Flu Showing Signs Of Resistance To Antivirals

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Main Category: Flu / Cold / SARS
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Article Date: 04 Apr 2007 - 1:00 PDT


The flu virus is starting to show signs of resistance to commonly used antivirals.

A new research study in Japan suggests that Influenza B is becoming resistant to two antivirals commonly used to protect against flu, zanamivir (brand name Relenza) and oseltamivir (Tamiflu). These are both neuraminidase inhibitor drug types.

Studies have already shown that Influenza A is becoming resistant to oseltamivir (Tamiflu), but this is the first documented evidence of Influenza B starting to do the same. Influenza B is the flu virus that is said to cause annual flu outbreaks.

The study is published in the Journal of the American Medical Association (JAMA) and was conducted in Japan by Dr Shuji Hatakeyama, of the University of Tokyo, and scientists from various academic and government institutes.

Dr Hatakeyama and colleagues took before and after samples from 74 children who were treated with oseltamivir (Tamiflu) in the 2004-2005 Type B flu epidemic in Japan and also from 348 other patients (including 66 adults) who were not treated. The patients were seen at 4 different community hospitals.

They found:

-- One child of the 74 (1.4 per cent) who had been treated with oseltamivir (Tamiflu) had a variant of flu virus with reduced drug sensitivity.
-- Variants with reduced sensitivity in 7 (1.7 per cent) of 422 viruses from the 348 untreated patients.
-- Of the 7 patients with resistant flu strains, 4 had acquired their infection in the community, and 3 had probably been infected by siblings shedding the mutant strains.

The researchers concluded that in the population they studied, Influenza type B with reduced sensitivity to these types of drugs do not arise as frequently as type A resistant strains.

"However, they appear to be transmitted within communities and families, requiring continued close monitoring," they added.

An editorial accompanying the article says that preparations for epidemics and pandemics have so far been ignoring the possibility that flu will become resistant to neuraminidase inhibitors because until now there has been no evidence on which to estimate the medical consequences.

And another commentary in Journal Watch, another JAMA publication, suggests that while this study shows a low level of resistance in the Influenza B virus compared with Influenza A (5-18 per cent) and only speculates about transmissibility, the findings "are worrisome and deserve follow-up".

Experts have been worried for some time about the overuse of antivirals to fight the flu virus. They say the drugs are administered incorrectly - being given just in case a person is exposed to flu instead of when they are in contact with infected people.

Influenza is a respiratory infection caused by an RNA-based virus that infects birds, humans and other mammals. In humans the symptoms tend to be high temperature, sore throat, pains in the muscles, severe headache, cough, and feeling fragile and tired. In serious cases it can lead to pneumonia and death in children and older people.

There are three types of influenza: A, B and C.

-- Type A is the most common and usually causes the most serious epidemics. It mutates at a higher rate than the other two. The Spanish Flu and Avian Flu are Type A.
-- Type B can also can cause epidemics, but the disease is milder than type A. The virus mutates more slowly than type A.
-- Type C viruses have never caused a large epidemic.

Antiviral drugs like oseltamivir (Tamiflu) and zanamivir (Relenza) are from a group known as neuraminidase inhibitors. They halt the spread of the flu virus in the body and are use to treat both Influenza A and B.

Patients wondering how this news affects their annual flu shots are reminded that the annual flu shot is a vaccine. This research is about antivirals. A vaccine is different, it stimulates the body's immune system to produce its own antibodies to fight the virus.

"Emergence of Influenza B Viruses With Reduced Sensitivity to Neuraminidase Inhibitors."
Shuji Hatakeyama; Norio Sugaya; Mutsumi Ito; Masahiko Yamazaki; Masataka Ichikawa; Kazuhiro Kimura; Maki Kiso; Hideaki Shimizu; Chiharu Kawakami; Kazuhiko Koike; Keiko Mitamura; Yoshihiro Kawaoka.
JAMA. 2007;297:1435-1442.
Vol. 297 No. 13, April 4, 2007

Click here for Abstract.

click here for Flu Fact Sheet from National Institute of Allergy and Infectious Diseases (US).

Written by: Catharine Paddock
Writer: Medical News Today


Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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