Viral diseases

• Viruses are tiny, non-living (do not have cells) particles that can reproduce rapidly within the body.
• 1. To survive and replicate, they invade host cells (animals or plant cells).
  2. The virus particle inserts its own DNA into the host cell’s DNA, which is then copied and used to make more viruses.
  3. Once the new virus particles have been synthesised (made), they cause the cell to burst. This releases the new viruses to invade more cells.
  4. This cell damage makes us feel ill.
• Measles

  • Symptoms include a fever and red skin rash.
  • Measles is a virus that can be fatal if complications arise.
  • For this reason, most young children are vaccinated against measles.
  • The measles virus is spread by breathing in (inhaling) droplets from sneezes and coughs.
• HIV (Human immunodeficiency virus)

  • HIV is spread by sexual contact or the exchange of body fluids (e.g blood from sharing needles).
  • Initially, HIV causes a flu-like illness. However, unless antiretroviral drugs are used successfully, the HIV virus enters the lymph nodes and attacks the body’s own immune cells.
  • AIDS is caused by HIV. It is the name given to the life-threatening infections that can happen when a person’s immune system has been badly damaged by HIV.
• TMV (Tobacco mosaic virus)

  • Tobacco mosaic virus (TMV) is a pathogen that affects plants, such as tomatoes.
  • The unique ‘mosaic’ pattern of the discolouration of the plant stunts the growth of the affected plant, because photosynthesis cannot take place.