It's an incurable virus, as deadly as Ebola and as contagious as measles. Scientist call it "Virus X" - will it be the next plague? In this hour of To the Best of Our Knowledge, the human battle against the microbe. Also virologists who tread where others wouldn't dare -- into the "hot zone."

SEGMENT 1

Physician Frank Ryan tells Jim Fleming that "Virus X" is a worst case scenario that could threaten the human race and explains how viruses operate in symbiosis with their hosts. Ryan is the author of "Virus X: Tracking the New Killer Plagues."

SEGMENT 2:

Virologists Joseph McCormick and Susan Fisher-Hoch, formerly with the Centers for Disease Control, tell Steve Paulson about their work in the lab and in the field with the world's deadliest viruses. They are co-authors of "Level 4: Virus Hunters of the CDC." Also, Christopher Wills tells Steve Paulson that most of today's disease organisms have been around for a long time and have altered human history on various occasions. Wills teaches biology at the University of California - San Diego and is the author of "Yellor Fever, Black Goddess: The Co-evolution of People and Plagues."

SEGMENT 3:

Evolutionary biologist Richard Dawkins has coined the word "meme" to describe a thought or set of thoughts that propagate like a virus. Dawkins tells Judith Strasser than memes range from the fashion for wearing baseball caps backwards to organized religion. Dawkins teaches at Oxford and is the author of "Climbing Mount Improbable."

Distribution dates:

• week of 02/09/97 - hour 2
• week of 01/04/98 - hour 2