B5: Communicable Diseases


B5.1: Health and Disease

  • health is a state of physical and mental wellbeing.
  • diseases, both communicable and non-communicable, are major causes of ill health.
  • other factors including diet, stress and life situations may have a profound effect on mental and/or physical health. 
  • different types of diseases may and often do interact.
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B5.2: Pathogens and Disease

  • communicable diseases are caused by micro-organisms called pathogens, which include bacteria, viruses, fungi and protists. 
  • bacteria and viruses reproduce rapidly inside your body. 
  • bacteria can produce toxins that make you feel ill.
  • viruses live and reproduce inside your cells, causing cell damage. 
  • pathogens can be spread by direct contact, by air or by water.
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B5.3: Preventing Infections

  • the spread of disease can be prevented by simple hygeine measures, by destroying vectors, by isolating infected individuals and by vaccination. 
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B5.4: Viral Diseases

  • measles virus is spread by droplet infection. it causes fever and a rash and can be fatal. there is no cure. isolating patients and vaccination prevents its spread. 
  • HIV initially causes flu-like illness. unless it is successfully ontrolled by antiretroviral drugs the virus attacks the body's immune cells.
  • late stage HIV is called AIDS and occurs when the immune system is so badly damaged, it cannot fight off or deal with infections or cancers.
  • HIV is spread by sexual contact, exchange of bodily fluids or when drug users share needles. 
  • tobacco mosaic virus is spread by contact and vectors. it damages the leaves and reduces photosynthesis. there is no treatment for TMV. spread is prevented and contained by field hygiene and pest control. 
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B5.5: Bacterial Infections

  • salmonella is spread through undercooked food and poor hygiene. toxins in the bacteria cause vomiting, diarrhoea and cramps. poultry in the UK are vaccinated against salmonella to control its spread.
  • gonorrhoea is a sexually transmitted disease. pain when urinating or discharge from the genitals are the symptoms. treatment includes antibiotics, however some strains of the disease are resistant. 
  • there are few bacterial plant infections 
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B5.6: Diseases Caused by Fungi and Protists

  • rose black spot is a fungal disease spread in the environment by wind and water. it damages leaves so they drop off, reducing photosynthesis. spread is controlled by removing the affected leaves and using chemical sprays but this isn't very effective.
  • malaria is caused by parasitic protists and is spread by the bite of a female mosquito. it damages blood and liver cells and can be fatal. some drugs are effective but protists are becoming resistant. using a mosquito net prevents being bitten and infected and preventing the vectors breeding stops their spread. 
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B5.7: Human Defence Responses

  • bodies have several 'lines of defence' against pathogens, including the skin, the nose, the trachea, the bronchi and the stomach. 
  • white blood cells help defend against pathogens by ingesting them and making antibodies and antitoxins. 
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