Viruses are an entity that can be intriguing to anyone, even scientists who have studied very carefully about them. The virus is a headache to all biologists, because some people believe that the virus cannot be a true living organism, some say it is possible.
But the truth is that viruses do not belong to any of the three groups of living things: from ancient bacteria, bacteria to eukaryotes (plants, animals, fungi, etc.). They are extremely small in size, only from a few dozen to a few hundred nanometers long.
Clearly, the virus is a lot smaller than bacteria, and is only about one-tenth the size of a human blood cell. That means you can’t even detect most viruses with an optical microscope.
Only a few dozen to a few hundred nm in size, the virus can only be seen under an electron microscope.
At this extremely small size, the virus has an extremely minimal structure. Its minimalism has reached the point where no virus appears to act as a living cell.
Looking inside the complete virus, you usually see only one form of genetic material, be it DNA or RNA, surrounded by a layer of protein called capsid. Sometimes, viruses may coat a layer of fat, but are borrowed from the host cell.
Because the structure is so minimal, viruses do not have ribosomes, so they cannot make proteins and reproduce themselves. The virus needs to break into the host cell, gaining control of metabolism to multiply.
The over-reliance on host cells pushes the virus to the limits of the definition of life. Some scientists say viruses live, but others will have the basis to say they are just inanimate entities.
1. Has the virus evolved from inanimate molecules or evolved from bacteria?
There are many competing theories explaining virus evolution. One of them said that the virus was a descendant of an ancient lineage. This creature once had a cellular life. But like viruses, they live parasites in other cells.
Over time, they may have realized that if they lived such a parasitic life, there would be no need for organelles. The virus ancestor simplified itself and became the virus now. So the virus may have evolved from a living organism.
But there is another theory, suggesting that viruses were originally genetic agents that had no place in the genome. Because of that, they move around, hanging around and out of cell confinement.
At that point, it could be related to transposition elements, or jumping genes. These genes can be copied or cut off from a genome. They then attach themselves to other parts of the DNA.
If so, then it is likely that the virus is only the result of a molecular accident then stabilized during evolution. It also means that the virus has never been, in the past and present, a complete living being.
2. How does virus invade host?
Because of their simple structure, viruses cannot move or even reproduce outside the host cell. In order to survive, they must search for a parasite host to spread and multiply.
Viruses correctly identify their hosts by surface receptors, matching the ideal cell that they evolved to infect. After using these receptors as a ticket to sneak inside a cell, the virus will gain access to the genetic material inside it, the DNA, to gain control of the entire cell. After that, the virus will freely manipulate, causing the organelles to work for it, naturally its RNA and proteins millions of times.
According to estimates from a study in the mBio journal of the American Society of Microbiology, mammals are currently the reservoir for at least 320,000 different virus species. Expanding to the vertebrate species, we have more than 3.6 million other virus species. And if you include invertebrates, plants, lichens, fungi and algae, the number could be more than 100 million.
That is not to mention the bacteriophages, which are viruses that infect bacteria and unicellular organisms. Scientists estimate the amount of phage in the oceans can be as high as 10thirty first.
3. The path of spread of the virus
Inside the host cell, the virus can make a large number of copies and continue to infect other cells. For example, if you have the flu, your body will become a machine that produces hundreds of trillions of viruses in just a few days, 10,000 times more people on Earth.
How a virus can spread from person to person depends on the strain and the situation. Many viruses can be easily spread through the respiratory tract, in other words in the same atmosphere you breathe with an infected person.
Large numbers of viruses can travel as far as 4 meters when a person sneezes or coughs. They are transmitted through a cloud called “aerosol“, containing the carrier fluid in which the patient’s body fluids and the virus are contained.
Also in these body fluids, the virus can be spread through contact, when the patient does not wash his or her hands often, he / she can spread the virus he has through handshakes and through intermediaries. when both of them touch like a table, doorknob, lift button …
Some other viruses spread through blood, stool or vomit, such as Ebola. Unlike many other viruses, scientists think that Ebola cannot spread through the air after people infected with the virus cough or sneeze.
Disease vectors like mosquitoes can also become a “taxi trip “ Give the virus hitchhike from person to person. A good example is dengue virus, which causes dengue, Zika, Chikungunya and West Nile viruses.
