History of viruses and bacteria 25th November 2021 – Tags: , , ,

What is a virus?

According to Peter Crosta (UoI), “viruses are microscopic organisms that exist almost everywhere on the planet. They can infect animals, plants, fungi and even bacteria….. Viruses vary in complexity. They consist of genetic material, RNA or DNA, surrounded by a protein, lipid (fat) or glycoprotein envelope”.

Talking about viruses can be complicated because each one is different. Some viruses can kill you outright, others make you more vulnerable to other diseases, while others can cause other adverse reactions.

Another complication when talking about viruses is that they affect various organisms differently. For example, influenza C has a near-fatal effect on birds, but in humans it causes a mild cold.

Viruses are the most abundant organisms on the planet. They infect host cells, but do not replace them. Viruses cannot be cured, but vaccination and immunisation can stop their spread.

How are viruses transmitted?

The genetic purpose of viruses is to reproduce. They are relentless and incredibly efficient at this task. The most “successful” viruses have a high transmission rate. For example, Covid-19 is thought to have spread so quickly because it had an R-rate of 1.4. This means that each person who became infected had the potential to infect at least 4 other people. Whereas influenza has an R-rating of 1.1.

Each virus spreads slightly differently, here are some examples of how they can spread:

  • By physical contact (Touch…)
  • Exchange of body fluids (saliva, blood, sweat, semen)
  • Airborne pathogens (from sneezing and coughing)
  • Food contamination
  • Insect bites
  • Contaminated water

Some viruses can live outside an organism for many days. This means that they can transfer to an object and survive there until another organism touches it again. These types of viruses are particularly dangerous, but can be eliminated by regular cleaning of surfaces.

The incubation period is what scientists call the time when the virus begins to reproduce in the host’s body. Some viruses show symptoms at this time, while others – such as rabies – do not show any symptoms until it is too late.

How long is someone contagious?

The most successful viruses are contagious for a long time. The length of time one is contagious after contracting a viral infection varies depending on the virus.

For example, chickenpox patients are still contagious 5 days after the appearance of the spots. CoronaVirus (SARS-CoV-2) patients are thought to be contagious up to 14 days after the onset of the first symptoms. Measles is contagious for about 10 days after the appearance of the first symptoms.

The real danger of the viruses is that they are contagious before the first symptoms appear. That is when they spread the most.

Can the virus evolve?

The more a virus spreads, the more likely it is to evolve.

When viruses make copies of themselves, they do not always make exact copies. These erroneous copies are called mutations. AIDS does this frequently, making more than a billion copies of itself a day.

Some mutations have a higher survival rate than others or even than the original virus. If this mutation survives, it starts making its own copies. This is natural selection at its most basic.

¿Existen virus amistosos?

Not all viruses are bad. In fact, our digestive system is full of friendly viruses. This type of partnership is called a symbiotic relationship. Viruses have discovered that they find it easier to survive by collaborating with the host.

We don’t just have viruses that help us digest food. We also have some viruses that work alongside our immune system to fight off any aggressive bacteria that enter our body.

Types of viruses

There are millions of viruses that have been discovered, and many more that we have yet to discover. We will discuss some of the world’s most dangerous viruses later in the article, but for now, let’s look at some of the most common types of viruses.

Arguably one of the most common viruses is the flu. Everyone reading this article has probably had it at least once. Influenza is a virus that spreads and evolves rapidly, with new strains appearing every year.

Other common viruses include mumps, measles, chickenpox and rubella.

What viral diseases can viruses cause?

Viral diseases are any condition that develops as a result of contracting a virus. Here are some of the most common viral illnesses:

  • Smallpox
  • The common cold and the different types of flu
  • Measles, mumps, rubella, chickenpox and shingles
  • Hepatitis
  • Herpes and cold sores
  • Poliomyelitis
  • Rabia
  • Ebola and Hanta fever
  • HIV, the virus that causes AIDS
  • (SARS)

¿Qué es una bacteria?

bacteria vs virus

Bacteria are single-celled organisms. Their cell structure is much simpler than that of the average cell in the human body. In particular, they have no nucleus (the “brain” of the cell). Instead, they contain a single loop of DNA.

There are 5 main categories of bacteria, based on their shape:

  • Spherical
  • Rod (bacilos)
  • Spiral (spirilla)
  • Coma (vibrios)
  • Corkscrew (espiroquetas)

For every cell in the human body, we have about 10 bacteria. Most of them are found in our digestive system. They are an essential part of it.

Not all bacteria are bad, in fact there are many good types. And exposing yourself to a small amount of new bacteria is a good way to build up immunity.

What is the difference between a virus and a bacterium?

