More cases of Tamiflu resistant swine flu viruses have come to light, the World Health Organization said Wednesday.
China and Singapore have found Tamiflu-resistant pandemic viruses, Charles Penn, a scientist with the Geneva-based agency, said in an interview with The Canadian Press.
He revealed that the WHO has also been alerted informally to the discovery of a small number of other Tamiflu-resistant viruses. He would not say where they were found or how many there were in total.
"It's a small number. It certainly doesn't change the scale of what we're seeing," Penn said.
The WHO has received formal notification of seven cases where people suffering from pandemic flu were found to be infected with viruses resistant to Tamiflu, one of only two flu drugs that work against these H1N1 viruses. Since the time of their emergence earlier this year, the pandemic viruses have been resistant to two older flu drugs, amantadine and rimantadine.
Japan has reported finding three cases of resistance. Canada, Denmark, Hong Kong and Singapore have each found one.
Chinese authorities haven't yet filed a formal report including information about their case but WHO was alerted to the initial laboratory finding through the Global Influenza Surveillance Network, Penn said. The case occurred Hunan province.
Formal notification involves reporting on details of the case, including whether the patient was taking Tamiflu for treatment of flu or prophylaxis (prevention).
The WHO also wants to know whether the virus has been checked to see if all the genes are those of the pandemic virus or whether the pandemic virus might have swapped genes with the seasonal H1N1 virus.
That would be an unwelcome turn of events: virtually all the human H1N1 viruses circulating over the past year or so have been resistant to Tamiflu. It's an attribute public health authorities would not like to see the pandemic virus acquire.
Penn said to date there is no evidence of that kind of gene swapping - called reassortment. Nor is there any sign that the resistant pandemic H1 viruses are spreading from person to person, he said.
"Basically what it looks like is they are all individual isolated cases. No onward transmission and no suggestion or implication of them having originated, if you like, from a common source," he said.
It has always been expected that some degree of resistance to the drug would arise. Studies done years ago by the drug's maker, Roche, found that in rare cases people taking the drug either for treatment or prevention develop resistance.
"It's been there all the time as an event which can happen with a low frequency. And therefore what we're seeing now is no more or less than we would have expected from those early data," Penn said.
It was long thought Tamiflu-resistant flu viruses would not spread and so didn't pose much of a threat. But in the winter of 2008, the explosive development of resistance in seasonal H1N1 viruses showed the conventional wisdom was unfounded.
Laboratories around the world are on the lookout for changes in the pandemic viruses that might suggest a similar problem of resistance is emerging in them. But so far, no evidence has been found, Penn said.
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