All About Viruses

Podcast Transcript

Inside you right now are most probably millions of, possibly even trillions of viruses.

Some viruses are extremely deadly, but the vast majority are completely benign. They can be found in almost every type of life, including plants, animals, and bacteria.

Yet viruses are completely different from any other type of life form. In fact, it is debatable whether they are even life forms at all.

Learn more about viruses, what they are and how they work on this episode of Everything Everywhere Daily.

If you have been on Planet Earth over the last few years, you have probably become very familiar with the discussion of viruses.

Yet, in all the talk about viruses, seldom was there any attempt at explaining what a virus was or how they worked.

So, in this episode, I want to go over the basics of what viruses are, how they work, and how they were discovered.

Viruses are microscopic infectious agents that can replicate only inside the living cells of an organism.

Viruses are made up of genetic material, either double-strand DNA or single-strand RNA, enclosed in a protein coat and sometimes an additional lipid envelope.

Viruses are not made of cells and are much smaller than cells. A cell can be observed through most optical microscopes. A virus, however, can only be seen with something as powerful as an electron microscope.

The fact that viruses are not made out of cells is the reason why antibiotics are ineffective against viruses.

Viruses reproduce in a very unique way.

First, a virus attaches itself to a specific receptor on the surface of the host cell. The receptors are literally molecules that fit together on the cell and the virus.

Next, the virus or its genetic material enters the host cell.

The viral genetic material takes over the host cell’s machinery to replicate itself.

New viruses are assembled inside the host cell, using the cell’s materials as the basis for the new virus.

Finally, new viruses are released from the host cell, often destroying it, to infect other cells.

Because viruses are really just glorified strands of DNA or RNA, there is a great deal of debate as to whether viruses are, in fact, alive.

There is no clear-cut definition of what makes something alive, which is why there is debate about whether viruses are life forms. They meet some of the definitions of life, but they don’t meet many others.

For starters, all life that we can positively agree on is alive and has some sort of cellular structure. Everything from the largest animal to the smallest single-cell life form is made up of cells consisting of a cell membrane.

Viruses, as I’ve mentioned, are not made up of cells.

Another criterion for something to be alive is that it has some sort of metabolism. It will have some chemical reactions that convert energy from the environment to sustain life.

Viruses have no metabolism. They cannot generate energy, synthesize proteins, or carry out any biochemical reactions on their own. They rely entirely on the host cell’s machinery to perform these functions. Absent a host cell, they are completely and totally inert.

So, why, then, are there some people who think that viruses are alive?

For starters, they are made up of genetic material, which is the basis for all life. Unlike other lifeforms, viruses pretty much are just genetic material and nothing more.

Viruses can reproduce. They can’t reproduce independently and require material from a host cell, but they can nonetheless reproduce insofar as one virus can create many other identical viruses.

Furthermore, viruses can evolve through natural selection. In fact, given how small they are, they can sometimes evolve quite quickly. Small mutations in a virus’s molecular structure can have profound impacts and change how a virus grows or develops.

So, you can see why there is debate about whether viruses are alive. If they are alive, they are about as close to something not being alive as possible. Likewise, if they aren’t alive, then they are borderline to becoming a life form.

Another big question is how viruses arose. Did they predate cells, did they come after the creation of cells, or did they evolve with them at the same time?

The answer is that we don’t really know. Viruses don’t make fossils. However, there are multiple theories about their origin. There are three popular theories as to how viruses developed.

The first is the Regressive Hypothesis. This holds that viruses may have evolved from small cells that were parasites. Over time, they lost unnecessary genes and cell structures, becoming more dependent on host cells until they were nothing but genetic material.

The second theory is the Cellular Origin Hypothesis. This theory contends that viruses might have originated from pieces of DNA or RNA that “escaped” from the genes of a larger organism. Unlike the Regressive Hypothesis, this doesn’t assume that full cells devolved; rather, bits of genetic material just got loose and began reproducing.

The third theory is the Co-evolution Hypothesis. This hypothesis contends that viruses might have evolved alongside their host cells in the primordial soup of early Earth, representing ancient, self-replicating molecules that developed the ability to infect cells.

Personally, the Co-evolution Hypothesis seems to make the most sense to me, but my opinion is based pretty much on nothing. Absent discovering DNA-based life on other planets or artificially creating life in the laboratory, it is unlikely we will ever discover the true reason.

Given the nature of viruses, they were discovered rather late.

Humans had always lived alongside viruses and they were very familiar with the effects of viruses, even if it was nothing more than the common cold.

The story really begins in 1884. A researcher named Charles Chamberland developed a porcelain filter known as the Chamberland filter, which could remove bacteria from solutions.

The Chamberland filter was used as a water filter that could remove bacteria, the smallest known life form at the time.

In 1892, Dmitri Ivanovsky, a Russian botanist, used the Chamberland filter to study a disease affecting tobacco plants. He found that the filtered sap from diseased plants could still cause disease in healthy plants, suggesting the presence of an infectious agent smaller than bacteria.

