May 28, 2013 at 11:28 AM ET
The new H7N9 bird flu strain that has killed 36 people in China has developed resistance to antiviral drugs, Chinese researchers said Tuesday.
The mutation has developed especially quickly, and scientists said they were concerned, although influenza viruses usually do evolve into forms that can resist the effects of antiviral drugs.
"The apparent ease with which antiviral resistance emerges in A/H7N9 viruses is concerning; it needs to be closely monitored and considered in future pandemic response plans," Dr. Zhenghong Yuang of the Shanghai Public Health Clinical Center and colleagues wrote in a paper published online by The Lancet medical journal on Tuesday.
Tamiflu is a pill in a class of drugs called neuraminidase inhibitors. They currently offer the only known treatment option for bird flu. GlaxoSmithKline's inhaled medicine Relenza is the the same class of drugs.
None of the drugs cures the infection. But if given withing a day or two of symptoms starting, they can make the illness less severe and perhaps cut a day or two off the time to recovery.
Yuang's team tested 14 patients with severe H7N9 infections. Most were helped by Tamiflu. But three were not, and in one of those three patients, the gene mutation responsible for resistance appears to have arisen after he was treated with Tamiflu. That suggests the giving Tamiflu can quickly push the virus into mutations that resist its effects.
It's also possible, they said, that giving patients steroids helped drive the mutation.
It’s not unexpected. Flu viruses mutate constantly and quickly and most strains of flu develop resistance to drugs sooner or later. The two older flu drugs amatadine and rimantadine are virtually useless against seasonal flu.
Yuang's team also found bits of H7N9 virus in the patients' throats, blood, stools and urine. It is possible that this means the virus can spread in various routes -- not just through the usual mode of respiratory secretions, they said. This possibility needs more study, they noted.
The H7N9 virus is known to have infected 131 people in China since February, but no new cases have been detected since early May, according to the World Health Organization.
Experts from the United Nations agency said last week the bird flu outbreak in China had caused $6.5 billion in losses to the economy.