Washington: 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 symptoms, according to a new study.
In fact, healthy individuals carry about five types of viruses on their bodies, on average, researchers have found. While everyone is familiar with the idea that a normal bacterial flora exists in the body, scientists have wondered whether there is a viral counterpart. In 102 healthy young adults ages 18 to 40, the researchers in the new study sampled up to five body habitats,nose, skin, mouth, stool and vagina. The study's subjects were nearly evenly split by gender.
At least one virus was detected in 92 per cent of the people sampled, and some individuals harboured 10 to 15 viruses. "We were impressed by the number of viruses we found," said lead author Kristine M Wylie, an instructor of pediatrics at Washington University School of Medicine in St Louis. "We only sampled up to five body sites in each person and would expect to see many more viruses if we had sampled the entire body," Wylie said.
Scientists led by George Weinstock, at Washington University's Genome Institute, sequenced the DNA of the viruses recovered from the body, finding that each individual had a distinct viral fingerprint. About half of people were sampled at two or three points in time, and the researchers noted that some of the viruses established stable, low-level infections.
The researchers don't know yet whether the viruses have a positive or negative effect on overall health but speculate that in some cases, they may keep the immune system primed to respond to dangerous pathogens while in others, lingering viruses increase the risk of disease. Study volunteers were screened carefully to confirm they were healthy and did not have symptoms of acute infection.
Analysing the samples, the scientists found seven families of viruses, including strains of herpes viruses that are not sexually transmitted. For example, herpesvirus 6 or herpesvirus 7 was found in 98 per cent of individuals sampled from the mouth.
Certain strains of papillomaviruses were found in about 75 per cent of skin samples and 50 per cent of samples from the nose. Novel strains of the virus were found in both sites. Not surprisingly, the vagina was dominated by papillomaviruses, with 38 per cent of female subjects carrying such strains.
Some of the women harboured certain high-risk strains that increase the risk of cervical cancer. These strains were more common in women with communities of vaginal bacteria that had lower levels of Lactobacillus and an increase in bacteria such as Gardnerella, which is associated with bacterial vaginosis.
Adenoviruses, the viruses that cause the common cold and pneumonia, also were common at many sites in the body.