Table of Contents

  1. What is Virus?
    • Transmission of Viruses
    • Contagious period after contracting a viral infection
    • Can the Virus evolve?
    • Types of Viruses
    • Some of the common viral diseases
  2. What is Bacteria?
    • Difference between a Virus and a Bacteria
    • Reproduction of bacteria
    • Survival mechanism of Bacteria
  3. Viruses and Evolution
    • Where did the Virus come from?
    • Progressive Hypothesis
    • Regressive Hypothesis
    • The Virus-First Hypothesis
    • How did Virus evolve
  4. Evolution of Bacteria
    • Classification of Bacteria
    • Key factors affecting the growth of bacteria
  5. Fighting the Viruses and Bacteria
    • Treatments and Drugs
    • Antiviral Drugs
    • Vaccines
  6. List of some of the worst Viruses
  7. Some of the dangerous bacteria troubling our society
  8. Conclusion


Everything you need to know about viruses and bacteria; evolution, how to fight them, and the worst of them!

What Is a Virus?

Different Viruses

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

Talking about viruses can get complicated because every virus 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 it comes to talking about viruses is that they affect various organisms differently. For example, Influenza C has a  near deadly effect on birds, but gives humans a mild cold. 

Viruses are the most abundant organism on the planet. They infect the host’s cells but do not replace them. Viruses cannot be cured, however, through vaccination and immunization their spread can be stopped. 


How do Viruses Transmission?

Viruses’ genetic purpose is to reproduce. They are ruthless and incredibly efficient at this task. The most ‘successful’ viruses have a high Rate of Transmission – for example, Covid-19 was believed to spread so quickly because it had an R rating of 1.4. This means that every person who caught it was likely to infect at least 4 other people. While Influenza has around a 1.1 rating. 

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

  • Touch 
  • Swapping of bodily fluids (saliva, blood, sweat, semen) 
  • Airborne pathogens (from sneezing and coughing
  • Contamination of food 
  • Insect bites  
  • Contaminated water 

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

The Incubation period is what scientists refer to as the time when the virus begins to reproduce in the host’s body. Some viruses show symptoms at this point, while others – like Rabies – don’t show any symptoms until it’s too late. 

How Long Is Someone Contagious?

The most successful viruses are contagious for a long time. The time that you are contagious after contracting a viral infection varies depending on the virus. 

For example, Chickenpox sufferers are still contagious 5 days after the spots first appeared. While people with CoronaVirus (SARS-CoV-2) are believed to be contagious up to 14 days after their symptoms first appear. Measles is contagious for around 10 days after the symptoms first appear. 

The real danger when it comes to viruses is that they are contagious before the first symptoms start to show. This is when they spread the most.  

Can The Virus Evolve?

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

When viruses make copies of themselves they do not always make exact copies. These mistake copies are referred to as mutations. AIDS frequently does this, as it makes over 1 billion copies of itself a day.  

Some mutations have a better survival rate than others or even the original virus. If this mutation survives, it starts to make its own copies. This is natural selection in its most basic form. 

Are There any Friendly Viruses?

Not all viruses are bad! In fact, our digestive system is full of friendly viruses. This type of partnership is referred to as a symbiotic relationship. The viruses have found that it is easier for them to survive by working with the host. 

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

Types Of Viruses

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

Arguably, one of the most common viruses is Influenza. Everyone one reading this article has probably had it at least once. Influenza is a fast spreading and fast evolving virus – 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 you develop as the result of contracting a virus. Here are some of the most common viral diseases: 

  • smallpox
  • the common cold and different types of flu
  • measles, mumps, rubella, chickenpox, and shingles
  • hepatitis
  • herpes and cold sores
  • polio
  • rabies
  • Ebola and Hanta fever
  • HIV, the virus that causes AIDS
  • Severe acute respiratory syndrome (SARS)
  • dengue fever, Zika, and Epstein-Barr

What Is Bacteria?

Diffrent types of Bacteria

Bacteria are single celled organisms. Their cell structure is a lot simpler than the average cell in the human body. Most notably they have no nucleus (the ‘brain’ of the cell). Instead they contain a single loop of DNA.  

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

  • spherical (cocci) 
  • rod (bacilli)
  • spiral (spirilla)
  • comma (vibrios)
  •  corkscrew (spirochaetes

For every cell in the human body, we contain around 10 bacteria. The majority of these can be 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 great way to build immunity

What Is The Difference Between A Virus & Bacteria?

Bacteria are living cells, they are an organism in their own right. They do not rely 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 do we need to be able to tell the difference between bacteria and viruses? 

