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Drug-Resistant Avian Flu Virus Reported

The H5N1 avian flu virus has now spread from Asia to Europe. The virus is already a great threat to the world’s poultry industry, but the greater threat is that it will mutate, enabling easy infection and spread among humans. The only defenses against a new pandemic are immunization and antiviral treatment.

In vitro testing has shown that most H5N1 isolates are sensitive to the antiviral drug oseltamivir (Tamiflu). This has led many countries to stockpile the drug (for example, the U.K. has allocated funds to obtain enough to treat over 20% of its population). Flu viruses mutate readily, however, leading to concern that drug resistance could rapidly develop in an epidemic.

An international team reports that a 14-year-old Vietnamese girl infected with the H5N1 virus, and treated for 3 days with oseltamivir, developed resistance to the drug. Fortunately, the girl recovered. When ferrets were infected with the resistant virus, oseltamivir was ineffective. The oseltamivir-resistant strains of the virus were, however, easily killed by zanamivir (Relenza), in vitro and in the ferrets.

Comment: This report is discouraging, though not surprising. It calls into question the public-health value of investing in huge stockpiles of oseltamivir. Although the authors argue that their data suggest it might be useful to stockpile zanamivir, the data provide no reason to believe that resistance to that drug would not develop just as rapidly.

— Anthony L. Komaroff, MD

Published in Journal Watch General Medicine November 4, 2005

Citation(s):

Le QM et al. Isolation of drug-resistant H5N1 virus. Nature 2005 Oct 20; 437:1108.

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