Flu-Drug Use Could Promote Virus Resistance, Study Finds

Kate Ravilious
for National Geographic News
April 20, 2006
Facing the potential threat of a global bird flu pandemic, many governments are stockpiling antiviral drugs such as Tamiflu. These drugs are known to help infected patients recover, and they can slow the spread of a virus if they are given to people who aren't infected.

But research shows that widespread use of such medications can promote virus mutation, increasing the probability of new strains developing and making it harder to stamp out a virus in the long run.

This provides a serious dilemma: Should antiviral drugs be given out sparingly, leaving many people exposed and in danger? Or should the tablets be dispensed widely, despite the enhanced risk of resistant strains of flu emerging?

Roland Regoes and Sebastian Bonhoeffer of the Swiss Federal Institute of Technology Zurich are helping to answer these kinds of questions using mathematical models of infectious disease.

By simplifying the situation and considering a small enclosed population, such as five hundred people in a boarding school, they are able to focus on how a virus evolves.

Specifically, the researchers have been studying the effect of the drugs during a pandemic.

(See maps of a simulated flu outbreak in the United States, showing rates of infection if antiviral drugs are administered and if they are not.)

"During a pandemic we will have a tremendous problem developing a vaccine, so antiviral drugs will be our first line of defense," Bonhoeffer said.

However, dispensing the antiviral drugs too freely could also make the problem worse.

No Data From the Past

Antiviral drugs are a relatively new development. The last time there was a flu pandemic, these drugs didn't exist and people just had to suffer through the virus.

If a pandemic strikes again, antivirals are likely to be a key weapon, but it is vital that they are used optimally, experts warn.

In a paper in the journal Science, Regoes and Bonhoeffer describe the outcomes from two model scenarios. In one scenario, only people showing virus symptoms are given antiviral drugs. In the other case, all people who may have been exposed to the virus are given the medication.

The researchers found that the less the drugs are used, the lower the chances of a resistant strain of a virus emerging.

"If you hit a large proportion of the population, then the selection pressure on the virus to form mutations is quite high," Bonhoeffer explained.

Weighing the Risks

Nonetheless, Regoes and Bonhoeffer believe that antiviral drugs are still very important if a viral pandemic occurs.

"This doesn't mean that we should refrain from using them, but that we need to be more prepared for the development of resistant transmissible viruses, a risk that has perhaps been previously downplayed," Bonhoeffer said.

The new findings are backed up by instances in which antiviral drugs have been used extensively to tackle diseases like malaria and HIV.

"Usually, resistant strains come, with a certain time delay, but they still come. That is the sad reality," Bonhoeffer said.

The scientists stress that before their results can be used for public health planning, they need to do more large-scale models that take into account some of the complexities of the real world.

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