A microorganism that arisen in the city of Wuhan, China, in late 2019, spread across the world throughout 2020 and had the unimaginable ability, for most people, to paralyze the planet. But how was that possible? The new Coronavirus, which causes the Covid-19 infection, appears to have been at first transmitted from animals to people. The first cases were confirmed in a group of individuals who were in the same popular market in the Chinese city. There, several types of live wild animals were sold, such as snakes, bats and beavers, which could be sick and passed the virus onto people.
Since ancient times, humanity has dealt with epidemics that kill millions of people, such as the Black Death and the Spanish flu, two of the most lethal pandemics in history. However, there is a fundamental difference between these two epidemics: Spanish flu was caused by a virus and the Black Death was caused by bacteria.
Both viruses and bacteria are microorganisms, that is, visible only under the microscope.
Invisible to the naked eye, they quickly multiply in a short period of time and cause diseases, sometimes fatal, but they are completely different from a biological point of view. Bacteria are living organisms, composed of a single cell, which has everything they need to live: genome and cellular structures that produce protein, supplying them with energy. Thus, their simple metabolism is sufficient for them to multiply. Bacteria are not always harmful: some of them are vital to human health, such as those that compose the gut microbiota and aid the digestion.
Viruses are not cells; they are infectious particles. For many scientists, viruses are not even considered as living beings. They can multiply only with external help. They fundamentally need a host. Without them, they are just a lifeless protein coat with a genome. An infectious particle unable to divide or produce energy. But that particle only comes to life if it has the power to settle in a cell. When they infiltrate their genetic material in cells of other living beings, they reprogram them so that they produce viruses until they burst, thus releasing these infectious particles. Each virus has a specific host cell. Some of them attack only plants, others attack only animals and humans. There are also viruses that attack only bacteria and fungi.
Globalization, intensified in the last few decades, has facilitated the spread of viral and bacterial diseases, as it allows contact between people from all over the world in a short period of time.
Bacteria and viruses act similarly in the human body, by multiplying within our bodies and causing an immune system reaction. The difference is that viruses are more mutable, that is, they undergo more genetic changes and it makes them more difficult to find answers to the combat them. Mutations occur more frequently in viruses than in bacteria, since the former can store information not only in DNA (composed of two genetic strands), but also in RNA, simpler as a genetic load.
Viruses are the cause of epidemics and pandemics, such as that of the Coronavirus, and are responsible for countless diseases, such as AIDS, measles, hepatitis, H1N1, dengue, herpes, mumps and yellow fever. As for bacteria, diseases such as pneumonia, tuberculosis, tetanus, leptospirosis, gonorrhea, syphilis and leprosy are attributed to them.
Antibiotics act against bacteria only. Since viruses do not live, they cannot be killed. Against them, there are only antivirals, which inhibit the multiplication of these particles, for example, by preventing them from reaching host cells. Even so, doctors often prescribe antibiotics for viral infections as well, since viruses weaken the immune system, allowing bacteria to attack. The antibiotic is indicated to prevent that attack.
For both bacteria and viruses, it is possible to develop vaccines. Most vaccines work only as prevention, a response previously created to avoid a problem, not to combat it.
The emergence of antibiotics in early 20th century changed the way humanity would face epidemics caused by bacteria, as well as the implementation of basic sanitation. In general, antibiotics act in central cell processes, similar among the various types of bacteria. That is why the medicine has a spectrum and can be effective against a range of microorganisms. Over the years, resistance to the effectiveness of antibiotics has emerged, with the appearance of "superbugs".
With viruses, there is no clear action plan: as the genetic diversity is greater, it is difficult to create a drug that cancels replication, forcing the combination of several viruses: the so-called "cocktails".
Experts say there are some basic tips to prevent contamination by viruses and bacteria: keep homes and public places always fresh and clean; wash your hands, especially before meals; perform daily body hygiene; only consume food within the expiry date; always wash fruits and vegetables before consuming them and always drink fresh water.
However, the best way to avoid viral and bacterial diseases is the prevention through vaccines. Immunization stimulates the body to produce antibodies, proteins that form a defense system in the body against invaders that can be harmful to health. Vaccines are a very effective form of active artificial immunization. The World Health Organization (WHO) estimates that they prevent almost 6 million deaths worldwide each year. In Brazil, for example, polio has been considered eradicated by vaccination since 1990.
Vaccines are nothing more than the causative agent of the disease or fragments thereof introduced into the body in an attenuated manner. The dose of virus or bacteria present in the vaccine does not cause the disease, but it is enough to activate the immune system, attack the foreign agent and create immune memory. However, antibiotics and antivirals, due to the evolution of microorganisms, have not been able to extinguish many diseases.
Over time, viruses and bacteria become increasingly resistant to variations in existing drugs. Therefore, scientists always need to create new drugs and immunizers.
- Increasingly populous urban areas facilitate the spread of microorganisms. With such expansion, human being invaded the natural habitat of other animals, started to raise them on a large scale, coming into contact with the secretions of those animals. The viruses that infected cattle causing rinderpest, for example, mutated in humans to measles.
- Before the emergence of antibiotics, simple bacterial infections caused the death of thousands of people. It was only in 1928 that scientist Alexander Fleming discovered, by mistake, penicillin, an antibiotic used in the treatment of bacterial diseases to present days.
- In the 15th century, Venice, Italy, was the first city to put in place measures to contain diseases, such as closing borders and quarantines.
- Between the 19th and 20th centuries, tuberculosis and smallpox left more than 1 billion dead. The pandemic concept became stronger with the Spanish flu, almost 100 years ago.
- Then, HIV (AIDS) cases exploded between the 1980s and 1990s.
- Today, there are approximately 100 types of viruses that infect humans, compared to at least 50 species of bacteria capable of transmitting diseases.
- In mid-19th century, the Koch bacillus began to infect the population worldwide. The bacterium, which caused tuberculosis, killed, in 100 years, about 1 billion people.
- Between 1918 and 1920, the Spanish flu, caused by the influenza virus, killed between 50 and 100 million people worldwide.