Bacteria are living cells, they are an organism in their own right. They do not depend on anything else to live. Viruses, on the other hand, are not technically alive, as they cannot exist with the help of a host.

Why distinguish between bacteria and viruses?

Because they are so different that they need different treatment when they start to cause problems. Doctors want to make sure they only prescribe antibiotics when they need to, because if they get it wrong they can develop more antibiotic-resistant super strains.

How do bacteria reproduce?

In the world of bacteria, there is no falling in love, no long walks on the beach, no getting down to business… Instead, bacteria reproduce by binary fission.

Binary fission is the process by which a single-celled organism divides into two. These two cells are exactly the same.

It may seem like a slow process, but take a look at this case of E coli.

If conditions are right (heat and humidity), in 7 hours one cell can turn into 2,097,152 bacteria. Give them another hour and there are 16,777,216 of them. Scary stuff.

El mecanismo de supervivencia de las bacterias

In addition to being able to reproduce at an impressive rate, bacteria need other tactics to survive. Some bacteria form an endospore.

This is an outer covering that protects the bacteria from hostile environments. They can protect bacteria from threats such as excessive heat, UV rays and even disinfectants.

Viruses and evolution

One of the most dangerous things about viruses is that they are incredibly efficient at evolving. So much so that science and treatments cannot always keep up with them. Let’s take a look at what this process looks like and the difficulties scientists face when trying to study viruses.

Where does the virus come from?

There is no simple answer to this question. In fact, in the field of virology (the study of viruses) there are three main theories about the origin of viruses. And there is no universally accepted theory.

The three theories are:

  • The progressive theory
  • The regressive theory
  • The theory of the first virus

Read on to learn more about each of these theories.

Progressive hypothesis

These theories have developed because of the similarity between the retrovirus family and the retrotransposons in the human body (often referred to as eukaryotic genomes). These genomes make up about 42% of the genomes in our bodies.

Both use coding RNA to replicate each time they enter a new cell. They also use a similar method to enter and exit cells. Viruses are thought to have learned or evolved from these retrotransposons.

Regressive hypothesis

This hypothesis infers that viruses arose through a reductive process. This theory states that the genomes of eucariotas and Rickettsia prowazekii have enough DNA in common to show that they have a common ancestor.

This theory therefore suggests that viruses have complex ancestors that were once living things, possibly even bacteria. Through a process of reductive evolution they have evolved into the cell-invasive systems they are now.

The first virus hypothesis

This theory differs from the other two, as it does not assume that cells existed before viruses, hence the name “first virus hypothesis”.

Since 2005, it has been suggested that viruses were the first reproductive entity and existed in the pre-cellular world. This would make them the oldest known form of “life”.

The theory suggests that cells, as we know them, arose from mutated viruses. They developed nuclei and became more complex than their predecessors.

How did viruses evolve?

There is no agreement on the origin of viruses. And the answer may be more complex than a single correct theory.

There is such a wide and varied variety of viruses in the world that some scientists have suggested that viruses may have evolved separately in multiple ways. This theory is reflected in wider evolution, where we see creatures evolving with the same traits at opposite ends of the world.

It is possible that there are some viruses that developed through progressive methods, while there are others that arose through regressive processes. The “virus-first” theory continues to hold weight.

Bacteria evolution

The next step in understanding the history of viruses and bacteria is to look at the evolution of bacteria.

As mentioned above, bacteria (like viruses) evolve rapidly. This is one of the key elements of their survival.

Bacteria classification

Bacteria are classified according to their shape. They can exist as single cells, chains or even clusters. There are 5 main categories:

  • Sferic(cocos)
  • Rod (bacilos)
  • Spiral (spirilla)
  • Coma (vibrios)
  • Corkscrew (espiroquetas)

Bacteria are found almost everywhere in the world. They live in the air, in the soil, in Antarctica and even inside us.

What factors affect the growth of bacteria?

The more you know about the factors that affect bacterial growth, the more you can prevent the spread of unwanted bacteria.

There are six key factors that affect bacterial growth:

  • Available water
  • pH
  • Temperature
  • Nutritional concentration
  • Availability of salts and ions
  • Gaseous concentration

Bacteria thrive in warm, moist environments, such as food left at room temperature for a long time. They also avoid direct sunlight, as UVB rays can kill them. They are also vulnerable to high temperatures and bleach.

Bacteria do not like cold places; in fact, a few years ago scientists found ancient bacteria and viruses frozen in Siberian ice. The cells were unable to multiply but were incredibly well preserved.

The fight against viruses and bacteria

Now that we understand what bacteria and viruses are, it’s time to look at what science is doing to address the problems they are causing in our world.