In 1898, Martinus Beijerinck, a Dutch microbiologist, conducted similar experiments and confirmed Ivanovsky’s findings. He coined the term “virus” (from the Latin word for poison) to describe the infectious agent and concluded that it was a new type of pathogen that could replicate in living cells.

In 1901, American army physician and medical researcher Walter Reed and his colleagues demonstrated that yellow fever was caused by a filterable agent and identified it as a virus… the first human virus discovered.

In the succeeding years, more and more diseases were discovered that couldn’t have been bacteria-based. They were based on these mysterious minuscule substances known as viruses.

In 1935, American biochemist Wendell Stanley successfully crystallized the tobacco mosaic virus, demonstrating that viruses could be studied like chemical substances. This work earned him a Nobel Prize in Chemistry in 1946 and provided insights into the molecular nature of viruses.

The 1940s and 50s saw the rise of electron microscopes, which were finally able to see what viruses looked like.

Finally, in 1952, Alfred Hershey and Martha Chase used bacteriophages to demonstrate that DNA, not protein, was the material that genes were made of, and proved that viruses are made out of DNA. Work that was awarded the Nobel Prize in Medicine in 1969.

It is believed that there are currently millions of different types o viruses that exist on Earth, the vast majority of which have not been identified. Approximately 11,000 different types of virus have been identified and cataloged so far.

Given the genetic nature of viruses, almost all viruses can only infect and reproduce with certain specific species. A virus that infects a plant cannot replicate with animal cells, and vice versa.

The number of different species a virus can infect is known as its host range.

For example, smallpox was a disease transmitted via a virus, and it could only be transmitted from human to human. It was highly specialized and had a very narrow host range.

The Influenza A virus, on the other hand, has a much wider host range and can infect pigs, birds, and humans.

Categorizing viruses is much more challenging than categorizing other lifeforms, given their microscopic nature.

In 1966, the International Committee on Taxonomy of Viruses, or ICTV, was created to tackle this problem.

They created a 15-layer system that is analogous to the system used to categorize cellular life. It goes from the highest rank of realm down to the lowest rank of species.

Unlike traditional taxonomy, these broad realms are not based on common ancestors but rather on shared traits.

In conjunction with this system, there is another system called the Baltimore system, which was developed by the Nobel Prize-winning biologist David Baltimore. It is a six-category system that categorizes viruses based on their genetic makeup: if it is DNA or RNA, how many strands it has, and how it replicates.

There are other ways to categorize viruses as well, including their morphology and the diseases they cause.

As you are probably aware, viruses are the cause of many serious diseases that affect humans. The common cold is caused by viruses as are much more serious diseases such as influenza, HIV, Ebola, and of course COVID-19.

There is no one single means of spreading viral infections. Some viruses are spread through the air, some through water and other fluids, and some can be spread via physical contact such as shaking hands.

How a virus spreads is due in large part to its morphology or its shape and structure. Many people fear deadly viruses like the ebola virus “becoming airborne.” This is almost an impossibility. It would require mutating into something totally different to change its transmission vector that radically. If it changed that much, then it would no longer be the ebola virus.

Fighting viruses is very different than fighting bacteria.

The first strategy for attacking a viral infection is to simply try and stop the spread of the virus. This involves identifying the transmission vector and then interrupting it.

A second strategy is to create a vaccine, which allows the body’s immune system to fight the virus.

If you remember to my previous episode on the subject, this was the strategy behind the eradication of smallpox. Widespread vaccinations, plus identifying and isolating people infected, allowed the disease to eventually be eliminated.

The other big approach to fighting viral diseases are antiviral drugs.

Antiviral drugs tend to target very specific viruses. They do so by blocking the replication zones on the virus. They might do this by having DNA fragments in the drug that viruses will latch onto instead of latching onto cells.

Developing antiviral drugs can be very expensive and time consuming given how focused they have to be for the virus they are targeting.

There are also Virucides, which are biological or chemical agents that can outright kill viruses. The problem with virucides is that they can often damage cells. As such, virucides tend to be used outside the body and not ingested.

I should close by noting that not all viruses are bad. One of the most promising fields of medicine is gene therapy.

Gene therapy is a medical technique that involves altering or manipulating an individual’s genes to treat or prevent disease.

One of the primary methods of doing this is harnessing the power of a virus to insert DNA into a cell. Some gene therapy techniques involve modifying a virus such that it will transport a beneficial change directly into a cell.

As of today, the majority of gene therapy trials are involved in the treatment of cancer.

Viruses are an extremely large part of biology as we know it on the planet Earth. Viruses can be found in almost every ecosystem on every corner of the planet, and some can probably be harmlessly found inside you right now.

Regardless of whether you consider them to be alive or not, there is no doubt that viruses are some of the most important parts of the biological world.