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Transmission and control of infectious diseases. Learning intentions Describe the different types of pathogens which can cause a disease Describe how infectious diseases can be transmitted from person to person. Describe good practices to control or reduce the spread of the disease

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Learning intentions

  • Describe the different types of pathogens which can cause a disease
  • Describe how infectious diseases can be transmitted from person to person.
  • Describe good practices to control or reduce the spread of the disease
  • Describe the term epidemiology
  • Describe the terms sporadic, endemic, epidemic and pandemic
  • Describe the control measures which can be used in the event of an epidemic
what are pathogens
What are pathogens?

As we have seen, pathogens are agents which can cause disease.

They can include many different types of organisms including:


Bacteria are single-celled organisms and can cause diseases such as:

  • Cholera
  • Typhoid
  • Salmonella
  • Pneumonia
  • Tuberculosis

A virus can only survive outside a host for a very short time, however they are responsible for many diseases;

  • AIDS
  • Chicken pox
  • Influenza
  • Herpes

And some cases of cancer, e.g. Cervical cancer caused by the Human papillomavirus (HPV)


Fungi are widely used by humans but some can cause diseases like:

  • Thrush
  • Ringworm
  • Athlete’s Foot

Protozoa are single-celled organisms which are typically mobile. They can cause:

  • Malaria
  • Sleeping sickness
  • Dysentery

Malarial infestation by Plasmodium

multicellular parasites
Multicellular parasites

Multicellular parasites include tapeworms and hookworms (pictured).

They can cause

  • Anaemia
  • Diarrhoea
  • Low birth weight

Short clip of tapeworms in situ

pathogen transmission
Pathogen Transmission

These pathogens can be transmitted in many ways:

  • Direct physical contact
  • Inhaled air
  • Indirect physical contact
pathogen transmission1
Pathogen transmission
  • Exchanging body fluids
  • Faecal-oral route
  • Vector organisms
controlling transmission
Controlling transmission

Because we know how pathogens are transmitted we can interrupt it by the following;

- Antisepsis – inhibiting or destroying a microorganism by sterilising everything that could carry a pathogen or prevent them reaching somewhere.

controlling transmission1
Controlling transmission

Quarantine – isolating the person who is infected or has been in contact with an infected person to prevent spreading of the disease.

The length of the

quarantine is usually just over the length of time it usually takes for someone to display symptoms after being infected.

individual responsibility
Individual responsibility

Knowing what we do about transmission of pathogens there are a number of things that can be used to prevent it;

  • Good hygiene – washing hands, brushing teeth, showering
  • Care in sexual health – use of condoms to prevent sexually transmitted diseases
  • Handling and storage of food – washing hands, keeping raw and cooked food separate and at the appropriate temperatures.
community responsibility
Community responsibility

Clean water supply – our water is filtered and chlorinated to prevent growth of microorganisms… is everyone as lucky?

Safe food webs – for example, milk pasteurisation (heating at 72o C to kill any microorganisms)

Waste disposal – keeping any refuse collected regularly and buried or incinerated.

community responsibility1
Community responsibility

Control of vectors – Taking care to eradicate any animals which can carry diseases e.g.

Bubonic plague was caused by bacteria carried by fleas on rats so being in close proximity to rats carrying those fleas put you at high risk.

Malaria is caused by a protozoa carried by female mosquitoes in their saliva. How could you protect people from this animal vector?

epidemiology of infectious diseases
Epidemiology of infectious diseases

Epidemiology is the study of the characteristics of an infectious disease.

We would look at:

  • The location of an initial outbreak
  • The pattern and speed of the spread
  • The geographical distribution
patterns of distribution
Patterns of distribution

Sporadic – occurs in scattered or isolated instances with no connection between them

Endemic – recurs as a regular number of cases in a particular area

Epidemic – affects an unusually high number of people in a particular area

Pandemic – occurs as a series of epidemics spreading across continents or the whole world

what can we hope to do with this
What can we hope to do with this?

It is essential to understand how diseases spread so that we are able to identify appropriate control measures should an outbreak occur.

Think of the Swine ‘flu outbreak -

For overview of methods used to stop the spread of infection see the following clip