Genomic diversity of oseltamivir-resistant influenza virus A (H1N1), Luxembourg, 2007-08

Recombinant A(H6N1)-H274Y avian influenza virus with dual drug resistance does not require permissive mutations to retain the replicative fitness in vitro and in ovo

The possible emergence of drug-resistant avian flu raises concerns over the limited effectiveness of currently approved antivirals (neuraminidase inhibitors - NAIs) in the hypothetical event of a zoonotic spillover. Our study demonstrated that the recombinant avian A(H6N1) viruses showed reduced inhibition (RI) by multiple NAI drugs following the introduction of point mutations found predominantly in the neuraminidase gene (NA) of NAI-resistant human influenza strains (E119V, R292K and H274Y; N2 numbering). Moreover, A(H6N1)-H274Y showed increased replication efficiency in vitro, and a fitness advantage over wild-type (WT) when co-inoculated into embryonated hen's eggs. The results presented in our study together with the zoonotic potential of the A(H6N1) virus as evidenced by the human infection from 2013, highlight the need for enhanced monitoring of NAI resistance-associated signatures in circulating LPAI (low pathogenic avian influenza) globally.

[Factors related to death by the Pandemic Influenza A (H1N1) 2009 in patients treated with oseltamivir]

This study aimed to identify factors related to death in Pandemic Influenza A(H1N1)2009 in patients treated with Oseltamivir. It is an observational and retrospective study, carried out with data of patients who had presented laboratorial diagnosis of the illness. Data were collected from the notification forms of the disease, belonging to a database of the Ministry of Health. Statistical analysis was performed by chi-square, Student t test and logistic regression, considering significant p values <0,05. The highest mortality was observed in patients aged between 20 and 59 years, low schooling, with the presence of comorbidities, not vaccinated, treated late and had more severe symptoms of infection. The identification of risk factors for death reinforces the need for prevention and early care, especially in the presence of factors that increase the clinical severity of disease.

Effect of oseltamivir carboxylate consumption on emergence of drug-resistant H5N2 avian influenza virus in Mallard ducks

Oseltamivir carboxylate (OC) has been detected in environmental waters at various levels during recent influenza seasons in humans, reflecting levels of usage and stability of this drug. In consideration of the role of waterfowl as hosts for influenza viruses that may contribute to human infections, we evaluated the effect of consumption of low doses of OC on development of oseltamivir-resistant influenza virus mutants in mallard ducks (Anas platyrhynchos) infected with two different low-pathogenic (LP) H5N2 avian influenza viruses (AIV). We detected development of virus variants carrying a known molecular marker of oseltamivir resistance (neuraminidase E119V) in 4 out of 6 mallards infected with A/Mallard/Minnesota/182742/1998 (H5N2) and exposed to 1,000 ng/liter OC. The mutation first appeared as a minor population on days 5 to 6 and was the dominant genotype on days 6 to 8. Oseltamivir-resistant mutations were not detected in virus from ducks not exposed to the drug or in ducks infected with a second strain of virus and similarly exposed to OC. Virus isolates carrying the E119V mutation displayed in vitro replication kinetics similar to those of the wild-type virus, but in vivo, the E119V virus rapidly reverted back to wild type in the absence of OC, and only the wild-type parental strain was transmitted to contact ducks. These results indicate that consumption by wild waterfowl of OC in drinking water may promote selection of the E119V resistance mutation in some strains of H5N2 AIV that could contribute to viruses infecting human populations.

The proton translocation domain of cellular vacuolar ATPase provides a target for the treatment of influenza A virus infections

BACKGROUND AND PURPOSE

Cellular vacuolar ATPases (v-ATPase) play an important role in endosomal acidification, a critical step in influenza A virus (IAV) host cell infection. We investigated the antiviral activity of the v-ATPase inhibitor saliphenylhalamide (SaliPhe) and compared it with several older v-ATPase inhibitors concanamycin A, bafilomycin A1, (BafA) and archazolid B targeting the subunit c of the V(0) sector.

EXPERIMENTAL APPROACH

An in vitro assay was devised to quantify the anti-influenza effect of v-ATPase inhibitors by measuring green fluorescent protein fluorescence of a reporter IAV. These data were combined with cytotoxicity testing to calculate selectivity indices. Data were validated by testing v-ATPase inhibitors against wild-type IAV in vitro and in vivo in mice.

KEY RESULTS

In vitro SaliPhe blocked the proliferation of pandemic and multidrug resistant viruses at concentrations up to 51-fold below its cytotoxic concentrations. At essentially non-toxic concentrations, SaliPhe protected 62.5% of mice against a lethal challenge of a mouse-adapted influenza strain, while BafA at cytotoxic concentrations showed essentially no protection against infection with IAV (SaliPhe vs. BafA P < 0.001).

CONCLUSIONS AND IMPLICATIONS

Our results show that a distinct binding site of the proton translocation domain of cellular v-ATPase can be selectively targeted by a new generation v-ATPase inhibitor with reduced toxicity to treat influenza virus infections, including multi-resistant strains. Treatment strategies against influenza that target host cellular proteins are expected to be more resistant to virus mutations than drugs blocking viral proteins.

