younger than for those 16 years and older with H275Y mutated seasonal H1N1 (46.2% and 10.5%, respectively) or with H1N1pdm (43.3% and 11.5%, respectively). The H275Y mutation emerged after oseltamivir treatment in 2.4% (2/82) of all patients with H1N1pdm. In two children, the H275Y mutation emerged after therapy and the IC(50) increased more than 200 fold; however, the prolongation of fever was not so prominent. In conclusion, oseltamivir was effective for fever and other clinical symptoms; however, the virus persisted longer than expected after treatment in H1N1pdm influenza-infected children in the 2009-2010 season, similar to seasonal H1N1 with H275Y mutation in the 2008-2009 season.

The seasonal influenza vaccine Agriflu(®)

Seasonal influenza continues to have a large impact annually. Combined with pneumonia, influenza is the sixth leading cause of death in the USA, and vaccination has been the most important tool to prevent it. Agriflu(®) is an egg-derived, subunit, nonadjuvanted trivalent inactivated vaccine indicated for immunization to prevent disease caused by influenza virus subtypes A and B contained in the vaccine. Agriflu was approved in the USA by the US FDA on 27 November 2009, for those aged 18 years and older, to prevent disease caused by influenza virus subtypes A and B. Based on clinical trial evidence, Agriflu has been shown to be safe, with <1% serious adverse event rates, and immunogenic. It has been proven to be highly effective to prevent culture-confirmed influenza and, thus, is an alternative to previously licensed seasonal influenza vaccines. Besides Fluvirin(®), Agriflu is the only subunit vaccine available in the USA. Owing to the economic burden, morbidity and mortality caused by seasonal influenza, addition of new, safe and effective vaccines to the available tools, to reduce the impact of influenza, is of importance and benefit, especially in the face of the recent shortages of influenza vaccines.

Environmental levels of the antiviral oseltamivir induce development of resistance mutation H274Y in influenza A/H1N1 virus in mallards

Oseltamivir (Tamiflu®) is the most widely used drug against influenza infections and is extensively stockpiled worldwide as part of pandemic preparedness plans. However, resistance is a growing problem and in 2008–2009, seasonal human influenza A/H1N1 virus strains in most parts of the world carried the mutation H274Y in the neuraminidase gene which causes resistance to the drug. The active metabolite of oseltamivir, oseltamivir carboxylate (OC), is poorly degraded in sewage treatment plants and surface water and has been detected in aquatic environments where the natural influenza reservoir, dabbling ducks, can be exposed to the substance. To assess if resistance can develop under these circumstances, we infected mallards with influenza A/H1N1 virus and exposed the birds to 80 ng/L, 1 µg/L and 80 µg/L of OC through their sole water source. By sequencing the neuraminidase gene from fecal samples, we found that H274Y occurred at 1 µg/L of OC and rapidly dominated the viral population at 80 µg/L. IC₅₀ for OC was increased from 2–4 nM in wild-type viruses to 400–700 nM in H274Y mutants as measured by a neuraminidase inhibition assay. This is consistent with the decrease in sensitivity to OC that has been noted among human clinical isolates carrying H274Y. Environmental OC levels have been measured to 58–293 ng/L during seasonal outbreaks and are expected to reach µg/L-levels during pandemics. Thus, resistance could be induced in influenza viruses circulating among wild ducks. As influenza viruses can cross species barriers, oseltamivir resistance could spread to human-adapted strains with pandemic potential disabling oseltamivir, a cornerstone in pandemic preparedness planning. We propose surveillance in wild birds as a measure to understand the resistance situation in nature and to monitor it over time. Strategies to lower environmental levels of OC include improved sewage treatment and, more importantly, a prudent use of antivirals.

Monitoring and characterization of oseltamivir-resistant pandemic (H1N1) 2009 virus, Japan, 2009-2010

No evidence of sustained spread was found, but 2 incidents of human-to-human transmission were suspected.

To monitor and characterize oseltamivir-resistant (OR) pandemic (H1N1) 2009 virus with the H275Y mutation, we analyzed 4,307 clinical specimens from Japan by neuraminidase (NA) sequencing or inhibition assay; 61 OR pandemic (H1N1) 2009 viruses were detected. NA inhibition assay and M2 sequencing indicated that OR pandemic (H1N1) 2009 virus was resistant to M2 inhibitors, but sensitive to zanamivir. Full-genome sequencing showed OR and oseltamivir-sensitive (OS) viruses had high sequence similarity, indicating that domestic OR virus was derived from OS pandemic (H1N1) 2009 virus. Hemagglutination inhibition test demonstrated that OR and OS pandemic (H1N1) 2009 viruses were antigenically similar to the A/California/7/2009 vaccine strain. Of 61 case-patients with OR viruses, 45 received oseltamivir as treatment, and 10 received it as prophylaxis, which suggests that most cases emerged sporadically from OS pandemic (H1N1) 2009, due to selective pressure. No evidence of sustained spread of OR pandemic (H1N1) 2009 was found in Japan; however, 2 suspected incidents of human-to-human transmission were reported.

