You’ve probably heard of the human microbiome, the collection of microorganisms like bacteria and fungi that we share our bodies with, including the skin and the gut microbiome. But how much do you know about the “virome”? It is the sum of all the viruses within our body, found in every tissue from our blood to our brain, and even woven into the genetic code within our cells.
Viruses are the most enumerated organisms on Earth. While it is believed that we have about the same number of bacterial cells as human cells in our body (around 37 trillion), we probably have at least 10 times as many virus particles.
Many of these viruses are involved in essential bodily processes, forming part of our internal ecosystem. Perhaps we can say that we could not survive for long if all of them disappeared. However, we still have a long way to go before we can understand exactly what most of these viruses do, or indeed what most of them are. It has been estimated that the field of virology has so far only explored about 1% of the existing viral diversity. Most viruses remain undiscovered, they are what some scientists call “viral dark matter.”
Despite this, they are present in all parts of our bodies. A study led by Dr. Kei Sato of the University of Tokyo published in June 2020 found viruses in human tissues, including the brain, blood, kidneys, and liver. Sato’s team wanted to quantify these viruses to create a viral atlas of human tissue.
They did this by comparing the RNA sequence data with that of existing libraries of viral genomes, but this meant that they could only count the few well-known viruses already in those libraries. According to Sato, this means that there is currently a bias in the search for known viruses that are mostly harmful, known as “pathogens.”And he explains: “In addition to the biases in our genetic reference libraries, it is difficult to collect samples in healthy tissues beyond the intestine, which means that we may be overlooking many harmless or even potentially beneficial viruses.
It’s easy to think of viruses as malicious foreign intruders. After coming into contact with the surface of a human cell, a virus injects its DNA or RNA code, hijacking the cell’s machinery and effectively turning it into a factory for producing new viruses. If you imagine a virus now, think of its protein coat as similar to a spaceship, called a capsid that it uses to transport itself between cells. You may have seen the coronavirus responsible for the COVID-19 pandemic, SARS-CoV-2, with its “crown” of spikes covering the surface of the capsid.
However, Viruses Are Not As Strange As They Might Seem.
The term virus actually describes entities with very diverse attributes. As Professor Frederic Bushman, a world expert on the human microbiome at the University of Pennsylvania puts it “Sometimes our words for things in the world do not actually match what they exist. For example, viruses can be transmitted through a wide range of mechanisms. For some, the so-called endogenous retroviruses, viral DNA passes directly between human cells because they are integrated into chromosomes.
In Fact, 8% Of Our Human Genome Is Made Up Of These Endogenous Retroviruses.
Only a small fraction less than 2%, of our DNA codes for the direct production of protein molecules in a process known as and biologists used to think that the rest was not functional, some even called it to junk DNA. It is now believed that much of this DNA is derived from earlier virus insertions and we have found that it is very important in regulating the transcription of other genes. Some virus genes are found in regions of human DNA that make essential proteins. Throughout evolutionary history, these genes have been incorporated for the essential function of our bodies, so it is unclear whether we should call them human or viral genes.
A gene used in the development of the human placenta has been borrowed from an endogenous retrovirus where it first evolved to produce proteins that fuse host cells. Throughout our evolutionary past, this process of collecting genes through the tree of life seems to have occurred many times. It has been suggested that about 145 of our 20,000 genes have arisen from such horizontal gene transfer. By transferring genetic molecules between different species in this way, viruses effectively link the evolutionary tree into a complicated web.
However, viruses often get a bad rap, because the ones that get a lot of publicity have damaging effects that cause diseases like AIDS, Ebola, chickenpox, and of course COVID-19. In fact, we have very little understanding of how most viruses affect humans. There could be more than 320,000 different viruses that infect mammals, many of which are harmless, while some could provide us with benefits.
For example, some viruses called bacteriophages attack bacteria in our body and therefore have a crucial role in regulating our microbiome. Just as an invasive wild animal species can reproduce uncontrollably when it enters a new area without predators or pathogens (think cane toads in Australia or rats on tropical islands), bacteria would also override our bodies without these regulatory mechanisms.
Viruses Also Appear To Be Important In Regulating Our Immune Systems.
In humans, the hepatitis G virus can protect against HIV, while in mice the herpes virus is known to reduce autoimmune diseases. These are disorders that are a major factor in many modern human diseases, from asthma to irritable bowel syndrome. Therefore, many researchers suspect that viruses play an important role in maintaining the ‘immune tone’ in humans a healthy immune system ready to respond to pathogens that are not overactive or insufficiently active although the identity and role of specific viruses are poorly understood.
This is not to deny the damaging effects of some viruses and the devastating impacts they can have on people’s lives. Many viruses are clearly very harmful to us, and humans have developed mechanisms to counter their attacks. Bushman’s team demonstrated in April 2020 that breastfeeding reduces the incidence of potentially pathogenic viruses that grow in human cells in the baby’s gut. As a whole, the human virome is neither “good” nor “bad”, it is simply an old part of us.
Viruses And Evolution
Viruses share a deep evolutionary relationship with animals and plants. Every cell in your body is part of an unbroken chain of life that has spanned more than 3.8 billion years. Viruses have been an important part of that evolutionary dance from the beginning. The more we learn about the virome, the more we realize how some aspects are essential for a healthy life. Therefore, a revolution is expected in the way we conceive of viruses. Remember that we used to view all bacteria as dangerous ‘germs’, until we finally gained a more nuanced understanding of how they support our health disruption of the bacterial microbiome is now implicated in a wide range of diseases, including Crohn’s disease, syndrome irritable bowel, type 2 diabetes, and even mental health disorders like depression.
We are walking ecosystems: chimeras of animal cells, viruses, bacteria, fungi, and others, and maintaining the balance of these ecosystems is vital for our well-being. We have yet to understand exactly how our human virome works, but disruptions can have unforeseen consequences. Social distancing and the widespread use of virucidal chemicals, both for application in public places and for hand disinfection to reduce viral transmission, has been a crucial element in the fight against the current COVID-19 pandemic.
These lifestyle changes and others, like the way our diets change and the way we interact with other people, will likely transform our virome . As Sato concludes. In the current covid-19 pandemic, many people view viruses simply as ‘the enemy,’ but we need to better understand the potential health-promoting aspects of our human virome.”The pace of discoveries in virology is dazzling, so get ready for many more exciting discoveries that will uncover the secret ecology of our inner world.