1. Transmission and control of infectious diseases

2. 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

3. What are pathogens?
As we have seen, pathogens are agents which can cause disease. They can include many different types of organisms including:

4. Bacteria
Bacteria are single-celled organisms and can cause diseases such as:
Cholera
Typhoid
Salmonella
Pneumonia
Tuberculosis

5. Viruses
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)

6. Fungus
Fungi are widely used by humans but some can cause diseases like:
Thrush
Ringworm
Athlete’s Foot

7. Protozoa
Protozoa are single-celled organisms which are typically mobile. They can cause:
Malaria
Sleeping sickness
Dysentery
Malarial infestation by Plasmodium

8. Multicellular parasites
Multicellular parasites include tapeworms and hookworms (pictured).
They can cause
Anaemia
Diarrhoea
Low birth weight
Short clip of tapeworms in situ

9. Pathogen Transmission
These pathogens can be transmitted in many ways:
Direct physical contact
Inhaled air
Indirect physical contact

10. Pathogen transmission
Exchanging body fluids
Faecal-oral route
Vector organisms

11. 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.

12. 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.

13. 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.

14. 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.

15. 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?

16. 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

17. 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

18. 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