Even healthy people carry viruses in their bodies!

On an average, healthy individuals carry about five types of viruses in their bodies and the same viruses that make us sick can take up residence in and on the human body without provoking a sneeze, cough or other troublesome symptom, says a significant study.

"Lots of people have asked whether there is a viral counterpart (to bacterial flora) and we have not had a clear answer. But now we know there is a normal viral flora and it is rich and complex," said study co-author Gregory Storch from the Washington University School of Medicine in St Louis.

In 102 healthy young adults aged 18 to 40, researchers sampled five body habitats: nose, skin, mouth, stool and vagina.

At least one virus was detected in 92 percent of the people sampled and some individuals harboured 10 to 15 viruses.

Analyzing the samples, scientists found seven families of viruses, including strains of the herpes virus that are not sexually transmitted.

Strains of papillomavirus were found in about 75 percent of skin samples and 50 percent of samples from the nose.

Not surprisingly, the vagina was dominated by papillomaviruses with 38 percent of female subjects them.

Some of the women harboured certain high-risk strains that increase the risk of cervical cancer.

Adenovirus, the virus that cause the common cold and pneumonia, also was common at many sites in the body.

It is possible that some of the viruses the researchers uncovered were latent infections acquired years ago.

"But many viruses were found in body secretions where the presence of a virus is an indicator of an active infection. Dormant or latent viruses hide in cells, not in body fluids such as saliva or nasal secretions," added lead author Kristine M. Wylie, an instructor of paediatrics.

According to researchers, it is very important to know what viruses are present in a person without causing a problem and what viruses could be responsible for serious illnesses that need medical attention.

The study appeared online in the journal BioMed Central Biology.