Pathogens

Basic Information

Pathogens tend to be microorganisms which cause infectious diseases with symptoms. The three main types of pathogen are:
- bacteria
- fungi
-viruses
Bacteria and viruses reproduce rapidly and may produce poisons or toxins. Viruses damage the body cells that they reproduce in. All viruses are pathogens but not all bacteria and fungi are.

Ways that Pathogens Spread

Pathogens can spread in a number of ways, including:

- airborne
- mouldy food
- dirty water
- dirty needles
- blood transfusions
- animal bites
- touching infected materials
- openings (e.g. cuts)
- sneezing
- placenta
- breast milk

Defending Against Pathogens

Body Defenses

- ear wax traps bacteria
- tears contain antibacterial substances
- skin acts as a barrier (tough and waterproof)
- stomach acid (hydrochloric acid)
- cilia wafts mucus away from lungs
- sweat
- platelets clot blood to make a scab
- white blood cells make antibodies

White blood cells are very important in defending the body against infection. They can destroy pathogens in three ways:
- ingesting the pathogen
- producing antibodies to fit the pathogen's antigen
- producing antibodies to neutralise toxins

Once a white blood cell has met a pathogen once memory cells remember the antibodies needed to defeat it, so if the pathogen enters your body again it will rapidly produce the antibody to stop you being ill. This is called immunity.
However, this only works on bacterial infections. This is because viruses can mutate their antigen (the outer shell of the virus) so the memory cells don't recognise it and have to go through the process again.

Vaccinations

Drugs for killing viruses are difficult to develop because the virus reproduces inside cells and drugs can damage or destroy body cells as well as the virus. As well as this. However, vaccinations for bacterial infections are highly effective. Vaccinations are an injection of a dead, inactive or weakened form of the pathogen or toxin. This triggers the natural immune response to create antibodies to destroy the pathogens. If the pathogen re-enters the body the memory cells remember it and rapidly produce antibodies so you don't become ill.

In 1998 Dr. Wakefield published a study linking the mumps, measles and rubella (MMR) vaccine to autism development in children. This hugely decreased public confidence in the vaccination, even after the study was proved to be false.

Drugs

Developing drugs takes a very long time because they go through a rigorous process to determine if they are safe:

- disease is chosen and ideas for treatment brainstormed
- search for the correct drug, either by a computer design software or screening chemicals
- drug is made (synthesised)
- tested on live cells, tissues or organs to see if it is toxic
- animal testing for damage or side effects
- animal testing continues to check for long term problems as - human trials begin testing on healthy volunteers
- patient trials begin to see if it is safe and effective and to check dosage
- patient trials continue with a larger group

- when medicine has past all the tests it is approved and licensed to be prescribed
- continued monitoring

At any point that a drug fails the tests it must be pulled and a new drug found. However, sometimes even this rigorous testing fails to identify dangerous drugs. In the 1950s a new drug was developed named Thalidomide for use as a sleeping pill. It was then discovered that it could also be effectively prescribed to treat morning sickness, however it was later discovered that the drug caused limb abnormalities in the foetus. As a result, there were a large number of babies born in the 1950s with these abnormalities. In 1968 a new law set standards higher for drug testing.

A painkiller reduces the symptoms of infections and antibiotics are used to treat bacterial infections.

Drugs need to be:

- effective
- safe
- stable (don't break down in body)
- excretable (as waste once they have been effective)

Reducing Spread of Infection

There are a number of ways to reduce the likelihood of contracting the infection in the first place:

- washing hands (with soap)
- disinfectant
- plastic gloves
- correctly preparing food
- chlorine in pools
- sneezing into a tissue
- isolation (quarantine)
- sanitizer
- clean drinking water
- dressing a wound

	Created by Kit Sinclair almost 10 years ago

GCSE Sciences (Biology) Note on Pathogens, created by Kit Sinclair on 19/04/2015.