Did you know that your body is teeming with trillions of bizarre viruses? These viruses aren’t your enemies—instead, they’re crucial for your health, protecting you from disease, and possibly even helping to fight cancer. This is a new frontier in science, something we’re only beginning to understand. Let’s explore the wild world of the human virome.
You Are a Living Ecosystem
You are, in fact, a living, breathing ecosystem made up of around 40 trillion cells. This metropolis of flesh and bone is also home to the human microbiome—another 40 trillion bacteria that have an arrangement with your body. In exchange for living here, these bacteria help you out: breaking down your meals, synthesizing vitamins in your gut, neutralizing acid in your mouth, balancing your immune system, and taking up space to prevent harmful bacteria from moving in.
This delicate balance is constantly maintained. Bacteria are selfish creatures, multiplying and testing their limits. To keep their numbers in check, your body relies on a group of deadly predators: viruses. Yes, you have at least 10 trillion viruses throughout your body. They’re literally everywhere—trillions are in your gut where most of your resident bacteria live, another 18 billion on your skin, 100 million in each drop of your saliva, and millions more in your urinary tract and cerebrospinal fluid.
While it sounds alarming, most of these viruses—particularly in the gut—aren’t harmful to you. Around 97% are bacteriophages, or phages, which are specialized viruses that hunt down bacteria but can’t infect your own cells. Instead, they kill trillions of bacteria daily, forming a unique viral ecosystem called the “virome,” which plays a critical role in keeping you healthy.
The Silent Killers Inside You
Deep within your gut, a bacteriophage called the lambda phage floats through the crowded bacterial metropolis. It has six spider-like legs, a long thin body, and a big geometric head filled with DNA. Each phage is highly specialized, only hunting a specific species of bacteria. Lambda is searching for E. coli, a versatile bacterium that’s typically beneficial to your health, synthesizing vitamins and keeping things balanced. However, certain strains of E. coli can turn harmful, invading your tissues and causing disease.
One of the virome’s main tasks is to control bacteria populations by killing off excess. Once lambda finds its target, it uses its legs to grab the bacterium and injects its genetic material inside. This genetic takeover turns the bacterium into a virus factory, churning out new phages until it bursts open, releasing a swarm of fresh lambda viruses. However, the goal isn’t to wipe out bacteria entirely—phages need a thriving bacterial community to survive. Sometimes they even integrate their DNA into the bacterial genome, lying dormant until the time is right to reawaken and kill their host.
How Viruses Can Benefit You
Surprisingly, your virome needs you to be healthy in order to thrive. It’s in their best interest. Some viruses inject genes into bacteria that actually make them beneficial to your body. For example, some help bacteria support the gut’s mucus layer, break down complex carbohydrates more effectively, or produce substances that reduce inflammation. They can even tweak the signals bacteria send to your immune system, effectively telling it, “Everything’s under control, you can relax.” This helps prevent allergic reactions and might even protect against autoimmune diseases.
The Dark Side of Viruses: Turning Bacteria Into Killers
But not all viruses are friendly. Some can turn harmless bacteria into lethal threats. Certain phages carry toxic genes that, when inserted into bacteria, transform them into deadly pathogens. Take Vibrio cholerae, the bacteria behind cholera. Most strains of Vibrio are harmless and reside in your gut without issue. However, when a bacteriophage called CTXphi infects Vibrio, it delivers genes for the cholera toxin. Suddenly, harmless bacteria become dangerous killers, releasing toxins that cause severe dehydration through vomiting and diarrhea—often leading to death if left untreated. For the phage, this is a great strategy—it ensures that both the bacteria and virus are spread to new hosts.
Similarly, Staphylococcus aureus, often found harmlessly on your skin or in your nose, can become deadly when infected by a phage known as ΦSA3ms. This phage injects genes that arm the bacteria with toxins, like superantigens, which overstimulate your immune system. The toxin floods your system, activating all your immune defenses at once, leading to chaos. Before antibiotics, infections from these mutated strains were often fatal. We have ΦSA3ms to thank for making Staphylococcus aureus even deadlier.
Viruses That Fight Cancer
Interestingly, some viruses can also help fight cancer. Known as oncolytic viruses, these viruses specialize in infecting and killing cancer cells. Examples include the Newcastle disease virus and reovirus. Unlike healthy cells, cancer cells are often defenseless against these viruses due to their compromised nature. The viruses infect cancer cells, turning them into virus factories, and ultimately killing them. Even better, this process attracts immune cells that begin attacking the tumor.
What’s remarkable is that these viruses seem to undermine the protective environment tumors create to keep immune cells at bay. Oncolytic viruses act like infiltrators in a besieged city—opening the gates and allowing your immune cells to launch a full-scale attack. Though this approach is still being studied, it shows promise, especially when used alongside chemotherapy or radiation. Oncolytic viruses may become a powerful tool in our fight against cancer, potentially saving millions of lives.
The Future of Virome Research
We’re only scratching the surface of what we know about the virome, but one thing is clear: there are trillions of potential allies inside us, working for better or worse. The next few years will surely bring more exciting discoveries about how these viruses influence our health and how we can harness them to our advantage.