Many viruses persist in our bodies for life

Many common viruses responsible for childhood illnesses establish a home for life within us, shaping our health in ways that are not yet fully understood. That’s according to a new study from the University of Helsinki, published in the journal Nucleic Acids Research, which tracked the distribution and co-existence of up to 12 different virus types in nine organs of an individual.

The researchers examined tissue samples from 31 recently deceased individuals. The organs included colon, liver, lung, heart, brain, kidney, skin, blood and hair, and were analysed using next-generation sequencing and PCR. The study focused on human DNA viruses, among which 17 were identified.

“Our research demonstrates that the presence of multiple types of viruses in organs such as the kidneys, liver, heart and brain is more of a rule than an exception,” said Dr Lari Pyöriä, the lead author of the study.

In contrast to the bacterial microbiota that colonise the human body, primarily in mucosal and skin environments, the viruses were found to persist within our cells. “We found viral fingerprints even in body sites considered to be sterile,” Pyöriä said.

“They are like visitors who come for a day or two, yet end up settling for life within us,” added principal investigator Dr Maria Perdomo. “To avoid being eliminated, viruses must tweak their host cells and the immune system, and we must investigate what the long-term consequences of this interaction on our health are.”

The researchers believe that these persistent viruses can influence, directly or indirectly, the development of chronic diseases such as cancer or autoimmune diseases. However, establishing a link is far from straightforward. According to Perdomo, many common virus species have evolved alongside humans for millions of years, and there are many mechanisms, beneficial or detrimental, by which viruses can contribute to our health.

“Viruses are probably very valuable to us too; for example, in training and regulating the immune system,” Perdomo said. “Our observations encourage further research on the interplay between the virome, other microbes and the human body. The dynamic balance between these actors can have a profound impact on our wellbeing.”

Image caption: Viral nucleic acids can be seen as red dots in liver cells. Image credit: Virus infections and immunity research group, University of Helsinki.