Introduction to viruses

A virus is a tiny infectious agent that lives inside other living things.

These living things are called hosts. A virus cannot divide like a normal cell does. Instead, it must go inside a host cell to work. Once inside, the host cell is forced to make thousands of copies of the virus. These new viruses are built right inside the host cell.

Viruses are much smaller than bacteria. Most are only 20 to 300 nanometres in size. You would need 33,000 to 500,000 of them to stretch across just one centimetre.

Most viruses are made of just two or three parts. All viruses contain genes, which are sets of instructions. These genes are made of either DNA or RNA. To keep these genes safe, the virus uses a protein coat called a capsid.

Some viruses also have a bubble of fat called a viral envelope. This envelope helps the virus enter a new host cell. It also makes the virus easy to break with soap or alcohol. The shape of a virus can be simple or very complex. Some look like spirals, while others have many faces.

Scientists have studied viruses for a long time to understand them. In 1884, Charles Chamberland made a special filter to catch bacteria. In the 1890s, Dmitri Ivanovsky used this filter to study tobacco plants. He found that something smaller than bacteria could still cause sickness. Later, Martinus Beijerinck saw that these agents only multiplied inside living cells. He called them a "contagious living fluid."

In 1931, the electron microscope was invented. This allowed scientists to see actual images of viruses for the first time.

Viruses spread in many different ways depending on their type. Some viruses, like influenza, spread through the air in tiny moisture droplets. This happens when people cough or sneeze. Other viruses, like norovirus, spread through contaminated food or water. Some viruses are carried by insects, such as the dengue virus.

Viruses can also mutate, which means they change into new types. This happens very fast in viruses made of RNA. These changes can lead to pandemics, like the swine influenza in 2009. This is why we often need new vaccines for some viruses every year.

Even though viruses can cause disease, our bodies have ways to fight back. In healthy people, the immune system usually clears the infection. This can even give a person lifetime immunity to that specific virus.

Antibiotics do not work on viruses because they only fight bacteria. Instead, doctors use antiviral drugs to treat serious infections. Scientists also use vaccines to help prevent people from getting sick. Learning about viruses helps us understand how to stay healthy in a world full of tiny living things.