lunes, 15 de marzo de 2010

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




EID Journal Home > Volume 16, Number 3–March 2010

Volume 16, Number 3–March 2010
Dispatch
Rare Influenza A (H3N2) Variants with Reduced Sensitivity to Antiviral Drugs
Clyde Dapat,1 Yasushi Suzuki,1 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); and Central Myanmar Department of Medical Research, Nay Pyi Taw, Myanmar (Y.Y. Myint, N. Lin, H.N. Oo)


Suggested citation for this article

Abstract
In 2007 and 2008 in Myanmar, we detected influenza viruses A (H3N2) that exhibited reduced sensitivity to both zanamivir and amantadine. These rare and naturally occurring viruses harbored a novel Q136K mutation in neuraminidase and S31N mutation in M2.

Adamantanes and neuraminidase inhibitors (NAIs) are the 2 classes of drugs indicated for preventing or treating influenza virus infection. In 2005, the high prevalence of influenza viruses A (H3N2) with S31N mutation in M2 limited the effectiveness of amantadine (1,2). In 2008, the emergence of subtype H1N1 with H274Y mutation in neuraminidase (NA) raised concerns about the use of oseltamivir (3,4). On the other hand, the incidence of zanamivir-resistant viruses was low (5). In 1998, 1 case of zanamivir-resistant influenza B virus, which was isolated from an immunocompromised child who underwent prolonged zanamivir treatment, was reported (6). In 2008, subtype H3N2 with D151A/V mutations in NA demonstrated reduced zanamivir sensitivity by chemiluminescent NAI assay (5). Recently, zanamivir-resistant subtype H1N1 isolates with a novel Q136K mutation in NA were isolated in Oceania and Southeast Asia (7).

We report the detection of influenza viruses A (H3N2) harboring a Q136K mutation in NA and an S31N mutation in M2, which respectively confer reductions in zanamivir and amantadine susceptibility. In 2007 and 2008, we performed phenotypic and genotypic analyses in characterizing these viruses from Myanmar.

The Study
Nasopharyngeal swabs were collected from patients with influenza-like illness at Sanpya Hospital in Yangon, Myanmar, and outpatient clinics affiliated with the Department of Medical Research (Central Myanmar) in Nay Pyi Taw. Rapid test kit–positive samples were sent to Niigata University, Japan, for subsequent analyses. Virus isolation and subtyping PCR were performed as previously described (8). The NAI susceptibility test was performed by a fluorescence-based NA activity assay that measures the 50% inhibitory concentration (IC50) by using zanamivir and oseltamivir carboxylate (9). All samples were assayed in duplicates in >2 independent experiments. A sample was considered an extreme outlier if its IC50 value was 10´ higher than the mean values for sensitive strains with >3 interquartile range from the 25th and 75th percentiles in the box-and-whisker plot analysis (9). So far, all known NAI-resistant viruses are extreme outliers (10). Screening for S31N mutation in M2 was done by cycling probe real-time PCR (11). Sequencing and phylogenetic analysis of the hemagglutinin (HA) and NA genes were performed as previously described (8).

A total of 253 and 802 rapid test kit–positive samples were collected in Myanmar in 2007 and 2008, respectively. Of these, 64 isolates of subtype H3N2 were detected in 2007 and 211 in 2008. NAI susceptibility assay showed 1 (1.5%) isolate (A/Myanmar/M187/2007) with a zanamivir IC50 value of 59.72 nM, which was collected in August 2007, and 1 (0.5%) isolate (A/Myanmar/M114/2008) with a zanamivir IC50 of 33.37 nM, which was collected in July 2008. These isolates respectively demonstrated a 53´ and 30´ reduction in zanamivir susceptibility (Table) and were extreme outliers (data not shown). On the basis of cycling probe real-time PCR assay, these viruses had an S31N mutation in M2, which confers resistance to amantadine. All subtype H3N2 viruses analyzed in this study remain sensitive to oseltamivir carboxylate (Table).

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http://www.cdc.gov/eid/content/16/3/493.htm

Suggested Citation for this Article
Dapat C, Suzuki Y, Saito R, Kyaw Y, Myint YY, Lin N, et al. Rare influenza A (H3N2) variants with reduced sensitivity to antiviral drugs. Emerg Infect Dis [serial on the Internet]. 2010 March [date cited]
. http://www.cdc.gov/EID/content/16/3/493.htm

DOI: 10.3201/eid1603.091321

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