Study Reveals Insights on Viruses in Healthy Individuals

Even those of us who consider ourselves healthy are likely harboring viruses within our bodies. These agents can, at times, trigger diseases, but they often remain inactive, sneaking under the radar to avoid elimination.

A recent study has enhanced our understanding of common viruses that reside within healthy people’s cells and how much viral material they usually contain. Researchers from Harvard Medical School analyzed data from over 917,000 individuals, focusing on blood and saliva samples to assess viral DNA levels in instances where these infections did not escalate into disease.

By evaluating genetic fragments for what’s termed as viral load, the researchers could identify which viruses were present and gauge the immune system’s effectiveness in combating them.

The study linked viral load levels to specific regions in human DNA, exploring the correlation between certain genetic traits, demographics like age and sex, and the ability to manage viral presence. “We’re reaching a point where human genetics can help us answer fundamental questions about pathology resulting from viruses,” says Nolan Kamitaki, a geneticist and the study’s lead author.

Data pointed to 82 specific locations in the human genome associated with viral DNA, particularly in the Major Histocompatibility Complex (MHC), which plays a critical role in the immune response.

Different patterns began to emerge for various viruses. For instance, the Epstein-Barr virus (EBV) increased in prevalence with age, while the herpes virus HHV-7 showed a decline after middle age. Interestingly, EBV levels tended to peak in winter and dip during summer, which wasn’t the case for all viruses.

Utilizing a statistical method called Mendelian randomization, the team outlined connections between particular viruses and various diseases.

They discovered a high viral load of EBV significantly raised the risk of developing Hodgkin’s lymphoma later on, whereas no direct connection was established between EBV and multiple sclerosis (MS), despite EBV being recognized as a trigger for MS. This suggests that the immune system’s response to EBV, rather than the quantity of the virus itself, plays a critical role.

“This finding illustrates the significance of virus research in extensive genetic databases,” Kamitaki emphasizes.

As for the relationship between EBV and Hodgkin’s lymphoma, the findings imply that antiviral treatments might lower the risk of developing this type of lymphoma, though this still requires further study.

Other factors, beyond genetics, also influenced viral DNA load, including age, sex, and whether an individual smoked. It appeared that most viruses were found more frequently in men than women.

These insights can help researchers delve deeper into why one person may face a higher disease risk than another, even with similar viral backgrounds. It turns out that these viruses are quite common; for instance, three types known as anelloviruses are present in 80-90% of the population, yet their exact relationship with diseases remains unclear.

It’s important to note that the study primarily focused on DNA viruses, which integrate with and manipulate human DNA. Future research could also encompass RNA viruses like coronaviruses, which behave differently.

Moreover, the influence of old viruses embedded in our genomes—ones that can no longer replicate—might have unexpected effects on health.

“It’s fascinating to see how much information DNA can offer about biological processes and how our genes, habits, and biology interact with those processes,” adds geneticist Steven McCarroll.

The findings have been published in Nature.