| A virus is a small pocket of the protein that | | | | lymphocytes, can recognize and kill cells containing |
| contains genetic material. If you put a virus with a | | | | viruses, like the surface of infected cells is |
| bacteria, virus would be dwarfed. For example, | | | | changed when the virus begins to multiply. Many |
| the polio virus is around 50 times smaller than a | | | | viruses, when released from the infected cells |
| Streptococci bacterium, which itself is only | | | | were eliminated effectively by the antibodies that |
| 0.003mm long. Viruses can be described as either | | | | are produced in response to infection or previous |
| RNA or DNA viruses, according to the type of | | | | immunization. |
| nucleic acid forms their core. | | | | Immunization against viral infection is not always |
| The four main types of viruses are: | | | | possible |
| * Icosahedral - the outer (capsid) is made from | | | | It is possible to vaccinate against many serious |
| 20 flat sides, which gives a spherical shape. Most | | | | viral infections such as measles, mumps, hepatitis |
| viruses are icosahedral. | | | | A and hepatitis B. An aggressive vaccination |
| * Helical - the capsid is shaped like a rod. | | | | campaign throughout the world, led by the World |
| * Wrapped - the capsid is enclosed in a baggy | | | | Health Organization (WHO), succeeded in |
| membrane, which can change shape but often | | | | eliminating smallpox. However, some viruses - |
| appears spherical. | | | | such as those causing the common cold - are |
| * Complex - the genetic material is covered, but | | | | capable of mutating from one person to another. |
| without a capsid. | | | | This is how an infection with essentially the same |
| The body's response to viral infection | | | | virus can evade the immune system to maintain. |
| Viruses pose a considerable challenge for the | | | | Vaccination of these types of viruses is difficult |
| body's immune system because they hide inside | | | | because the virus has changed its format for the |
| cells. This makes it difficult for antibodies to reach | | | | time vaccines have been developed. |
| them. Some special immune system cells called T | | | | |