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-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?

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

They can include many different types of organisms including:

BacteriaBacteria are single-celled

organisms and can cause diseases such as:

- Cholera- Typhoid- Salmonella- Pneumonia- Tuberculosis

VirusesA virus can only survive outside

a host for a very short time, however they are responsible for many diseases;

- AIDS- Chicken pox- Influenza- HerpesAnd some cases of cancer, e.g.

Cervical cancer caused by the Human papillomavirus (HPV)

Fungus

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

- Thrush- Ringworm- Athlete’s Foot

Protozoa

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

- Malaria- Sleeping sickness- Dysentery

Malarial infestation by Plasmodiumhttp://www.youtube.com/watch?v=OEDhe4MPEMc

Multicellular parasites

Multicellular parasites include tapeworms and hookworms (pictured).

They can cause- Anaemia- Diarrhoea- Low birth weight

Short clip of tapeworms in situhttp://www.youtube.com/watch?v=JeDD0HdecGk

Pathogen Transmission

These pathogens can be transmitted in many ways:

- Direct physical contact

- Inhaled air

- Indirect physical contact

Pathogen transmission

- Exchanging body fluids

- Faecal-oral route

- Vector organisms

Controlling transmissionBecause 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 transmissionQuarantine – 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 responsibilityKnowing 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 responsibilityClean 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 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 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

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?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 - http://www.bbc.co.uk/news/10483218

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

https://www.youtube.com/watch?v=lEzTBzh4NQg