Thanks to the events that began in 2019, we as a society are more informed about bacteria and viruses than ever before. We have learned a lot about how to prevent their spread. We have better understood how viruses evolve and spread. And we have seen one of the fastest vaccine developments in history.

As we have already said, viral and bacterial infections must be treated differently. And these treatments vary greatly within species.

Let’s take a closer look at how we fight viruses and bacteria.

Before we go any further, it is important to remember that there are both good bacteria and viruses. We don’t want to completely eradicate all viruses and bacteria, but we do want to attack the dangerous ones.

Treatment and drugs

In this section we will discuss the treatment of bacterial and viral infections once they have been detected.

There are many viruses and bacteria whose infections cannot yet be treated. However, every year scientists are testing and developing more treatments. So there is room for hope. A great example of this is smallpox, which used to kill about 400,000 people a year and infect more than 15 million. After the introduction of a vaccine worldwide in the 1970s, smallpox has been eradicated.

Medicamentos antivirales

It is possible to obtain both targeted antiviral drugs (developed to fight a specific type of virus) and broad-spectrum treatments that can target multiple viruses at once.

The development of antiviral drugs came about primarily as a result of the pressure on the medical community to treat people with HIV and AIDS. This research dramatically increased knowledge about viruses and their interaction with the human body.

Antiviral drugs that help treat HIV, CoronaVirus, Hepatitis B and C and Influenza A and B are now available.

Bacterial infections can be treated with antibiotics.

Bacterial infections are somewhat easier to treat. This is partly because we know more about bacteria and have been developing treatments for longer.

If you develop a bacterial infection, you will be given antibiotics to treat it. The infection should clear up within two weeks.

The use of antibiotics has very few side effects. However, doctors are careful not to prescribe them unless necessary, as society’s overuse of antibiotics can lead to the emergence of new antibiotic-resistant strains (such as MRSA)..


Viral infections are treated with antiviral drugs once the infection has developed, but it is possible to use vaccines to prevent the development of these infections.

The theory behind vaccination is that if you expose your body to a small amount of the virus, it will create antibodies to destroy that small amount. Your immune system remembers the virus and the next time you are exposed to it, it can release the antibodies again and kill the virus before it infects you.

Invented by Edward Jenner in 1796, vaccines have changed the face of medicine forever. Diseases that used to kill 100,000 people a year no longer exist. Scientists are now working on vaccines for all the world’s major viruses.

What are the worst viruses?


Now that we have learned what viruses are, how they work and how dangerous they can be, let’s look at some of the most dangerous viruses that exist today. We have also touched on some viruses that have been eradicated but which killed tens of thousands of people a year, but only a short time ago.

Marburg virus

Marburg virus is an untreatable disease that can be contracted through exposure to some forms of fruit bats. It can also be spread from person to person through fluid exchange activities, such as unprotected sex or contact with broken skin.

Once infection has occurred there is no treatment for Marburg virus, however, studies have shown that treating the symptom of dehydration can increase the chances of survival. Symptoms of Marburg virus include internal bleeding, fever and severe dehydration. Many of its symptoms mirror those of Ebola.

Studies have shown that the mortality rate of Marburg virus ranges from 23-90%.

Ebola virus

The Ebola virus has symptoms very similar to those of the Marburg virus (haemorrhage, fever, dehydration). In the last decade, we have seen severe outbreaks of Ebola virus in West Africa, resulting in tens of thousands of deaths.

The Ebola virus has a mortality rate of 25-93%. In developed countries there is about a 50% chance of survival. It can also be transmitted from fruit bats to humans, and from person to person through the exchange of bodily fluids. There is no approved treatment for Ebola virus.


Rabies causes about 57,000 deaths a year worldwide. Symptoms include fever, paralysis, excessive salivation, hallucinations and falling into a coma.

There is a vaccine against rabies, and many countries around the world recommend vaccination before visiting them. The best known source of rabies is rabid dogs. But there are also some other animals that can infect humans, such as certain bats in Australia.


HIV (human immunodeficiency virus) is a virus that cannot be cured. If left untreated, HIV can develop into the much more deadly AIDS (Acquired Immune Deficiency Syndrome). Once someone develops HIV, they will have it for life. Although there is no cure for HIV, in recent years treatment has been developed to control the virus.

AIDS and HIV attack the immune system, creating an environment in which cancers and deadly viruses can thrive. Without treatment, the average person only survives with HIV for 8-9 years.


200 years ago, smallpox killed more than 400,000 people a year. Smallpox was one of the first viruses for which a vaccine was developed. The last naturally occurring case of smallpox was in 1977, and in 1980 the WHO declared the virus eradicated worldwide. In 1967, before the introduction of the vaccine, the world still had 15 million cases of smallpox each year.

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