Miasma Theory and Edwin Chadwick

Miasma Theory- There have been many ideas on how diseases are spread. The miasma theory has been around for 1000s of years. The theory suggest that diseases are spread by bad smells/ noxious air. It was very prevalent throughout the middle ages and lasted until the late nineteenth century. Miasma Theory is a good example of correlation.  

Public health

Spec point: There is also a strong correlation between poverty and the occurrence of infectious disease

In 1842, Edwin Chadwick saw this link and argued preventing disease would reduce the poor rates.

Edwin Chadwick and others helped put in place public health policies. For example, many towns and cities built public sewage systems. After the implementation of these new public hygiene measures, outbreaks of cholera, typhoid, dysentery were greatly reduced. This provide more evidence for miasma theory. This is an example of post hoc ergo propter hoc. 

'Post hoc ergo propter hoc' means after this therefore because of this.

Based upon the mistaken notion that simply because one thing happens after another, the first event was a cause of the second event.  

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Germ Theory and types of pathogens

Correlation between variables may indicate a link, but this could be just a coincidence. To see if one causes the other, experiments need to be performed to show a direct connection.

Spec Point: Communicable diseases could included HIV/AIDS, malaria, cholera, tuberculosis, influenza and Ebola.

 Germ Theory

  • First proposed by Italian polymath, Girolamo Fracastro in 1546 (in absence of knowledge of microorganisms), but there was very little evidence to support this theory at the time.
  • Infectious diseases are caused by pathogens (bacteria, protest, virus, prion and worms)

 Prion-  an abnormal form of a normally harmless protein found in the brain that is responsible a variety of fatal neurodegenerative diseases

Virus-  a small infectious agent that can only replicate inside cells of another organisms.

Bacteria- a member of a large group of unicellular microorganisms which have cell walls but lack organelles and an organized nucleus, including some which can cause disease.

Protists- A protist is any eukaryotic organism that is not an animal, plant or fungus.

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John Snow and Epidemiologists

Spec point: Causal relationships have been established between some pathogens and infectious diseases

Spec Point: Epidemiologists study the incidence, distribution and control of diseases/ disorders

1854: John Snow - mapping cholera outbreak to a communal water pump in London 

Back in 1854, John snow was successful in identifying sufferers of cholera in a small region in London. In today's modern times, outbreaks of diseases can spread over large areas/ countries/ continents very fast

How could epidemiologists use modern technology to track and predict the spread of diseases such as bird flu?

  • Improved reporting links
  • Improve reporting from medical practitioners
  • Improved diagnostic technology
  • Models of people movements
  • Social media

Spec point: Progress in diagnosis and treatment of many diseases and disorders has been advanced by scientific research

Spec Point: Vaccinations can prevent and eliminate some diseases. In some countries, public understanding has been influenced by non-scientific opinions

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White Blood Cells

There are several types of white blood cells. Their main role is to protect the body against invasion by disease-causing microorganisms (pathogens), such as bacteria and viruses. They do this in two main ways: phagocytosis and antibody production.

About 70% of white blood cells can ingest (take in) microorganisms such as bacteria. This is called phagocytosis, and the cells are phagocytes. They do this by changing their shape, producing extensions of their cytoplasm, called pseudopodia. The pseudopodia surround and enclose the microorganism in a vacuole. Once it is inside, the phagocyte secretes enzymes into the vacuole to break the microorganism down. Phagocytosis means 'cell eating'- you can see why it is called this.

Approximately 25% of white blood cells are lymphocytes. Their function is to make chemicals called antibodies. Antibodies are soluble proteins that pass into the plasma. Pathogens such as bacteria and viruses have tell-tale chemical 'markers' on their surfaces, which the antibodies recognise. These markers are called antigens. The antibodies stick to the surface antigens and destroy the pathogen. They do this in a number of ways, for example by:

  • Causing bacteria to stick together, so that phagocytes can ingest them more easily.
  • Acting as a 'label' on the pathogen, so that it is more easily recognised by a phagocyte
  • Causing bacterial cells to burst open
  • Neutralising poisons (toxins) produced by pathogens.
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White Blood Cells

 Some lymphocytes do not get involved in killing microorganisms straight away. Instead, they develop into memory cells. Memory cells make us immune to a disease. These cells remain in the blood for many years, sometimes a lifetime. If the same microorganism re-infects, the memory lymphocytes start to reproduce and produce antibodies, so that the pathogen can be quickly dealt with.

