Many viruses can exist inside a host for long periods during which little damage is done.

The virus could not possibly have existed on this world much longer than humanity.

A virus may just have been identified, but similar viruses may exist.

The virus heretofore designated Catalyst, it stated, did not exist.

Although Windows is by far the most popular target operating system for virus writers, viruses also exist on other platforms.

Continuing research with the current stocks is necessary because the virus does not exist in a natural state, he said.

And this was a time before we knew that viruses existed.

This indicates that viruses emerged early in the evolution of life and existed before modern cells.

We know that the virus has existed in the United States since at least the mid- to late 1970s.

We'll decide, when the virus exists, whether or not to use it.