While we have extensively studied the role of bacteria that call our bodies' home, we have yet to achieve that level of understanding with viruses. In fact, the study of the populations of viruses that exist in the human body, the virome, is in its infancy.
We generally consider viruses an enemy that can cause diseases from the common cold to Ebola. New viruses are discovered regularly and scientists are beginning to appreciate the diversity of viruses and their roles in nature. Some don't infect people at all, while others are actually beneficial members of the human microbiome. The microbiome is the collection of microbes that colonize our bodies.
Viruses have coevolved with the organisms they infect for millennia. In fact, about 8 percent of the human genome is derived from sequences that resemble infectious retroviruses, which are similar to HIV. These human endogenous retroviruses, or HERVs, are remnants of ancestral retroviral infections that became part of the human genome. HERVs are thought to have played an important role in the evolution of humans. The sequences of the HERVs have revealed that most of them have acquired so many mutations that they can no longer produce viral proteins. There are three known that produce viral particles. One of them HERV-W, has proteins on its surface that are required for the formation of the placenta. Without this protein, pregnancy associated high blood pressure, pre-eclampsia, can occur.
Another virus can actually limit the spread of HIV. Most people infected with the GB virus GBV-C, also known as hepatitis G, don't have any symptoms of liver infection. However, people with GBV-C and HIV have a slower progression to AIDS. GBV-C appears to prevent HIV from infecting cells. GBV-C also reduces HIV virus levels in the blood and improves the immune response, which contributes to improved outcomes of HIV infections.
Mammalian viruses also offer protection from bacterial pathogens. A certain family of herpesvirus increases resistance to infections by Listeria, the third leading cause of death among foodborne pathogens, and Yersinia pestis, which causes the plague. Another type of virus called bacteriophage infect bacteria. We have some of these kinds of viruses in our guts that destroy pathogenic bacteria and keep our microbiome healthy. Over half the world's population hosts the common bacteriophage crAssphage. CrAssphage infects a common type of gut bacteria called Bacteriodetes, which are thought to play a major role between gut bacteria and obesity.
Viruses are the most abundant organisms on earth, and each person has their own unique population of them, their virome. Efforts are underway to determine the role of the virome in both making us sick and keeping us healthy.
Medical Discovery News is hosted by professors Norbert Herzog at Quinnipiac University, and David Niesel of the University of Texas Medical Branch. Learn more at www.medicaldiscoverynews.com.