28 October, 2008
Global Spread of Oseltamivir (Tamiflu)-Resistant Human Influenza A
(H1N1)
The World Health Organization (WHO) on 14 October
updated on their influenza website the global tracking of “Influenza A (H1N1)
virus resistance to oseltamivir---2008 influenza season”. The results show that
such resistance is continuing to spread globally, including in the southern
hemisphere during the recent flu season.
From the second quarter of 2008 until 13 October 2008
an illustrative selection of nations from the WHO report demonstrates:
|
Country |
Number (%) of resistant isolates |
|
|
|
|
South Africa |
225/225 (100%) |
|
Senegal |
10/10 (100%) |
|
Ghana |
5/13 (38%) |
|
|
|
|
Argentina |
15/33 (45%) |
|
Chile |
10/79 (13%) |
|
Uruguay |
13/16 (81%) |
|
|
|
|
Australia |
47/59 (80%) |
|
Philippines |
10/11 (91%) |
|
Hong Kong SAR |
97/583 (17%) |
|
|
|
|
Japan |
0/61 (0%) |
|
Brazil |
0/12 (0%) |
|
Thailand |
0/12 (0%) |
The neuraminidase mutation that has been found
responsible for this oseltamivir resistance is the H274Y histamine to tyrosine
mutation. Only rarely have any of the
patients with this human H1N1 flu virus mutation been exposed to oseltamivir
(Tamiflu). The reason for the occurrence
of these oseltamivir-resistant viruses is still unknown.
Of note, however, these viruses are clearly
transmitted from person-to-person. Previously, oseltamivir-resistant influenza
viruses were generally thought to be
“less-fit”, and thus unable to be transmitted readily from person-to-person in
a sustained manner as is being seen now both in the southern and northern
hemispheres during their respective influenza seasons in 2008.
These oseltamivir resistant viruses remain susceptible
to the (inhaled) neuraminidase inhibitor drug “zanamivir” (Relenza).
The advent of the flu season in the northern
hemisphere now can be predicted to bring with it increased resistance to
oseltamivir among influenza A (H1N1) viruses.
Whether this resistance pattern expands to include human influenza A
(H3N2) or avian influenza A (H5N1) warrants close surveillance world-wide,
including from nations near the equator that can have year-round influenza
virus transmission.
Daniel R. Lucey, MD, MPH
EROne Institutes, Department of Emergency Medicine
Washington Hospital Center
Adjunct Professor of Microbiology and Immunology
Georgetown University Medical Center
Washington, D.C.
Website for this newsletter: www.BePast.org
Email:
DRL23@Georgetown.edu