The fact that a person is healthy does not mean that he is free of viruses.
According to a new study, the same viruses that make us sick can take up residence in the human body without causing a sneeze, cough, or other symptoms.
On average, healthy people harbor about five types of viruses in their bodies, according to researchers at the Washington University School of Medicine in St. Louis.
The study is the first comprehensive analysis to describe the diversity of viruses in healthy people.
«Most everyone is familiar with the idea that there is a normal bacterial flora in the body,» said study co-author Gregory Storch, a virologist and chief of the Division of Pediatric Infectious Diseases.
«Many people wondered if something similar happens with viruses, but so far they do not impose a clear answer. We now know that there is a normal, rich and complex viral flora.»
The researchers swabbed 102 healthy young people between the ages of 18 and 40 from up to five parts of their bodies: nose, skin, mouth, feces, and vagina.
In 92% of the subjects at least one virus was detected, and some of the individuals have between 10 and 15 viruses.
«We are impressed by the number of viruses that we found,» said Kristine M. Wylie, a professor of pediatrics and lead author of the study.
«We only studied up to five body sites in each person and if we had looked at the whole body we would have found more.»
The scientists saw that each individual had a different viral fingerprint.
Researchers don’t yet know whether viruses have a positive or negative effect on overall health, but they speculate that in some cases, they may keep the immune system primed to respond to dangerous danger, while in others, persistent viruses increase the risk of disease.
Study volunteers were carefully screened to confirm that they were healthy and had no symptoms of acute infection.
Various types of viruses
The scientists found seven families of viruses, including strains of herpes viruses that are not sexually transmitted.
For example, herpesvirus 6 or 7 was found in 98% of individuals whose mouths were swabbed.
Certain strains of papillomavirus were found in approximately 75% of skin samples and 50% of samples from the nose.
Not surprisingly, the vagina is dominated by papillomaviruses.
38% of women showed to have these strains.
Some of the women harbored certain high-risk strains that increase the risk of cervical cancer.
Adenoviruses, the viruses that cause the common cold and pneumonia, are also common in many parts of the body.
And while experts acknowledge that more study is needed, they are pleased to have a clearer picture of the virus communities that inhabit healthy bodies.