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Antimicrobial Agents and Chemotherapy, November 2006, p. 3809-3815, Vol. 50, No. 11
0066-4804/06/$08.00+0     doi:10.1128/AAC.00645-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Natural Variation Can Significantly Alter the Sensitivity of Influenza A (H5N1) Viruses to Oseltamivir{triangledown}

M. A. Rameix-Welti,1 F. Agou,2 P. Buchy,3 S. Mardy,3 J. T. Aubin,1 M. Véron,2 S. van der Werf,1,4 and N. Naffakh1*

Unité de Génétique Moléculaire des Virus Respiratoires, URA CNRS 1966,1 Unité de Régulation Enzymatique des Activités Cellulaires, URA CNRS 2185, Institut Pasteur, Paris, France,2 Institut Pasteur du Cambodge, Phnom Penh, Cambodia,3 EA302, Université Paris 7, Paris, France4

Received 26 May 2006/ Returned for modification 7 July 2006/ Accepted 17 August 2006

Geographic spread of highly pathogenic avian H5N1 influenza viruses may give rise to an influenza pandemic. During the first months of a pandemic, control measures would rely mainly on antiviral drugs, such as the neuraminidase (NA) inhibitors oseltamivir and zanamivir. In this study, we compare the sensitivities to oseltamivir of the NAs of several highly pathogenic H5N1 viruses isolated in Asia from 1997 to 2005. The corresponding 50% inhibitory concentrations were determined using a standard in vitro NA inhibition assay. The Km for the substrate and the affinity for the inhibitor (Ki) of NA were determined for a 1997 and a 2005 virus, using an NA inhibition assay on cells transiently expressing the viral enzyme. Our data show that the sensitivities of the NAs of H5N1 viruses isolated in 2004 and 2005 to oseltamivir are about 10-fold higher than those of earlier H5N1 viruses or currently circulating H1N1 viruses. Three-dimensional modeling of the N1 protein predicted that Glu248Gly and Tyr252His changes could account for increased sensitivity. Our data indicate that genetic variation in the absence of any drug-selective pressure may result in significant variations in sensitivity to anti-NA drugs. Although the clinical relevance of a 10-fold increase in the sensitivity of NA to oseltamivir needs to be investigated further, the possibility that sensitivity to anti-NA drugs could increase (or possibly decrease) significantly, even in the absence of treatment, underscores the need for continuous evaluation of the impact of genetic drift on this parameter, especially for influenza viruses with pandemic potential.

* Corresponding author. Mailing address: Unité de Génétique Moléculaire des Virus Respiratoires, URA CNRS 1966, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France. Phone: 33-1-45 68 88 11. Fax: 33-1-40 61 32 41. E-mail: nnaffakh{at}pasteur.fr.

{triangledown} Published ahead of print on 28 August 2006.

Antimicrobial Agents and Chemotherapy, November 2006, p. 3809-3815, Vol. 50, No. 11
0066-4804/06/$08.00+0     doi:10.1128/AAC.00645-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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