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  • A perfect virus 'is a weak virus'

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Viruses need to make some mistakes when they reproduce in order to infect a person effectively, according to research carried out by a group of US researchers.

They suggest that their findings, published online by Nature this week (5 December), could lead to the development of a new class of antiviral drugs and vaccines to combat infections caused by a type of viruses known as RNA viruses.

RNA viruses cause diseases ranging from the common cold to hepatitis C and SARS.

The new drugs would force viruses to be more accurate which, ironically, would reduce their ability to reproduce and cause disease.

The research team, led by Raul Andino of the University of California, San Francisco, isolated a poliovirus that copies itself more accurately than the normal poliovirus, and found that it caused only mild infections.

The poliovirus was better at replicating itself because it had been bred in the presence of a powerful drug called ribavirin. This chemical usually creates so many errors during viral replication that the virus cannot survive.

To resist such a drug, as did the poliovirus in this study, a virus must maintain a very low error rate during replication.

But, since a low error rate makes the virus less potent, a drug like ribavirin could represent a new class of drugs against RNA viruses, Craig Cameron of Pennsylvania State University, an author of the study, told SciDev.Net.

The research also has implications for the development of vaccines against RNA viruses, Cameron added.

A vaccine must meet two requirements. Firstly, it must contain a virus that replicates successfully, but is weak enough not to cause disease.

Secondly, the virus must not be prone to mutations, or it might revert to a dangerous form.

The ribavirin-resistant poliovirus used in this study meets both criteria. It does not trigger severe disease symptoms, and it is forced to maintain a low mutation rate to conserve its ribavirin resistance.

Link to full abstract of paper in Nature

Reference: Nature doi:10.1038/nature04388 (2005)

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