Widespread Use Of Tamiflu May Help H5N1 Become More Deadly, Infectious

The short version : Tamiflu passes through humans and into sewerage and water systems. Scientists are now concerned that Tamiflu could then leach back into areas where migrating birds sometimes gather and give the H5N1 virus more opportunity to meet its 'front line attacker' and learn how to beat it.

From news.com.au :

Tamiflu - the frontline weapon in any bird-flu pandemic - cannot be broken down by sewage systems and could help the virus mutate dangerously into a drug-resistant strain, Swedish scientists say.

Scientists led by Jerker Fick, a chemist at Umea University, tested the survivability of the Tamiflu molecule in water drawn from three phases in a typical sewage system.

The first was raw sewage water; the second was water that had been filtered and treated with chemicals; the third was water from "activated sludge," in which microbes are used to digest waste material.

Tamiflu's active ingredient survived all three processes, which means that it is released in the waste water leaving the plant.

The finding is important because of the risk that Tamiflu, if overprescribed, could end up in the wild in concentrations high enough to let H5N1 adapt to this key drug, the authors say.

Flu viruses are common among waterfowl, especially dabbling ducks such as mallards which often forage for food near sewage outlets.

"The biggest threat is that resistance will become common among low pathogenic influenza viruses carried by wild ducks," said co-author Bjoern Olsen, professor of infectious diseases at the University of Uppsala and University of Kalmar.

These avian viruses could then recombinate with ordinary human flu viruses, creating new strains that are resistant to Tamiflu, he said.

The story also includes interesting use from Japan about the long-term effects of using Tamiflu to fight the yearly round of influenza outbreaks. During the 2004-2005 influenza 'season' in Japan some 16 million fell ill. Six million were treated with Tamiflu.

The Japanese are now showing some of the highest rates of an "emerging resistance" to Tamiflu anywhere in the world.