SCIENTISTS DESIGN DEADLY SUPERVIRUS.(MAIN)

Byline: WILLIAM J. BROAD New York Times

Scientists have created a highly lethal virus in an effort to develop stronger protections against the threat of supervirulent forms of smallpox that terrorists might turn on humans, researchers said on Friday.

The genetic engineering involved a virus known as mousepox, which infects mice but is not known to hurt people. Into that virus, a cousin of the smallpox virus, the scientists spliced a single gene that made it superlethal. They tested it on mice that had been treated with different combinations of a smallpox vaccine and drugs.

The scientists said the experimental results showed that the best defenses …