A virus is a very tiny organism that can only live and reproduce inside another living cell. The cell the virus invades is called the host cell. The virus basically turns the cell into a factory to make more viruses which then invade more cells.
Viruses consist of a stand of genetic information ( DNA or RNA ) inside a protein shell called a capsid. Some viruses also have a membrane layer around them.
Viruses use cellular components of the host cell to reproduce. New viruses are then released from the host cell which then search for a new cell for themselves.
There are many different types of viruses which infect different hosts and have different structures. These play dough virus models are a great way to learn about viruses and their structures.
Examples of viral infections include
Common cold virus
HIV – Human Immunodeficiency Virus
What happens when you are infected with a virus
Some viruses release poisons which make you feel poorly.
The majority of the time the human body can fight the virus and any medical treatment is to relieve the symptoms of the virus rather than destroy it, but for more severe infections such as HIV and Hepatitis medicines called antivirals can be used.
Some viruses stay in your body for a very long time. Herpes Simplex Virus lies dormant until a person is run down when it activates itself leading to a cold sore. This is why people often get cold sores after another illness.
Chicken Pox – caused by varicella Zoster Virus can reoccur as shingles in adulthood.
How do viruses spread?
Viruses are very small and light and are passed between people by touch, through water or in the air.
How do humans fight viruses?
It’s all quite complicated but very simply, white blood cells in our blood engulf and destroy microbes that can cause us harm including viruses.
White blood cells produce antibodies to fight microbes. These often remain in the blood stream ready to fight the same infection again.
White blood cells neutralise poisons made by microbes.
Vaccines are available for some viruses which help us to become immune to the virus being vaccinated against.
Viruses are the smallest microbe ( 1/1000000 mm). Most viruses cannot be seen with an optical microscope.
Viruses cannot reproduce on their own they need a host cell.
The study of viruses is called virology and scientists that study viruses are called virologists.
Viruses are not classed as living things. They can’t reproduce or metabolise on their own.
The first human virus to be discovered was yellow fever virus in 1901 by US army physician Walter Reed.
Viruses don’t just infect humans, they infect plants, fungi and even bacteria!
A virus that infects bacteria is called a bacteriophage!
Viruses have no nucleus.