Infectious disease experts announced Monday that seasonal flu viruses are growing resistant to antiviral drugs. While the problem is worldwide, Europe is the worst affected by the resistant viruses, they told a meeting of the Infectious Diseases Society of America.
“A significant proportion of resistant viruses were observed in Europe this winter,” Dr. Bruno Lina of Claude Bernard University in Lyons, France, told the audience.
The resistance varies by strain, with one in four H1N1 flu viruses resistant in Europe and about one in ten in the United States. There are far fewer cases of H3N2 and influenza B resistant viruses, the experts reported.
Already known to mutate rapidly, flu viruses may be even more unpredictable than previously believed, they said.
Health experts fear antiviral drugs may quickly become unable to combat a severe flu season or the appearance of a new strain, something that might result in a pandemic. They urge the need to develop new flu drugs, with better and faster methods to make vaccines.
The World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) have been gathering samples of the annual flu viruses to track them against the four available flu drugs: rimantadine, amantadine and the newer drugs Tamiflu and Relenza. Roche AG’s Tamiflu, known generically as oseltamivir, is a pill that can treat symptoms and also prevent infection.
But according to Lina, the viruses changed quickly over the past 2007-2008 flu season.
“We started with something like 10 percent in Europe,” he said, adding that in April of this year 25 percent of the viruses were Tamiflu-resistant.
“U.S. flu viruses developed a sudden ability to evade the effects of the older drugs amantadine and rimantadine during the 2005-2006 flu season,” Dr. Larisa Gubareva of the CDC told Reuters.
In fact, in 2006 the CDC said no one should use the drugs any more.
Experts were optimistic about two newer drugs ““ Tamiflu and GlaxoSmithKline’s Relenza, known generically as zanamivir ““ but resistance to Tamiflu is already being observed.
Lina’s team analyzed more than 2,600 samples of flu viruses from European patients, and found puzzling patterns of resistance that appeared to be unrelated to the actual use of Tamiflu.
For instance in Paris, more than half of those tested carried the mutation that would give resistance to Tamiflu, compared with only 29 percent in southeastern France.
“Which makes absolutely no sense,” said Lina, noting that patients exhibited no difference in symptoms whether infected with resistant virus or not.
“It’s difficult to understand. I have no idea why these viruses emerged,” he said.
In Europe, the most resistant viruses were the H1N1.
Gubareva said tests across the U.S., Canada and Mexico showed very rapid development of drug resistance among H1N1 viruses. As of May 15, resistant viruses had been detected in 18 out of the 43 U.S. states where virus samples were tested, she said. In Canada, resistant viruses were found in nine of 13 provinces. However, only 6 percent of H3N2 and influenza B samples tested in the three countries showed the genetic mutations for Tamiflu resistance, she said.
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