You are probably all familiar with the human microbiome.
The collection of microorganisms like bacteria and fungi which are present
throughout our body. Without these we would not be able to function properly.
You are also familiar that there is another class of organisms called viruses.
These are often viewed as destructive, responsible for causing many diseases and having the ability
to adapt quickly to their changing environments. What you may not be aware of is that there is
equally a virome within our body. Viruses can be found in every tissue, from blood cells to our
brains and in some cases is even interwoven into the genetic code within our own cells.
Again here these viruses play key critical roles in the functioning of the entire system
we call a human. Let's explore the strange world of the viruses within your body.
If we look at the human body we know that there are roughly the same number of bacteria in our
body as we have cells. Just to give you an idea that equates to about 37 trillion bacteria.
It may come as a bit of a surprise that your body has over 10 times that amount of viruses.
These viruses are not there lying dormant waiting to cause some sort of illness.
Instead they are involved in essential body processes, forming part of our
inner ecosystem. Without them we really wouldn’t be able to survive for very long!
Our understanding of viruses is very limited and we really do not know what
most of these viruses do exactly, or even what most of them are! Currently
it is estimated that only about 1% of the viral diversity has been explored.
This means most viruses remain undiscovered, for which some scientists have the rather catchy name
viral dark matter! Despite this lack of understanding they occur throughout all
parts of our body. In a study conducted by Dr. Kei Sato from the University of Tokyo
they discovered viruses in human tissue including the brain, blood, kidney and liver.
Most of the viruses that have been discovered are considered harmful or pathogenic.
This creates a bias in the search for these missing viruses. Most literature presents viruses
as small machines that after making contact with a human cell’s surface injects its DNA or RNA code,
hijacking the cell’s machinery, turning it into a factory to make more copies of itself.
Most images of viruses portray an alien like machine
with a whole series of spikes on the surface intent only on destruction.
Yet most viruses are nor as alien as they are being portrayed.
Viruses can be transmitted by a wide range of mechanisms. Some are able to
pass viral DNA directly between human cells by integrating them into the chromosomes.
A staggering 8% of our human genome is composed of these endogenous retroviruses.
If we take an example of the DNA code for the direct production
of protein molecules then only 2% of the DNA code is required. The rest was thought to
be junk DNA. Now lots of this DNA is thought to be derived from previous virus insertions
and we have discovered that it is highly important for regulating the transcription of other genes.
Some virus genes do occur in human DNA regions that produce essential proteins. How these came
to cohabit with our DNA is unclear but they now form part of the process required for
essential functioning, so whether we should call then human or viral genes is unclear.
They form important parts of many of the human systems. One gene that is used in
the development of the human placenta comes from an endogenous retrovirus. This virus is thought
to have developed to make proteins fuse host cells together. Through the evolutionary past,
this process of gene harvesting from across the tree of life seems to have occurred many times.
The more we learn about the human body the more we realise that it truly is an ecosystem that
needs to be maintained. Like in any ecosystem an imbalance of one species can lead to the
collapse of part or the whole ecosystem. The same seems to occur in our bodies' ecosystems.
Bacteriophages are viruses that attack bacteria in our bodies.
These play a crucial role in maintaining a healthy balance in our diverse human ecosystem.
Another role that is important is the protection of outside threats
and here too viruses seem to play a crucial role. In humans hepatitis G virus can protect
against HIV, while in mice herpesvirus is known to reduce autoimmune diseases.
It is therefore thought that viruses have an important role in maintaining ‘immune tone’
in humans. This means a healthy immune system which is ready to respond to pathogens
but that is not over or under active.
The more we learn the more we seem to find this connectedness to everything around us.
We view ourselves as individuals but the reality is that we are a giant
vessel that harbours many diverse ecosystems that function together
forming the organisms known as a human. Each part is largely unaware of the larger system.
Can the same be true of us and our connection with our immediate environment and beyond?