When we think of viruses, we often think of the biological agents responsible for Influenza,
Ebola, or the COVID-19 Pandemic. The damage caused by these viruses on society is significant.
But why do viruses infect us? What role do they have in biology? And is there a way
we can harness viruses to benefit humanity? Let’s start by looking at what a virus is.
Viruses are small infectious agents made up of genetic material -- either DNA or RNA --surrounded
by a protective protein layer called the capsid. The capsid is made up of identical building blocks
known as capsomers that fit together to make the 3D structure of the virus. These can be
classified into non-enveloped viruses, that can have a complex, helical, or icosahedral figure,
and enveloped viruses, which are spherical, as the capsid is surrounded by a membrane.
Unlike most other biological agents, viruses can't reproduce on their own. Instead,
they infect a host cell, hijack the cell's machinery, and force it to produce new viruses.
The type of virus determines how it gets inside a cell. Some non-enveloped viruses
have proteins on their surface that bind to receptors on the outside of cells.
Think of the viral surface protein as a key that fits into a lock on the cell’s surface.
If the protein fits, the cell is unlocked and the virus can enter.
Other non-enveloped viruses attach to the outside of the cell and essentially
poke a needle through the membrane to deposit viral genetic material inside.
Enveloped viruses, on the other hand, are surrounded by a membrane like the one on cells.
This allows the virus to fuse with the cell, releasing the capsid inside.
Regardless of the strategy viruses use to enter the cell,
the process that follows is the same. The viral genetic material ends up at the ribosomes,
the cellular machinery that will “translate” the viral genetic material into proteins.
These come together to form new viruses, which can leave the cell, either by pushing
through the membrane or by lysing it, which can eventually lead to cell death.
The human body has natural defenses against viruses, such as immune cells that attack
them and antibodies that bind to them. After a virus is successfully eliminated, the immune
system retains a memory of the pathogen. This way, the next time the same virus infects us,
our bodies can respond faster and more efficiently. Unfortunately, our bodies
are not always capable of eliminating the virus. In this case, the best way to protect ourselves
is through vaccines, a form of artificial immunity that involves administering low doses of weakened
viruses to the body. This mimics the process of natural immunity, allowing the body to generate
a memory of the virus without the vaccinated individual actually developing the disease.
When no vaccine or treatment exists and the body cannot mount a sufficient attack on its own,
we are at risk of the virus replicating out of control and spreading throughout the population.
A prime example of this is the COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2. This
virus is thought to be zoogenic—meaning it was first transmitted from animals to humans.
The first outbreak was recorded in Wuhan, China in December of 2019,
and the virus quickly spread across the globe, infecting over 20 million people,
and killing at least 736,766, as of August 2020. Despite all the harm that viruses can cause,
most of them don’t actually infect humans. In fact, some are critical to our survival.
Bacteriophages, for instance, are complex viruses that help us fight off harmful bacteria. They
hijack the bacteria that are infecting the body and force them to halt the production
of harmful bacterial components, stopping the damage that the bacteria were causing.
Since bacteriophages do not damage our cells in the process, they have been used to fight
bacterial infections like E.coli and staph. As bacteria become more resistant to antibiotics,
antibiotics can fail in protecting us, which is where bacteriophages can become especially useful.
With new technology, we are learning how to harness viruses to use them for our benefit.
Nowadays we treat some as messenger vessels, by removing the potentially dangerous genes
viruses would normally insert to our DNA and replacing them with sequences
that can be useful for us. For example, the herpes virus has been used to treat cancer, by
replacing the genetic material of the virus with new DNA that can target and attack tumor cells.
Although there is still a lot to be learned about viruses,
it is becoming clear that they can be more than just the diseases they are known to cause.
They might even become the next superheroes of medicine.