[Source: EurekAlert, full text: (LINK). Extract.]
H7N9 influenza strain resistant to antivirals, but tests fail to identify resistance
Some strains of the avian H7N9 influenza that emerged in China this year have developed resistance to the only antiviral drugs available to treat the infection, but testing for antiviral resistance can give misleading results, helping hasten the spread of resistant strains. The authors of a study published in mBio®, the online open-access journal of the American Society for Microbiology, characterized viruses taken from the first person known to be stricken with H7N9 influenza and found that 35% of those viruses are resistant to oseltamivir (commercially known as Tamiflu) and zanamivir (Relenza), front line drugs used for treating H7N9 infections. However, lab testing of the viruses, which detects the activity of a viral enzyme, fails to detect that these strains are resistant, so monitoring for the development of resistance using this technique would prove futile. "If H7N9 does acquire human-to-human transmissibility, what do we have to treat it with until we have a vaccine? Oseltamivir. We would be in big trouble," says corresponding author Robert Webster of St. Jude Children's Research Hospital in Memphis, Tennessee. Resistant strains of H7N9 can flourish in patients treated with oseltamivir or zanamivir, he says, inadvertently leading to the spread of resistant infections.