4. What happens if the virus evolves?
When the virus spreads, it can take some of the host’s DNA and take it to a cell or another organism. Interaction with this host’s DNA can cause the virus to evolve and mutate.
We know some viruses that previously infect only animals, they are called zoonoses. But if a zoonoses accidentally get into the human body, and they take some human DNA, the virus can evolve into a new type that can infect us, and then spread from person to person.
Deviation spread occurs at very very low frequency. But once it happens, it becomes catastrophic. Most pandemics of the world, from HIV, avian flu to Ebola, Zika and most recently the acute pneumonia epidemic in Wuhan, have been animal-based.
Scientists say that in a group of viruses capable of transmitting animals to humans called zoonoses, the number of unknown strains can reach 1.67 million. Scientists currently classify only about 600 zoonoses of virus that infect animals.
5. Diseases and pandemics caused by viruses
When infecting humans, viruses are like hijackers, they invade functional cells and use those cells to multiply, creating new copies that resemble them. The process interrupts the cell’s activity, and the virus directs the cell to spend all the resources it has, including energy and proteins, to multiply new viruses.
Normal healthy cellular activities therefore stall and cause organ dysfunction. When the virus multiplies to a sufficiently large number, they cause the host cell to explode, dispersing a huge amount of virus that continues to infect new cells, creating a chain collapse effect that makes you sick and sick. .
The viruses usually attack certain cells in your body such as the liver, respiratory system, blood or nervous system. In the process, they cause many diseases, including smallpox, the common cold and flu, measles, mumps, rubella, chicken pox and shingles, hepatitis, herpes, polio. , rabies, Ebola and Hanta, HIV / AIDS, Severe acute respiratory syndrome (SARS), dengue fever, Zika and Epstein-Barr …
Some viruses, such as the human papilloma virus (HPV), can lead to cancer.
From past to present, mankind has witnessed many diseases and pandemics caused by viruses. For example, the Russian Flu pandemic (1889-1890) caused by H2N2 or H3N8 viruses killed about 1 million people, the Spanish Flu pandemic (1918) killed 50 million people, and the Asian pandemic (1956- 1958) caused by H2N2 virus killed 2 million people, Hong Kong flu caused by H3N2 virus killed 1 million people, HIV / AIDS pandemic (1981-present) killed 36 million people.
6. How does the body fight viruses?
When our immune system detects an invasive virus, it begins to respond to protect the body in order to keep the cells alive. A process called RNA interference breaks down genetic material of the virus, thereby killing and destroying them.
The immune system also makes special antibodies that can attach to the virus, thereby preventing them from spreading and entering new cells. Meanwhile, T immune cells are mobilized to destroy viruses floating in the blood stream.
Most viral infections trigger a protective response from the body’s immune system, only some viruses such as HIV and neurological viruses can hide from the immune defense system.
Neurological virus infects nerve cells. They are responsible for diseases such as polio, rabies, mumps and measles. Neurological viruses can affect the structure of the central nervous system (CNS) even when the patient has recovered.
7. Antiviral drugs and vaccines
We know that bacterial infections can be treated with antibiotics. But antibiotics are not effective in treating viral diseases. For these diseases, we can only vaccinate them to prevent them in the first place, or treat them with antiviral drugs.
Antiviral drugs were originally developed to deal with the AIDS epidemic. These drugs do not kill pathogens, but they inhibit the growth of viruses and slow their replication.
Currently, we have many antiviral drugs to treat certain diseases including herpes simplex, hepatitis B, hepatitis C, influenza, shingles and chicken pox.
But for some new strains, sometimes we only have drugs that help relieve symptoms. What to do is simply wait for the patient’s immune system to destroy the virus. Or, in the worst case, preventing secondary infections from happening could kill the patient.
Having said that, getting vaccinated is still the cheapest and most effective way to prevent viruses. Some vaccines have successfully eliminated and eradicated deadly diseases in the past, such as smallpox.
For emerging virus strains today, pharmaceutical companies usually only take 3-6 months to produce a vaccine against it. However, if we anticipate the epidemic and conduct research before it even breaks out, humans will have a full range of vaccines to prevent it from happening before it even happened.