The influenza pandemic of 2009: lessons and implications

Influenza is a moving target, which evolves in unexpected directions and is recurrent annually. The 2009 influenza A/H1N1 pandemic virus was unlike the 2009 seasonal virus strains and originated in pigs prior to infecting humans. Three strains of viruses gave rise to the pandemic virus by antigenic shift, reassortment, and recombination, which occurred in pigs as 'mixing vessels'. The three strains of viruses had originally been derived from birds, pigs, and humans. The influenza hemagglutinin (HA) and neuraminidase (NA) external proteins are used to categorize and group influenza viruses. The internal proteins (PB1, PB1-F2, PB2, PA, NP, M, and NS) are involved in the pathogenesis of influenza infection. A major difference between the 1918 and 2009 pandemic viruses is the lack of the pathogenic protein PB1-F2 in the 2009 pandemic strains, which was present in the more virulent 1918 pandemic strains. We provide an overview of influenza infection since 1847 and the advent of influenza vaccination since 1944. Vaccines and chemotherapy help reduce the spread of influenza, reduce morbidity and mortality, and are utilized by the global rapid-response organizations associated with the WHO. Immediate identification of impending epidemic and pandemic strains, as well as sustained vigilance and collaboration, demonstrate continued success in combating influenza.

Oseltamivir-resistant influenza A(H1N1) viruses in south of France, 2007/2009

Influenza A(H1N1) viruses resistant to oseltamivir carboxylate (OC) emerged in 2007/2008 in the absence of antiviral pressure. These OC-resistant A(H1N1) viruses had a better fitness than the sensitive ones as they were 100% prevalent in 2008/2009. To better understand the role of the neuraminidase (NA) affinity in the emergence of these OC-resistant A(H1N1) viruses we compared the NA properties among A(H1N1) clinical isolates in south of France between 2005 and 2009 and reference strains from 1977 to 2007, using NA inhibition assays, kinetic analyses of NA activities, and sequence analysis of viral NA and hemagglutinin (HA). In 2007/2008, among 374 A(H1N1) isolates tested, 38% were resistant to OC with a mean IC50 of 564+/-357 nM. The mean Km of OC-sensitive isolates (H275) was significantly lower (22.6+/- 4.7 microM) than the Km of previous reference strains (44.9+/- 5 microM) and the mean Km of the OC-resistant isolates (Y275) (37.2 +/- 7.7 microM). The combination of different amino acid mutations in N1 particularly the D344N could explain the higher NA affinity of A/Brisbane/59/2007 related variants compared to the previous A(H1N1) strains and the H275Y mutation allowed to retrieve Km values near 40 microM.

Assessing the viral fitness of oseltamivir-resistant influenza viruses in ferrets, using a competitive-mixtures model

To determine the relative fitness of oseltamivir-resistant strains compared to susceptible wild-type viruses, we combined mathematical modeling and statistical techniques with a novel in vivo "competitive-mixtures" experimental model. Ferrets were coinfected with either pure populations (100% susceptible wild-type or 100% oseltamivir-resistant mutant virus) or mixed populations of wild-type and oseltamivir-resistant influenza viruses (80%:20%, 50%:50%, and 20%:80%) at equivalent infectivity titers, and the changes in the relative proportions of those two viruses were monitored over the course of the infection during within-host and over host-to-host transmission events in a ferret contact model. Coinfection of ferrets with mixtures of an oseltamivir-resistant R292K mutant A(H3N2) virus and a R292 oseltamivir-susceptible wild-type virus demonstrated that the R292K mutant virus was rapidly outgrown by the R292 wild-type virus in artificially infected donor ferrets and did not transmit to any of the recipient ferrets. The competitive-mixtures model was also used to investigate the fitness of the seasonal A(H1N1) oseltamivir-resistant H274Y mutant and showed that within infected ferrets the H274Y mutant virus was marginally outgrown by the wild-type strain but demonstrated equivalent transmissibility between ferrets. This novel in vivo experimental method and accompanying mathematical analysis provide greater insight into the relative fitness, both within the host and between hosts, of two different influenza virus strains compared to more traditional methods that infect ferrets with only pure populations of viruses. Our statistical inferences are essential for the development of the next generation of mathematical models of the emergence and spread of oseltamivir-resistant influenza in human populations.

Oseltamivir resistance and the H274Y neuraminidase mutation in seasonal, pandemic and highly pathogenic influenza viruses

Along with influenza vaccines, the world is currently almost completely dependent on two licensed drugs for the treatment or prevention of seasonal (influenza A and B viruses) and pandemic influenza (influenza A viruses). These drugs - oseltamivir (Tamiflu) and zanamivir (Relenza) - are classified as neuraminidase inhibitors (NAIs) because they act by inhibiting one of the key surface proteins of the influenza virus, the neuraminidase, which in turn reduces the ability of the virus to infect other respiratory cells. Our dependence on these drugs has arisen because of high levels of resistance with seasonal influenza viruses to the older class of anti-influenza drugs, the adamantanes (amantadine and rimantadine), combined with the lack of activity of these drugs against influenza B viruses. Recently, however, significant levels of oseltamivir-resistant influenza A(H1) seasonal influenza viruses have also been encountered, which has been associated with a single amino acid change in the viral neuraminidase (H274Y). Oseltamivir is the most widely used and stockpiled NAI and, while these A(H1) viruses are still sensitive to zanamivir, it highlights the ease with which the influenza virus can mutate and reassort to circumvent available drugs. Fortunately, the current pandemic A(H1N1) 2009 virus, which is circulating globally, remains largely sensitive to both NAIs, although a small number of oseltamivir-resistant viruses have been isolated from patients to date, again with the H274Y mutation. Clearly there is a need to use the NAI drugs prudently to ensure they remain an effective defence against future seasonal and pandemic influenza viruses, along with careful monitoring of levels of resistance in the circulating viruses combined with the further development of new anti-influenza drugs.