Well, because they are so different they need different treatment when they start to cause us trouble. Doctors want to make sure that they are only prescribing antibiotics when it is necessary – as getting this wrong can lead to more antibiotic-resistant super strains developing. 

How do Bacteria Reproduce?

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

Binary fission is the process of a single cell organism diving itself into two. These two cells are exactly the same. 

This may sound like a slow process, but take a look at this E Coli case study. 

If the conditions are right (warm and wet) within 7 hours 1 cell can turn into 2,097,152 bacteria. Give those guys another hour and there will be 16,777,216 of them. Scary stuff. 

Bacteria’s Survival Mechanism

As well as being able to reproduce at impressive rates, Bacteria need other tactics  to survive. Some bacteria form an endospore. 

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

Viruses and Evolution

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

Where Did 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 for the origins of viruses. And there is no one universally agreed upon theory. 

The three theories are 

  • The progressive theory 
  • The Regressive theory 
  • And the Virus-First theory 

Continue reading to find out more about each of these theories. 

Progressive Hypothesis 

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

Both use coded RNA to replicate themselves whenever they enter a new cell. They also use a similar method for entering and exiting cells. It is believed that viruses learnt from or evolved from these retrotransposons. 

Regressive Hypothesis 

This hypothesis infers that viruses came into being thanks to a reductive process. This theory claims that eukaryotic genomes and Rickettsia prowazekii have enough DNA in common to prove that they have a common ancestor. 

This theory therefore suggests that viruses have complex ancestors that were living creatures, possibly even bateria. Through a reductive evolution process they have become the cell invading system they are now.

The Virus-First Hypothesis

This theory differs from the other two as it does not assume that cells existed before viruses – hence the name, The Virus-First Hypothesis. 

It has been suggested since 2005 that viruses were the first reproducing entity, and that they existed in the pre-cellular world. This would make them the oldest form of ‘life’ we know of. 

The theory suggests that cells as we know them grew out of mutated viruses. They developed their nuclei and became more complex than their forefathers. 

How Did Viruses Evolve?

There is no agreed upon origin of the virus. And the answer might actually be more complex than a single correct theory. 

There are such a wide and varying variety of viruses across the world that some scientists have suggested that viruses could have evolved separately in multiple ways. This theory is mirrored in wider evolution, where we see creatures evolving 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 came into being through regressive processes. With the Virus-First theory still holding weight. 

Evolution of Bacteria

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

As we have mentioned above, Bacteria (as well as viruses) evolve quickly. It is one of the key elements of their survival. 

Classification Of Bacteria

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

  • spherical (cocci) 
  • rod (bacilli)
  • spiral (spirilla)
  • comma (vibrios)
  •  corkscrew (spirochaetes

Bacteria can be found in nearly every part of the world. They live in the air, the soil, in the Antarctic, and even inside us. 

What Factors Affect Bacterial Growth?

The more you understand 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 
  • Salt and Ion availability
  • Gaseous concentration 

Bacteria thrive well in warm, wet environments – like food left out at room temperature for too long. They also avoid direct sunlight as UVB rays can kill them. They are also vulnerable to high temperatures and bleach. 

Bacteria don’t 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. 

Fighting The Viruses & Bacteria

Fighting The Viruses & Bacteria

Now that we understand what bacteria and viruses are, it’s time to look at what sciences are doing to tackle the issues they are causing in our world.

Thanks to the events that began in 2019, as a society we are more educated about bacteria and viruses than ever before. We have learnt so much about preventing their spread. We have got a better understanding about how viruses evolve and spread. And we have seen one of the fast developments of a vaccine in history.  

As we touched on above, viral and bacterial infections need to be treated differently. And these treatments vary greatly within the species. 

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

Before we take a deep dive, it is important to remember that there are both good bacteria and viruses. We do not want to completely eradicate all viruses and bacteria, but we do want to target the dangerous ones. 

Treatment and drugs

In this section, we are going to talk about the way bacterial and viral infections are treated once they have been caught. 

There are many viruses and bacteria who’s infections cannot be treated yet. However, every year scientists test and develop more treatments. So, there is room for hope. A great example of this is smallpox – which used to kill around 400,000 people a year, and infected over 15 million. After a world wide vaccine roll out in the 70s, smallpox has now been eradicated. 

Antiviral Drugs

It is possible to get both targeted antiviral drugs (these have been developed to fight one specific type of virus), or broad spectrum treatments that can target multiple viruses at once. 

The development of Antiviral drugs mostly happened as the result of the pressure the medical community were under to treat people with HIV and AIDS. This research drastically increased the amount we understand about viruses and how they interact with the human body. 

It is possible to get Antiviral drugs that help treat HIV, CoronaVirus, Hepatitis B & C, and Influenza A&B.  

