There are viruses that kill bacteria.  The overwhelming majority of viruses do not affect our lives at all.

I found the story of viruses that kill bacteria most interesting.  Bacteriophages, or more commonly Phages, were used to treat bacterial infections from the time of WW1 until the discovery of antibiotics which were more effective.  Today, with so many bacteria becoming drug-resistant, researches are looking again at phages and finding ways to enhance their effectiveness.

"The Global Viral Forecasting Initiative is trying to change the way we fight viruses. Someday, somewhere, a virus we don’t know about is going to emerge as a major new threat to human health. We’ve seen it happen many times before, and so we know it will happen again. GVFI scientists think we’ll do a better job fighting that new virus if we can learn something about it in advance. To eliminate the advantage of surprise, GVFI scientists are looking for these viruses before they jump into humans. The best place to look for them is in animals, such as the monkeys."

"Viruses are the smallest living things known to science, and yet they hold the entire planet in their sway. Viruses have been a part of our lives for so long, in fact, that we are actually part virus: the human genome contains more DNA from viruses than our own genes. Meanwhile, scientists are discovering viruses everywhere they look: in the soil, in the ocean, even in deep caves miles underground. A Planet of Viruses explores how viruses regulate the biosphere, how they helped give rise to the first life-forms, how viruses are producing new diseases, how we can harness viruses for our own ends, and how viruses will continue to control our fate for years to come."

The essays in this book were written for the World of Viruses project at the University of Nebraska, funded by the National Center for Research Resources at the National Institutes of Health through the Science.

Carl Zimmer writes about science for the New York Times and other publications and is the author of eight books, including Parasite Rex, Soul Made Flesh, and Microcosm. He is a lecturer at Yale University, where he teaches writing about science and the environment, and visiting scholar at the Science, Health, and Environment Reporting Program at New York University’s Arthur L. Carter Journalism Institute.