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Vaccination involves introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies. If the same pathogen re-enters the body the white blood cells respond quickly to produce the correct antibodies, preventing infection.

Vaccination will prevent illness in an individual. The spread of pathogens can be reduced by immunising a large proportion of the population.

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Reasons people might not get vaccinated

For what reasons might people not get vaccinated?

  • Availability
  • Geographical isolation
  • Refrigeration of vaccines in hot climates
  • Security of medical personnel
  • Cost
  • Perception of Safety (e.g. MMR vaccination)
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MMR- A case study

1998 publication in the Lancet by Andrew Wakefield that autism was linked to the combined vaccination for mumps, measles and rubella (MMR)

This was picked up by the media, and people stopped vaccinating their children. As a result, there has been significant rises in measles and mumps resulting in deaths and permeant injuries.

Subsequent investigation, showed that Andrew Wakefield had, undeclared conflicts of interest (possible showing unbiased opinions) and had manipulated evidence. Epidemiological studies have revealed.

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Faulty Reasoning

Scientists have to be constantly on the lookout for these biases.

These biases include:

  • Confirmation Bias- is a type of cognitive bias that involves favouring information that confirms your previously existing beliefs or biases.
  • Hasty generalisations
  • Post hoc ergo propter hoc (false cause)
  • Straw man fallacy- the distortion of a strong piece of evidence that artificially weakens a hypothesis.
  • Redefinition (moving the goal posts)
  • Appeal to tradition
  • False authority
  • Accumulation of anecdotes being regarded as evidence
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Faulty Reasoning

Spec Point: Some health practices are not evidence based.

Pseudoscience is the term applied to those beliefs and practices which claim to be scientific but do not meet or follow the standards of proper scientific methodologies

Some medical practices that could be considered as pseudoscience's are:

  • Reflexology
  • Homeopathy
  • Magnetism
  • Colonic hydrotherapy
  • Acupuncture
  • Chiropractic treatments. 
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Placebo Effect

The apparent improvement in a patient's health after the patient has perceived to have been treated.

The placebo effect can be quite powerful. Examples include:

  • Patients being told they have been given an anaesthetic and undergoing operations
  • Placebo effects seen on our pets
  • Non-alcoholic beer still can make students drunk
  • Even when patients are later told they have been given a fake drug (called a placebo), they still improve.

 Spec Point: New diseases are appearing due to pathogens crossing species barriers

Spec.Point: Increased life expectancy in some countries will have negative consequences on resources and medical care.

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Arachidonic acid is a natural molecule that induces inflammation. It binds to an active site in a protein called COX-1. Aspirin binds with COX-1 and prevents arachidonic acid getting to the active site.

The effectiveness of a drug is closely related to the chemical groups present and the three-dimensional shape of the molecule.

To understand the shape of proteins, you need to know how they are made:

  1. Proteins are made up of subunits called amino acids. There are 20 types of amino acids
  2. The amino acids are assembled in a specific sequence depending on the DNA code in chromosomes
  3. Depending on the exact sequence of amino acids, the protein will fold into a specific shape.
  4. Generally, there are two subtypes of shapes within a protein: helixes on sheets. 
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Computer software is used to predict the shape of proteins and help design interacting molecules as potential drugs.

Experimentation and clinical studies are needed to demonstrate the effectiveness, safety, and limitations of new drugs.

 What is informed consent?

  • The agreement to participate in a drug trial after being are fully informed of the purposes, potential benefits/risks of the trial

 What is meant by a double blind trial?

  • A better experimental design is when both the research subjects and clinicians are unaware of which treatment is which.

 In a recent Ebola Outbreak in Africa, an untested vaccine was used to treat patients. What are the ethical issues of using experimental drugs on patients?

  • Consent needed
  • Drug may cause more harm
  • Drugs availability should not be based on social/financial/national standing
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Problems of using experimental Drugs

Outline the problems if using experimental drugs on infected people:

  • Unknown risks/benefits
  • Legal implications
  • Limited supplies
  • Expensive
  • No approval license
  • Should only be used if no other treatment is available.
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