Bacterial infections can be treated with antibiotics

Bacterial infections are slightly easier to treat. Partly because we know more about bacteria and have spent longer developing treatments. 

If you develop a bacterial infection you will be given antibiotics to treat it. These should clear the infection within 2 weeks. 

There are very few side effects of using antibiotics. However, doctors are careful not to prescribe them unless necessary, as too much societal use of antibiotics can lead to new antibiotic-resistant strains (like MRSA) developing. 


Viral infections are treated with antiviral drugs once the infection has developed, however 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 this tiny amount. Your immune system remembers the virus and 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, vaccinations have changed the face of medicine forever. Diseases that used to kill 100,000s of people a year no longer exist. Scientists are currently working on vaccinations for all the major viruses in the world today. 

What Are The Worst Viruses?

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 around at the moment. We have also touched on a few viruses that have been eradicated but killed tens of thousands of people a year but a short time ago. 

Marburg virus

Marburg virus is an untreatable disease that can be caught by exposure to some forms of fruit bat. It can also be spread from person to person through fluid sharing activities like unprotected sexual intercourse or touching broken skin. 

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

Studies have shown the fatality rate of the Marburg virus to be anywhere between 23-90%

Ebola virus

Ebola virus has very similar symptoms to the Marburg virus (hemorrhaging, fever, dehydration). In the last decade, we have seen serious Ebola Virus outbreaks in Western Africa, resulting in tens of thousands of deaths. 

Ebola Virus has a fatality rate of between 25-93%. In developed countries there is around 50% can of survival. It can also be passed from fruit bats to humans, and from person to person through the exchange of bodily fluids. There is no licensed Ebola virus treatment.   


Rabies causes around 57,000 deaths a year across the globe. Its symptoms include fever, paralysis, excessive salivation, hallucinations, and falling into a coma. 

There is a rabies vaccination, and there are many countries around the world that recommend getting this vaccination before visiting. The most commonly known source of rabies is rabid dogs. But there are also a few other animals that can infect humans, including certain bats in Australia. 


HIV (human immunodeficiency virus) is a virus that has no cure. When not treated HIV can develop into the much more deadly AIDs (acquired immunodeficiency syndrome). Once someone develops HIV they will have it for life. While HIV cannot be cured, in recent years a treatment has been developed to control the virus.

AIDs and HIV attack the immune system, creating an environment where cancers and deadly viruses can thrive. Without treatment the average sufferer only survives with HIV for 8-9 years. 


200 years ago Smallpox killed well over 400,000 people a year. Smallpox was one of the first viruses to have a vaccine developed for it. The last naturally occurring Smallpox case happened in 1977, and by 1980 WHO declared the virus eradicated across the globe. In 1967, before the vaccination rollout,  the world was still witnessing 15 million smallpox cases a year.  


Hantavirus is a virus that is almost entirely contracted after inhaling rodent feces. Until 2019 human to human transmission was not thought possible until a case was recorded that year in South Africa. 

Symptoms of Hantavirus strains include a fever, abdominal paints, bleeding under the skin followed by a drop in blood pressure. In many cases the disease is fatal. 


It is believed that there are over a thousand variants of Influenza that fall under 4 main categories – A, B, C, and D. Between 3-5 million cases of Influenza are recorded a year among humans – with 650,000 deaths occurring annual due to the virus. 

There are annually updated Influenza vaccinations, as at least one new and potent strain appears every year. Some of the strains can pass across species – the 2009 Swine Flu epidemic is a good example of this. 


Dengue (fever) is a mosquito-borne virus that kills around 40,000 people every year. With around 390 million cases being recorded every year. The most common preventative treatment for Dengue fever is mosquito nets. There is a vaccine, but it is only approved for use on people who have already had the virus. Re-infection is possible and highly likely in places with high mosquito populations.  


Discovered in 1973, Rotavirus infects nearly every child in the world at least once before the age of 5. It traditionally causes severe vomiting and diarrhea in the first infection. With each subsequent infection it gets less impactful. 

Rotavirus is most dangerous in children under 2 and people of any age with immunodeficiencies. 


SARS-CoV ( or Severe Acute respiratory syndrome coronavirus) is a strand of corona virus that attacks the epithelial cells of the lungs. 

An outbreak of SARS-CoV in South Asia in 2003 led to laboratories in the area working for WHO to establish coronavirus as the cause of SARS. A new strain of SARS-CoV, SARS-CoV-2, is what caused the new coronavirus outbreak that began in 2019. 

The fatality rate of SARS-CoV is around 9%, but does rise to 50% in the over 60s. Once of the major dangers of SARS-CoV is that it makes the sufferer more vulnerable to bacteria like pneumonia. 


