The Hidden World of Viruses Inside Us
The Viruses We Know and the Ones We Don’t
When we hear the word “virus,” we often think of illnesses like the flu or the devastating consequences of smallpox. These pathogens are well-known for their ability to make us sick, sometimes with life-threatening results. However, the reality is that our bodies are teeming with viruses that don’t make us ill. In fact, scientists estimate that there are tens of trillions of viruses living inside us at any given time. Despite their abundance, only a small fraction of these viruses have been identified, and much about their role in our health remains a mystery. While many of these viruses are benign, some may even play a beneficial role in our overall well-being. However, without further research, the full extent of their impact on our health remains unclear.
Unveiling the Human Virome: A Major Scientific Initiative
To address this knowledge gap, a groundbreaking project known as the Human Virome Program has been launched. This ambitious five-year initiative, supported by $171 million in federal funding, involves five universities working together to identify and study the immense array of viruses within the human body. The program will involve collecting a wide range of samples, including saliva, stool, blood, and breast milk, from thousands of volunteers. By analyzing these samples using advanced artificial intelligence systems, researchers hope to gain a deeper understanding of how the human virome influences our health. According to Dr. Frederic Bushman, a microbiologist at the University of Pennsylvania and one of the program’s leaders, this effort is expected to uncover far more information about the human virome than has been discovered to date.
Early Discoveries and the Evolution of Viral Research
The concept of the human virome is not entirely new. Over a century ago, scientists began uncovering hints of its existence when they discovered phages—viruses that infect bacteria—in stool samples. Since then, phages have been found in various parts of the body, including the mouth, lungs, and skin. Later, researchers identified viruses that could infect human cells without causing significant symptoms. For example, cytomegaloviruses, which can colonize nearly every organ in the body, are so widespread that the majority of the global population is infected with them. The early 2000s saw a major breakthrough in viral research with the advent of new genetic sequencing technologies. These tools not only revealed more viruses in saliva, blood, and stool but also allowed scientists to estimate the sheer number of viruses present in the human body. For instance, researchers found that each gram of stool contains billions of phages, highlighting the vast and complex ecosystem of viruses within us.
The Diversity and Complexity of the Human Virome
The study of the human virome has revealed that it is far more diverse and complex than previously imagined. Each person’s gut alone may harbor hundreds or even thousands of different phage species. Moreover, the composition of viruses can vary significantly from one individual to another, even among people who share a close living environment, such as spouses. As scientists study more individuals, they continue to discover new viral species at an unprecedented rate. Dr. Evelien Adriaenssens, a phage biologist at the Quadram Institute in Norwich, England, estimates that there could be tens of millions of viral species waiting to be identified. Furthermore, the study of viruses that infect human cells has also revealed unexpected diversity. For example, in 1997, researchers in Japan discovered an entirely new family of viruses known as anelloviruses in a patient’s blood. Recent studies have identified over 800 new species of anelloviruses, bringing the total number of known species to more than 6,800.
Rethinking the Definition of a Virus
Recent discoveries about the human virome have also raised questions about what defines a virus. Traditionally, viruses are understood as consisting of a protein shell that encases either double-stranded DNA or single-stranded RNA. However, scientists are now finding that the human body also contains minuscule, free-floating rings of RNA that challenge this classic definition. Additionally, many viruses are adept at evading detection. Some viruses can hide inside host cells for years, embedding their genes into the host’s DNA before replicating. These challenges highlight the need for innovative tools to study the human virome. Dr. Pardis Sabeti, a computational biologist at the Harvard T.H. Chan School of Public Health, emphasizes that entirely new technologies will be required to uncover the full extent of the human virome. The Human Virome Program is at the forefront of this effort, utilizing artificial intelligence to identify subtle features of viral genes and better understand their role in human health.
Viruses as Partners: Rethinking Their Role in Health
The discovery of the human virome has led to a paradigm shift in how we view viruses. Far from being simple predators, viruses appear to have a complex and often cooperative relationship with their hosts. For example, phages, once seen as ruthless killers of bacteria, are now understood to form partnerships with their bacterial hosts. These relationships can benefit both parties, as phages can transfer genes between microbes, potentially enhancing bacterial survival. This partnership may also have positive implications for human health. Research has shown that phages can distribute defensive genes that help bacteria—and potentially their human hosts—resist harmful pathogens. Similarly, some viruses, such as cytomegaloviruses, may play a role in protecting against certain diseases. For instance, studies led by Dr. Shadmehr Demehri, a cancer immunologist at Harvard, suggest that cytomegaloviruses could help prevent skin cancer by targeting and destroying damaged skin cells before they develop into tumors. These findings challenge the long-held view of viruses as purely harmful entities and open up new possibilities for understanding their role in maintaining human health.
As the Human Virome Program and other research initiatives continue to uncover the secrets of the human virome, we may discover even more surprising ways in which viruses contribute to our well-being. This growing understanding of the virome has the potential to revolutionize our approach to medicine, from treating diseases to preventing cancer. By exploring this vast and intricate ecosystem within us, scientists are poised to make groundbreaking discoveries that could reshape our understanding of human health for generations to come.
