Viruses have a bad connotation.  We immediately think of the ones that cause disease: “I’ve got a virus,” you say when feeling under the weather.  Actually, you have trillions of them all the time, even in the best of health.  A single gram of stool sample can have 10 billion of them!  What does that mean?  Scientists are only beginning to find out.

One thing it means is that they can’t be all bad.  Elizabeth Pennisi reported in Science this week about work at the University of British Columbia and Washington University to explore the human virome.1  She began her report,

In the past decade, scientists have come to appreciate the vast bacterial world inside the human body.  They have learned that it plays a role in regulating the energy we take in from food, primes the immune system, and performs a variety of other functions that help maintain our health.  Now, researchers are gaining similar respect for the viruses we carry around.

Bacteria have been easier to count than the tiny viruses.  Many of our internal viruses are bacteriophages that invade and kill bacteria.  This suggests they play a role in keeping the brakes on bacterial infections.  “For every bacterium in our body, there’s probably 100 phages,” Pennisi wrote.  The number of virus species identified in stool samples of healthy adults varied from 52 to 2773.  “The viromes varied significantly from one individual to the next; they were even more diverse than the bacterial communities within the same individuals,” Pennisi reported.  “But each person’s viral community remained stable over the course of the year.”  That is, unless they go on a different diet or eating regimen; then the viromes change.  But people who eat the same foods tend to converge on virus profiles.  Researchers also found that infants with fevers had more viruses than healthy infants….

 

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