MERS-CoV (or Middle East respiratory syndrome–related coronavirus) is a strain of coronavirus that is the cause of MERS. This strain of corona virus can infect humans, camels, and bats. 

In 2019 858 of the 2,494 people who caught MERS-CoV died. This number shocked scientists who had previously estimated the fatality rate of this disease as under 30%. 

MERS-CoV was first discovered in 2012, and since then has spread to over 21 countries. It is one of the viruses on WHO’s watchlist for viruses that may cause future epidemics.

What Are The Worst Bacterias?

The Worst Bacterias

In the final section of our history of Viruses and Bacteria, we are going to look at the most dangerous bacteria troubling our society this year. 


First visualized in 1880, Salmonellae is one of the leading causes of food poisoning in the US today. Studies suggest 98.4 million salmonellae infections occur every year, affecting 11% of the world’s population. 

It is also believed that between 60-80% of global Salmonella cases go unrecorded, so the infection rates could be much, much higher than they appear. 

Salmonella infections usually cause vomiting and diarrhea. 

Helicobacter pylori

Helicobacter pylori is a highly contagious bacteria that was first identified in 1982. Scientists believe 50% of the world has Helicobacter pylori in its intestines. While 90% of people infected with Helicobacter pylori never experienced any complications, for those who do it can be very serious. 

For the people who have complications from Helicobacter pylori, 20% of them develop stomach and intestinal ulcers. Helicobacter pylori has been linked with many other diseases like Ahlizemers and Cancer. 


Discovered in 1936, Enterobacteriaceae are a large family of bacteria with over 100 strains. Many of which are natural parts of our gastrointestinal biome. While others live underwater, in soil, in animals, and even in parasites. 

While Enterobacteriaceae are not dangerous in their own right, more nasty bacteria like Salmonella rely on them to survive. 

Campylobacter spp

Campylobacter spp is another vicious bacteria that causes substantial food poisoning incidents across the world every year – the CDC suggesting numbers up to 1.5 million cases a year. 

Unlike other bacteria, Campylobacter spp is not known for causing outbreaks, rather individual cases. 

Neisseria Gonorrhoeae

Neisseria Gonorrhoeae was discovered in 1879 and is the bacteria that causes the sexually transmitted disease Gonorrhea.

The bacteria is spread through physical contact during oral, vaginal, and anal sex. It is possible to prevent infection using protection that adequately covers the genitals.  

Gonorrhea is very effective at avoiding the human’s immune defenses, and it is possible to get re-infected multiple times.  

Pseudomonas aeruginosa

The most common issue that Pseudomonas aeruginosa is responsible for is the development of pneumonia in humans. Pneumonia can be developed if the person’s lungs are infected by Pseudomonas aeruginosa. It is not just humans who are susceptible to pneumonia. In some cases, pneumonia can be fatal. 

Pseudomonas aeruginosa has also been recorded to cause infections in the blood, heart, and kidneys. These infections can also be fatal. 

Enterococcus faecium

Enterococcus faecium is a slightly complex bacteria that can coexist in the intestines of humans or animals. However, in some cases, it can cause meningitis – which can be fatal, particularly when caught by children. 

This is a fast evolving strain of bacteria and those who are vulnerable to meningitis should be vaccinated against new strains every autumn. 

Staphylococcus Aureus (MRSA)

MRSA was one of the first ‘super bugs’. Given this nickname, because they developed immunity to several of the major antibacterial treatments – most notably Penicillin

Most cases of MRSA infection occur in the hospital. It is very contagious and can be spread via touch or contamination of medical equipment. MRSA can be treated by antibiotics, but only by a few specialist types. 

Acinetobacter Baumannii

Acinetobacter Baumannii targets humans with compromised immune systems (many people who suffer from allergies or autoimmune issues). It is not known where Acinetobacter Baumannii originated from. However, it can cause fatal consequences in humans. 

Acinetobacter Baumannii can cause Meningitis, pneumonia, bloodstream infections, urinary tract infections, and even infect open wounds. Compromised immune systems are often unable to fight back against these infections. 


A Virus and a Bacteria side by side

Viruses and bacteria are very different. Bacteria are single celled organisms that can survive outside a host. Viruses rely on their hosts for survival, they are not technically alive because of this. 

Despite their differences they can both be deadly. Bacterial and viral infections kill millions of people around the world every year. As science develops new treatments and learns more about the human body these numbers will drop. 

The world is also full of good viruses and bacteria. Our digestive system would not be able to function without them. We even have viruses in our body who have a symbiotic relationship with our immune system. These viruses kill some of the deadliest bacteria that enter our bodies.