But so far, this particular virus hasn't changed much since it first appeared.

"These particular viruses have been with us a long time," Kaye said.

We're all concentrating too strongly on this particular virus, however.

"Why would a particular virus be transmitted easily human to human, and another not?"

It, too, gave no hint why this particular virus was so deadly.

A vaccine against a particular virus is relatively easy to create.

Sometimes, only one species is the principal carrier of a particular virus.

Once exposed to a particular virus, the instructor had explained, you became immune to it.

But there is, experts said, no way to predict exactly when or whether a particular virus will become an imminent threat.

That particular virus, however, turned out not to be a threat.