The feat proves that even if all the polio virus in the world were destroyed, it would be easily possible to resurrect the crippling disease, says Aniko Paul at the State University of New York at Stony Brook, one of the researchers conducting the study.

The result has major implications for vaccination programs that have nearly rid the world of polio. "I think it means you're probably not going to be able to stop vaccinating people even after you eradicate the virus," says Diane Griffin of the Johns Hopkins Bloomberg School of Public Health.

Paul believes the synthesis method could be applied to other viral diseases. "We feel this could be used for ebola, smallpox, just about anything," she says. This raises the worrying possibility that bioterrorists could use a similar approach to create devastating diseases without having to gain access to protected viral stocks.

However, infectious disease specialists emphasise that these other viruses are far more complex than poliovirus and, for the time being at least, could not be synthesised so easily.

Step by step
 

Much of the technology needed for this experiment has been around for more than a decade, so researchers expected the experiment to work. "Conceptually, it's not a surprise," says Eric Rubin from Harvard's School of Public Health.

Nonetheless, it is the first time that researchers have generated an infectious agent from scratch. Paul says: "It's important that the scientific world knows that this is possible. If we know about it, we can prepare for it."

Paul and her colleagues used chemical techniques to produce large segments of DNA corresponding to portions of the polio virus. They made one segment themselves, then ordered the rest from a company that routinely machine-generates DNA.

Once they had all the segments, the team pasted the pieces together to produce one long stretch of DNA. They then used a commercially available enzyme to convert the DNA into RNA - the genetic form of the polio virus.

Finally, they added the RNA to a soup made from human cells. This enabled the RNA to use the cellular machinery to create the proteins that complete the virus particles. The result was an infectious agent that could destroy cultured human cells and paralyse or kill mice in much the same way as the normal polio virus.

Journal reference: Science (DOI: 10.1126/science.1072266)

Robin Orwant

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