Researchers have assembled a synthetic version of the polio virus in their lab using a recipe available on the Internet.

The virus was created using gene sequences obtained through the mail from a biotechnology firm. To test the virus, the researchers injected it into mice, which were paralysed and then killed.

The researchers say they did the experiment to show it can be done, and to warn people to take the threat of bioterrorism seriously.

Microbiologist Dr. Eckard Wimmer of the University of New York at Stony Brook led the research team and co-authored a study on the experiment, which appears in Friday's issue of the journal Science.

He said the process hasn't been used to produce a synthetic smallpox or other biological weapons threat, but given the pace of genetic research, it could be possible in 10 to 20 years.

Vaccination plans

The polio virus contains a simple genome that makes it relatively easy to build, scientists say. It also assembles itself directly from a DNA template, but the process is more complicated in other viruses.

The World Health Organization is working to eradicate polio, and doctors may stop inoculating people against the disease if it disappears from nature.

Wimmer recommends keeping all vaccines in storage indefinitely as a precaution, even for disease that have been eradicated.

The WHO plans to stockpile polio vaccines, and the U.S. government has arranged for anthrax and smallpox vaccines to be manufactured to protect its population.

The co-ordinator of WHO's polio eradication program, Bruce Aylward, told reporters the synthetic polio study is a significant research development. But he said the finding should not have major consequences for the WHO program.