Emergence of oseltamivir-resistant pandemic (H1N1) 2009 virus within 48 hours

An oseltamivir-resistant influenza A pandemic (H1N1) 2009 virus evolved and emerged from zero to 52% of detectable virus within 48 hours of a patient’s exposure to oseltamivir. Phylogenetic analysis and data gathered by pyrosequencing and cloning directly on clinical samples suggest that the mutant emerged de novo.

Treatment options for H5N1: lessons learned from the H1N1 pandemic

Human infections with avian influenza A (H5N1) are relatively rare but are associated with high mortality. As of July 5, 2010 there had been 500 cases and 296 fatalities. The influenza virus readily undergoes mutation and reassortment, and there are concerns that an H5N1 variant could be responsible for a future pandemic. The influenza neuraminidase inhibitors zanamivir and oseltamivir are approved for the treatment and prophylaxis of influenza. Oseltamivir is being used to treat H5N1 infections and the case has been made for a role for zanamivir; however, there are no case reports for the latter. Zanamivir is a potent inhibitor of H5N1, attains high lung concentrations immediately on administration, distributes into plasma at antiviral concentrations, has a low propensity for generating resistant virus, and retains activity against H275Y oseltamivir-resistant virus. There have been several reports of oseltamivir-resistant H5N1 arising during treatment with oseltamivir, and zanamivir retains effectiveness (in vitro or in vivo) against these isolates. Compassionate use of intravenous zanamivir for the treatment of seriously ill patients, including those with H275Y H1N1 infections, has also shown promising results. It is concluded that there is a role for zanamivir in treating H5N1 infections either as the approved, inhaled formulation in patients capable of using the Diskhaler, or as the intravenous formulation if compassionate use is warranted. The relatively small number of patients with these infections remains an obstacle to completion of clinical trials. Evidence is therefore likely to be based on carefully documented case reports, ideally in patients treated early in the course of the infection.

Viral membranes: an emerging antiviral target for enveloped viruses?

Evaluation of: Wolf MC, Freiberg AN, Zhang T et al. A broad-spectrum antiviral targeting entry of enveloped viruses. Proc. Natl Acad. Sci. USA 107, 3157-3162 (2010). The emergence and re-emergence of viruses and the widespread antiviral resistance calls for the development of a broad-spectrum strategy for viral infection. The article under review describes an approach to achieve this goal by developing an antiviral rhodanine derivative effective against enveloped viruses targeting the viral lipid membrane. By intercalating into the viral membrane, the compound irreversibly inactivates the virions with virucidal effects. Potential toxic effects on hosts could be minimized by continuous regeneration of cellular membranes. The present strategy exploits the therapeutic window that exists between static viral membranes and biogenic cellular membranes and provides a useful guideline for future research endeavors towards broad-spectrum antiviral approaches for enveloped viruses. Developing a formulation that ensures efficient delivery and pharmacokinetic properties while minimizing systemic toxicity on cell membranes remains a challenge. The advantages and disadvantages of a viral membrane-targeting approach for the control of emerging and re-emerging viruses will be discussed.

Historical review of pandemic influenza A in Taiwan, 2009

Influenza is an important disease in children. In April 2009, human infections caused by a novel swine H1N1 virus were reported in Mexico, followed by a pandemic. As of 14 March 2010, more than 213 countries and overseas territories or communities have reported laboratory-confirmed cases of pandemic influenza H1N1 2009, including at least 16,813 deaths. This influenza pandemic is unique in many respects. Large outbreaks occurred outside the usual season for influenza infection. The virus also caused severe illnesses and deaths in younger people, with many deaths caused by severe pneumonia. A comprehensive approach to pandemic control has been launched, including infection control interventions, antiviral drugs and vaccines. Vaccination is the most efficient way to control morbidity and mortality resulting from influenza infections in humans. For the first time, an influenza vaccine against a pandemic strain became available before the winter. However, the initially smooth influenza vaccination program was disturbed by the fear of possible adverse events following immunization. In Taiwan, mistrust of the influenza vaccination has also caused significant social impacts towards the end of 2009. Lessons learned from this pandemic influenza H1N1 2009 might help health authorities and physicians shape their preparedness for the next pandemic.