Communicable Diseases (4.3.1)

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  • Communicable Diseases (4.3.1)
    • Communicable (Infectious) Diseases (
      • Pathogens are microorganisms that cause infectious disease.
      • Pathogens may be viruses, bacteria, protists or fungi that ca infect plants or animals.
      • Bacteria can produce poisons (toxins) that damage tissues and make us feel ill.
      • Viruses live and reproduce inside body cells, which causes damage to the cell,
      • Explain how :Pathogens can be spread by direct contact, by water or air.
      • Explain how the spread of disease can be reduced or prevented.
    • Viral Diseases (
      • Measles is a viral disease showing symptoms of fever and a red skin rash and that it is a serious illness that can be fatal if complications arise (which is why most young children are vaccinated against measles).
      • Describe how: the measles virus is spread by air (by inhalation of droplets from sneezes and coughs).
      • HIV infection initially causes flu-like illness and the virus attacks the body's immune cells (white blood cells) if it is not successfully controlled with antiretroviral drugs.
      • AIDS occurs when the body's immune system becomes so badly damaged it can no longer deal with other infections or cancers.
      • Explain how HIV is spread (by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles)
      • TMV is a widespread plant pathogen affecting many species os plants including tomatoes and that it gives a distinctive 'mosaic' pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis.
    • Bacterial Diseases (
      • Salmonella food poisoning ia caused by bacteria that are spread by ingesting contaminated food.
      • Describe the symptoms of Salmonella food poisoning as : fever, abdominal cramps, vomiting and diarrhoea which are caused by the bacteria and the toxins they secrete.
      • In the UK, poultry are vaccinated against Salmonella to control the spread
      • Gonorrhoea is a sexually transmitted disease that is caused by bacteria.
      • Describe the symptoms of Gonorrhoea as: a thick yellow or green discharge from the vagina or penis and pain when urinating
      • Gonorrhoea was easily treated with penicillin until many resistant strains of the bacteria appeared.
    • Fungal Diseases (
      • Rose Black Spot is a fungal disease where purple or black spots develop on leaves, which often turn yellow and drop early
      • Rose black spot fungus affects the growth of the plant because photosynthesis is reduced.
      • Describe how: Rose Black Spot fungus is spread by water and air.
      • Explain how: Rose Black Spot fungus can be treated by using fungicides and/or removing and destroying the affected leaves.
    • Protist Diseases (
      • Pathogens that cause malaria are protists.
      • Malaria causes recurrent episodes of fever and can be fatal.
      • Describe the life cycle of the malarial protist, including the role of the mosquito.
      • Explain how: the spread of malaria can be controlled by preventing mosquitos (the vector) from breeding and by using nets to avoid bites.
    • Human Defence Systems (
      • Describe how: the non-specific defence systems of the human body (including skin, nose, trachea and bronchi and stomach) protect against pathogens.
      • Explain how: white blood cells use phagocytosis to defend against pathogens.
      • Explain how: white blood cells produce antibodies to defend against pathogens
      • Explain how white blood cells produce antitoxins to defend against pathogens.
    • Vaccination (
      • A vaccine contains small quantities of dead or inactive forms of a pathogen.
      • Explain how: having a vaccination stimulates the white blood cells to produce antibodies against a particular pathogen and that if the same pathogen then enters the body, the white blood cells are able to respond quickly to produce the correct antibodies, preventing infection.
      • Explainhow: the spread of pathogens can be reduced by immunising a large proportion of the population.
    • Antibiotics and Painkillers (
      • Antibiotics such as penicillin, are medicines that help to cure bacterial disease by killing bacteria inside the body.
      • It is important that specific bacteria should be treated by specific antibodies
      • Antibiotics cannot kill viral pathogens and that it is difficult to develop drugs that kill viruses without also damaging the body's tissue.
      • Describe how: the use of antibiotics has greatly reduced deaths from infectious bacterial diseases, but the emergence of strains of bacteria that are resistant to antibiotics is of great concern.
      • Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens
    • Discovery and Development of Drugs (
      • Describe how: traditionally drugs were extracted from plants and microorganisms for example:
      • Describe how: most new drugs are synthesised by chemists in the pharmaceutical industry, but that the starting point may still be a chemical extracted from a plant
      • New drugs have to be extensively tested for toxicity, efficacy, and dose
      • Describe how: preclinical testing is done in a laboratory using cells, tissues and live animals.
      • Describe how: clinical trials use healthy volunteers and patients and that very low doses of the drug are given at the start of a clinical trial
      • If the drug is found to be safe after initial trials, further clinical trials are carried out to find the optimum dose for the drug.
      • In double blind trials, some patients are given a placebo.


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