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
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:
A virus can only survive outside a host for a very short time, however they are responsible for many diseases;
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:
Protozoa are single-celled organisms which are typically mobile. They can cause:
Malarial infestation by Plasmodium
Multicellular parasites include tapeworms and hookworms (pictured).
They can cause
Short clip of tapeworms in situ
These pathogens can be transmitted in many ways:
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.
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.
Knowing what we do about transmission of pathogens there are a number of things that can be used to prevent it;
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.
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 is the study of the characteristics of an infectious disease.
We would look at:
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
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