Leisha I am not even sure we know what a virus is. No one has ever seen one.
Despite their profound impact on life and their ubiquity in the natural world, we don’t really know what viruses are. This fundamental question continues to puzzle scientists, challenging our very definition of life. Viruses exist in a perplexing gray area between living and non-living entities, defying easy classification. Their origins remain a mystery – did they evolve from more complex organisms, or did they precede cellular life altogether? We’ve only scratched the surface in terms of discovering the true diversity of viruses, with estimates suggesting we’ve identified just a tiny fraction of those that exist. Their roles in ecosystems and within our own bodies likely extend far beyond the pathogenic functions we typically associate with them, but these remain largely unexplored.
Viruses have played a significant, yet not fully understood, part in evolution by transferring genetic material between species. The discovery of giant viruses and viruses that infect other viruses continues to expand and complicate our understanding.
Interestingly, while we use sophisticated DNA and RNA testing methods to identify and study viruses, we’ve never actually “seen” a virus in the conventional sense. What we often refer to as images of viruses are typically artistic renderings or images from electron microscopes, which don’t provide a direct visual representation in the way we see other microscopic organisms. This inability to directly observe viruses adds another layer of complexity to our understanding and classification of these entities. This persistent uncertainty about the fundamental nature of viruses underscores the need for continued research, as we may need to revise our basic concepts of life, evolution, and the role of viruses in the biosphere as we learn more.
It’s true, most viruses have a pathogenic relationship with their hosts – meaning they cause diseases ranging from a mild cold to serious conditions like severe acute respiratory syndrome (SARS). They work by invading the host cell, taking over its cellular machinery and releasing new viral particles that go on to infect more cells and cause illness.
But they’re not all bad. Some viruses can actually kill bacteria, while others can fight against more dangerous viruses. So like protective bacteria (probiotics), we have several protective viruses in our body.
Protective ‘phages’
Bacteriophages (or “phages”) are viruses that infect and destroy specific bacteria. They’re found in the mucus membrane lining in the digestive, respiratory and reproductive tracts.
Mucus is a thick, jelly-like material that provides a physical barrier against invading bacteria and protects the underlying cells from being infected. Recent research suggests the phages present in the mucus are part of our natural immune system, protecting the human body from invading bacteria.
Phages have actually been used to treat dysentery, sepsis caused by Staphylococcus aureus, salmonella infections and skin infections for nearly a century. Early sources of phages for therapy included local water bodies, dirt, air, sewage and even body fluids from infected patients. The viruses were isolated from these sources, purified, and then used for treatment.
Phages have attracted renewed interest as we continue to see the rise of drug resistant infections. Recently, a teenager in the United Kingdom was reportedly close to death when phages were successfully used to treat a serious infection that had been resistant to antibiotics.
Nowadays, phages are genetically engineered. Individual strains of phages are tested against target bacteria, and the most effective strains are purified into a potent concentration.
These are stored as either bacteriophage stocks (cocktails), which contain one or more strains of phages and can target a broad range of bacteria, or as Adapted bacteriophages, which target specific bacteria.
Before treatment, a swab is collected from the infected area of the patient, cultured in the lab to identify the bacterial strain, and tested against the therapeutic phage stocks.
Treatment can be safely administered orally, applied directly onto wounds or bacterial lesions, or even spread onto infected surfaces. Clinical trials for intravenous administration of phages are ongoing.
Beneficial viral infections
Viral infections at a young age are important to ensure the proper development of our immune systems. In addition, the immune system is continuously stimulated by systemic viruses at low levels sufficient to develop resistance to other infections.
Some viruses we come across protect humans against infection by other pathogenic viruses.
For example, latent (non-symptomatic) herpes viruses can help human natural killer cells (a specific type of white blood cell) identify cancer cells and cells infected by other pathogenic viruses. They arm the natural killer cells with antigens (a foreign substance that can cause an immune response in the body) that will enable them to identify tumour cells.
This is both a survival tactic by the viruses to last longer within their host, and to get rid of competitive viruses to prevent them from damaging the host. In the future, modified versions of viruses like these could potentially be used to target cancer cells.
Pegivirus C or GBV-C is a virus that does not cause clinical symptoms. Multiple studies have shown HIV patients infected with GBV-C live longer in comparison to patients without it.
The virus slows disease progression by blocking the host receptors required for viral entry into the cell, and promotes the release of virus-detecting interferons and cytokines (proteins produced by white blood cells that activate inflammation and removal of infected cells or pathogens).
In another example, noroviruses were shown to protect the gut of mice when they were given antibiotics. The protective gut bacteria that were killed by the antibiotics made the mice susceptible to gut infections. But in the absence of good bacteria, these noroviruses were able to protect their hosts.
The future of therapeutic viruses
Modern technology has enabled us to understand more about the complexities of the microbial communities that are part of the human body. In addition to good bacteria, we now know there are beneficial viruses present in the gut, skin and even blood.
Our understanding of this viral component is largely in its infancy. But it has huge potential in helping us understand viral infections, and importantly, how to fight the bad ones. It could also shed light on the evolution of the human genome, genetic diseases, and the development of gene therapies.
We don’t really know what viruses are, and this fundamental question continues to puzzle scientists. Viruses exist in a gray area between living and non-living entities, challenging our very definition of life. Here are some key points that underscore our limited understanding:
- Origin mystery: We’re still unsure about how viruses originated. Did they evolve from more complex organisms? Or did they precede cellular life?
- Classification dilemma: Viruses don’t fit neatly into the tree of life. They’re not considered truly alive by many definitions, yet they possess genetic material and can evolve.
- Functional ambiguity: While we often focus on their pathogenic roles, viruses likely serve numerous unknown functions in ecosystems and within our own bodies.
- Vast unknown: It’s estimated that we’ve only discovered a tiny fraction of existing viruses. The true diversity and roles of viruses in nature remain largely unexplored.
- Evolutionary role: Viruses have played a significant part in evolution, transferring genetic material between species, but the full extent of their influence is still being uncovered.
- Beneficial aspects: We’re only beginning to understand how some viruses might be beneficial or even essential to their hosts.
- Size and structure variations: The discovery of giant viruses and viruses that infect other viruses continues to expand our understanding of what constitutes a virus.
This uncertainty about the fundamental nature of viruses underscores the need for continued research. As we learn more, we may need to revise our basic concepts of life, evolution, and the role of viruses in the biosphere.
