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Volume 16, Number 3—March 2010


Rare Influenza A (H3N2) Variants with Reduced Sensitivity to Antiviral Drugs

Clyde Dapat1Comments to Author , Yasushi Suzuki1, Reiko Saito, Yadanar Kyaw, Yi Yi Myint, Nay Lin, Htun Naing Oo, Khin Yi Oo, Ne Win, Makoto Naito, Go Hasegawa, Isolde C. Dapat, Hassan Zaraket, Tatiana Baranovich, Makoto Nishikawa, Takehiko Saito, and Hiroshi Suzuki
Author affiliations: Niigata University, Niigata, Japan (C. Dapat, Y. Suzuki, R. Saito, M. Naito, G. Hasegawa, I.C. Dapat, H. Zaraket, T. Baranovich, H. Suzuki); National Institute of Animal Health, Tsukuba City, Japan (T. Saito); Niigata Prefectural Institute of Public Health and Environmental Sciences, Niigata (M. Nishikawa); Sanpya Hospital, Yangon, Myanmar (Y. Kyaw); National Health Laboratory, Yangon (K.Y. Oo, N. Win); Central Myanmar Department of Medical Research, Nay Pyi Taw, Myanmar (Y.Y. Myint, N. Lin, H.N. Oo)

Main Article


Characteristics of subtype H3N2 influenza viruses with Q136K mutation in NA and S31N substitution in M2*

Strains Passage history NA mutation IC50s of NA inhibitors
Amantadine sensitivity† (M2 mutation)
nM ± SD Fold change Oseltamivir, nM ± SD Fold change
All NAI-sensitive subtype H3N2 isolates‡ MDCK2 None 1.12 ± 0.40 1 0.86 ± 0.44 1 Resistant (S31N)
A/Myanmar/M187/2007 MDCK2 Q136K 59.72 ± 3.83 53.3 0.13 ± 0.05 0.2 Resistant (S31N)
A/Myanmar/M114/2008 MDCK2 Q136K 33.37 ± 7.02 29.8 0.16 ± 0.03 0.2 Resistant (S31N)
A/Texas/131/2002§ None 1.43 ± 0.09 1.3 0.99 ± 0.09 1.2 Sensitive
A/Texas/131/2002_E119V§ E119V 5.43 ± 0.68 4.8 94.33 ± 2.06 109.7 Sensitive

*NA, neuraminidase;IC50, inhibitory concentration; NAI, neuraminidase inhibitors.
†Amantadine sensitivity was based on M2 genotyping data.
‡Average IC50 was calculated excluding the control viruses (n = 47).
§Reference strains used as drug-sensitive and -resistant control viruses in the NAI assay.

Main Article

1These authors contributed equally to this article.