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Infection and immunity
Infection and immunity

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In this free course on Infection and immunity you have learned that from prion to protists, via all manner of pathogenic bacteria, viruses and parasites, it is clear that pathogens pose a major threat to human health. Through our immune systems we possess some effective weapons to fight off them off, but these aren’t fool proof; infectious diseases remain a major health care challenge.

However, with the careful use of the scientific method we can understand more about the nature of pathogens and use this information to develop new strategies to prevent – and perhaps eradicate – the deadly threat they pose.

  • Infectious diseases kill around 10 million people every year worldwide and are caused by pathogens.
  • There are more than 1400 different pathogens that cause human diseases, but only about 20 cause two-thirds of human deaths from infection.
  • There are many types of pathogen, including multicellular parasites, single-celled protists, yeasts and bacteria, as well as viruses and prions.
  • Pathogens can be transmitted directly or indirectly. Direct methods included transmission by touch, sexual transmission and mother-to-child transmission. Indirect methods involve transmission via air, water or food, such as the faecal–oral route and environmental contamination.
  • The underlying causes of infectious diseases include biological susceptibility, the social and economic conditions in which people live, and behaviours that influence the spread of infection.
  • The symptoms of a disease can only be experienced by the person who suffers from them, whereas the signs of a disease can be observed by others.
  • Infectious diseases may be acute, resulting in recovery or death within a few weeks, or chronic and slowly progressing over months or years; a chronic condition may include an acute episode.
  • The application of the scientific method has been central in humankind’s fight against infectious disease, and is characterised by systematic observation, measurement, experiment, and the formulation, testing and modification of hypotheses.
  • Early examples of the use of the scientific method include John Snow’s experiment of removing the handle from the Broad Street pump, which demonstrated that cholera was transmitted in contaminated water almost 30 years before bacteria were identified, and Edward Jenner’s smallpox inoculation experiment.
  • A person’s defences against pathogens begin with physical and chemical barriers such as intact skin; when these are breached we rely on our immune system to fight infection.
  • The immune system has two distinct branches – innate and adaptive immunity – each of which uses different types of leukocytes.
  • The innate immune system is non-specific; the leukocytes involved cannot distinguish between different types of pathogen. By contrast, leukocytes involved in adaptive immunity are specific to different pathogens.
  • Some adaptive immune system leukocytes have a ‘memory’. This leads to more effective immune responses with each exposure to the pathogen.

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If you enjoyed the course and are thinking about studying the module this material was adapted from (SDK100 Science and health, an evidence based approach) you can read more about the module and the health sciences qualification. You can also undertake a self-diagnostic quiz to check whether you have the necessary background knowledge and skills to cope with studying SDK100.