10 Characteristics of Virus, its Classification, Transmission and Infection

We explain what viruses are, their morphology, and the infection process. In addition, its characteristics, classification, and mode of transmission.

What are viruses?

Viruses are a kind of microscopic and acellular parasitic agents (which are not made of cells ), capable of reproducing only inside a host cell, generally using their genetic replication mechanisms and causing damage in the process.

Viruses  are capable of infecting any form of life , from animals and plants to bacteria and other viruses (virophages), and they exist in all terrestrial ecosystems, being the most abundant known biological form: more than 5,000 virus species have been described since its discovery in 1899, but it is estimated that there could be millions of them.

The origin of viruses is uncertain , since there are various theories about it. Some suppose that they could have evolved from plasmids (free-living DNA fragments), and others that they could come from bacteria or other cellular organisms, despite the fact that their structure is much simpler than theirs.

What virologists do agree on is that these are very primitive organisms in the history of life , despite the fact that there are no viral fossil records. Known and preserved virus species date back no more than 90 years. On the other hand, viruses have an enormous capacity for mutation, which makes them highly adaptable and changeable

virus size

The size of most viruses is so small that they cannot be seen through a light microscope, although there are exceptions such as large viruses (called gyrus ) whose size is exceptional.

Virus morphology

Although viruses are enormously diverse in their shape and structure, they are typically about 100 times smaller than bacteria and consist of a DNA molecule wrapped in a protein capsule . There are four possible forms of viruses:

• Helical. Helix-shaped, with a hollow central cavity where the genetic material (RNA or DNA) is housed.
• Icosahedral. Almost spherical, symmetrical, they are the most abundant of all those that infect animals.
• Envelope. These viruses have a lipid envelope that they extract from the same cell membrane of their victims. That same layer is used to inoculate its genetic material into the cell.
• Complexes. Viruses with complex shapes can be half icosahedral, half helical, and even have additional structures, such as protein tails. In many cases, these "tails" are used as a syringe to inject the virus's genetic material into the cell.

virus infection

The virus reproduction process comprises various stages and takes place within the infected organism and specifically within certain types of cells (infectious selectivity). These stages are:

• Accession. Through various mechanisms, the virus attaches itself to the cell to be infected, after having identified it as propitious (it must have certain characteristics that guarantee the virus the replication of its genetic material).
• Penetration. The phase in which the virus enters the cell is called "viral penetration", either through membrane fusion or through specific organs to inoculate its genetic material into the cell.
• Replication. The genetic material of the virus forces the cell to synthesize the proteins that make up the virus, thus replicating the same original infectious form within it.
• Release. The infected cell dies, since the number of viruses synthesized inside it bursts its plasma membrane, releasing these infectious forms into the environment and thus perpetuating the cycle.

Classification of viruses

Several types of viruses have been identified according to the type of genetic material they possess and the replication method they use inside the cell:

• DNA viruses . As their name indicates, these viruses have DNA and need to make it reach the nucleus of the infected cell in order to give rise to the synthesis of their proteins. This type of virus can be, in turn:

  • double stranded With double-stranded DNA.
  • single stranded With single-stranded DNA.

• RNA viruses . Unlike the previous ones, they have RNA as genetic material and usually replicate in the cytoplasm of the cell, instead of its nucleus. Five subtypes can be identified:

  • double stranded With double-stranded RNA in its genome.
  • positive single strand. With single-stranded RNA, with a positive polarity that makes its replication simple and fast.
  • Negative single strand. With single-stranded RNA, but negative polarity, so it requires certain processes to become positive before replication.
  • Retrotranscribed single strand. With single-stranded RNA, but they replicate through reverse mechanisms: producing viral DNA from the RNA they possess.

life span of viruses

Viruses have a relatively short lifespan , since their entire existence is devoted to identifying and infecting suitable cells. However, viral infections can be transient or chronic, curable or fulminant.

Diseases caused by viruses

Diseases caused by viruses in man are abundant. They oscillate between temporary infections, which last as long as it takes for the immune system to control the presence of the virus and expel it from the body, and others that require treatment to eliminate or at least control the infection.

Throughout history there have been numerous pandemics of viral origin that have cost numerous human lives, such as chickenpox, Ebola, dengue or chikungunya fever .

Transmission of viruses

Viral transmission depends largely on the type of disease in question, and can be spread from one healthy individual to another , directly, through the exchange of fluids (sexual contact, blood transfusions or even through coughing and direct contact with infected skin); or indirectly, through an intermediary (a mosquito , a flea, an animal bite, etc.).

Treatment for viruses

Since viruses do not respond to antibiotics , in many cases the only possible treatment is rest and treating symptoms to avoid further complications. In other more severe cases, the viral infection requires medical treatment with retrovirals . Some viral infections cannot be cured outright, but rather kept at bay, at levels that are not dangerous and infective.

Viral technology

Many viruses can be used by human technology for a variety of purposes , ranging from pest control, biological weapons, or biological actors in the medical industry and nanotechnology. This is because they are relatively simple organisms, which can be engineered through laboratory-assisted evolution.

Are viruses living beings?

There is debate as to whether or not viruses are living things since they possess life-like characteristics (such as genetic material) and are dependent on living cells to synthesize their proteins, but they differ from even the most primitive bacteria in that they are infinitely simpler.

Furthermore, the logic of known life is based on the minimum unit of the cell, and viruses are not composed of them. That is why it is accepted that they are beings on the margins of life.

The above content published at Collaborative Research Group is for informational and educational purposes only and has been developed by referring to reliable sources and recommendations from technology experts. We do not have any contact with official entities nor do we intend to replace the information that they emit.