What are the 5 characteristics of viruses?

16 Nov 2022
Stefano Mirabello
Stefano Mirabello
Medical Writer

Did you know that viruses are not alive? Despite this, they can be very dangerous. In fact, viruses are responsible for causing some of the deadliest diseases known to man. Knowing some characteristics of viruses is useful as it helps you understand why certain treatments may be required or what precautions should be taken during an outbreak. In this blog post, we will discuss five characteristics of viruses.

1. Non-living

Viruses are small infectious agents also known as pathogens. They are not living organisms and can only grow when they’re in contact with living cells. Viruses are not made of cells and they lack many of the cellular organelles found in other living organisms. They can’t divide on their own and need an external force for sustenance, like host animals or plants who provide them nutrients while there’s no oxygen available (this is what gives viruses life). The virus only comes alive when it envelops its genetic material in cells of other living things so that’s why some viruses attack plants while others only affect animals or humans. Once inside the cell, they use the cell’s energy, ribosomes, enzymes, and other cellular parts to replicate.

2. Size and Shape

Viruses are microscopic and invisible to the naked eye. Viruses are 10 to 100 times smaller than the smallest bacteria. Viruses were among the first biological structures to be studied when the electron microscope was developed in the 1930s. This allowed scientists in the field of microbiology and virology to study microbes in much more depth.

Viruses come in a wide variety of shapes and sizes, from simple spherical particles to more complex structures. The shape of a virus is determined by the proteins that make up its capsid or outer shell. The capsid is composed of numerous subunits called capsomeres, which are arranged in a specific pattern.

The most common shapes are icosahedral (20-sided), cylindrical, and helical. Icosahedral viruses are often spherical, while cylindrical viruses are rod-shaped. Helical viruses resemble spirals or coils. The shape of a virus can affect its ability to infect cells and replicate. For example, the cube-shaped virus has surface proteins that allow it to attach to cell walls. Once attached, the virus can then inject its genetic material into the cell and begin replicating.

In contrast, the star-shaped virus uses long, spiky proteins to puncture cellular membranes. This allows the virus to directly enter the cell, where it can then hijack the cell’s reproductive machinery to create new copies of itself. While different in form, both of these viruses are highly effective at achieving their goal of replication. Therefore, understanding the different shapes of viruses is important for developing effective treatments and prevention strategies.

3. Virus structure

Viruses are small infectious particles that can reproduce only inside the cells of other organisms. A virus is composed of:

  • A protein coat called a capsid, surrounds a core of viral genetic material. The capsid is assembled from protein subunits, called capsomeres
  • A core of a virus contains nucleic acid: either DNA or RNA, depending on the type of virus. A virus is called either a DNA virus or RNA virus. The viral genome encodes the genetic information needed to produce new viruses
  • An outer lipid-protein layer of the membrane is called the envelope but it is not a universal feature

The protein shell and viral genome are together known as the virus particle or virion. Once a virion has entered a host cell, it hijacks the cell’s machinery to produce new viruses. These new viruses then travel to infect other cells, leading to the spread of infection.

Viruses can also attack bacteria. The viruses that infect bacteria are known as bacteriophages or phages and can vary in structure. They are harmless to humans, animals or plants and only attack bacteria.

4. Reproduction/Life Cycle

There are two processes used by viruses to replicate: the lytic cycle and the lysogenic cycle. All viruses are unable to replicate on their own. They need living hosts such as the human body, plants or animals. They have to enter a living cell of a host and take over the cell’s processes for making new genetic material and proteins. The cell copies the viral genetic material and makes new viral genetic material and proteins. These components assemble into new viruses, which escape from the cell. Some types of viruses cause the complete breakdown of the cell. Other types of viruses leave by pushing through the cell membrane. Both methods damage the cells and this causes disease as the host then begins to replicate the viral DNA. The viruses that have left the cell can go on to infect other cells.

5. Causes diseases

Viruses cause a wide range of diseases in plants, animals, and humans.


Some human viruses are the herpes virus which causes chicken pox and cold sores, and the adenovirus causes the common cold. The coronavirus causes severe acute respiratory syndrome (SARS) and the influenza virus is responsible for the yearly flu epidemic.


Some crop diseases are the tobacco mosaic virus which can cause yellowing and necrosis in tobacco plants, the turnip yellow mosaic virus, the tomato bushy stunt and the tomato spotted wilt virus. The striped appearance of some tulip varieties is caused by a virus. Plant viruses are generally RNA viruses.


Some important animal diseases caused by animal viruses are foot-and-mouth disease in cattle, swine fever, fowl pests and myxomatosis in rabbits.

Most viruses are host-specific, meaning they can only infect a certain type of organism. For example, the influenza virus can only infect humans, while the tobacco mosaic virus can only infect tobacco plants.

Viruses are small infectious particles that can cause disease. Most viruses are spread through contact with respiratory secretions, such as saliva, mucus, or blood. Some viruses are spread through contact with contaminated surfaces, such as doorknobs, countertops, or communal items such as towels. Other viruses are spread through contact with infected animals, such as bats, birds, or pigs. Others are transmitted through mosquito bites.

There is no cure for viral infections: antiviral drugs can be used to treat viral infections and some viruses can be prevented with vaccines. Vaccines work by injecting a person with a small amount of the virus, which then triggers the immune system to create antibodies to the virus. These antibodies help protect the person from future infection. There are many different types of viruses, and each one can cause different diseases. However, all viruses share one common trait: they can all cause illness in plants, animals, and humans.

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