Pathogens are microoganisms that causes infectious disease. Some bacteria and viruses are pathogens. These bacteria and viruses reproduce inside the body producing poisons (toxins) that make us feel ill. Howevere, pathogens reproduce before they make enough toxins to make you feel ill.
Semmelweiss discovered that infections could be transferred between patients in a hospital. He siad that washing your hands between treating patients helped you stop transfer infection. However, it was mainy years before doctors took his ideas seriously.
White blood cells do three things to help us protect ourselves:
- They can ingest pathogens, meaning they digest and destroy the pathogens.
- They produce antibodies to help destroy a particular pathogen.
- They produce antitoxins to counteract (neutralise) the toxins that the pathogens produce.
It is best to have no pathogens in your body by having no cuts on your skin and trapping pathogens in the mucus in your nose. If pathogens do get in then white blood cells help us to defend ourselves.
When you sneeze millions of droplets carrying pathogens fly out of your mouth and nose at about 100 miles and hour.
Using Drugs to Treat Disease
- Antibiotics kill infective bacteria in the body, penicillin is a well known antibiotic.
- Viruses are much more difficult to kill, as they live inside our cells. As they reproduce inside the cell when trying to kill them you may kill the cell as well.
- Painkillers may make you feel better, but do nothing to kill the disease causing the pain.
The MRSA 'superbug' is a bacterium that has evolved in hospitals though natural selection. It is resisant to commonly used antiboitics.
Some pathogens, particularly viruses, can mutate resulting in new forms.
Very few people are immune to these new pathogens and so disease can spread quickly within a country (epidemic) or across countries (pandemic.) These are very difficult to control.
REMEMBER: Mutation happens instantly and natural selection takes many years.
Developing New Medicines
It cost a lot of money to develop a new medicine. It also takes a long time as new medicines must be tested to see if they are toxic and to see if they are effective in curing the disease. This work is carried out in labortories on animals and humans who volunteer.
If these tests are not thorough enough then a new medicine may have dangerous side effects. Thalidomide is a medicine that was widely used in the 1950s as a sleeping pill, and it also helped to prevent 'morning sickness' in pregnent women. It wasn't tested properly and women started giving birth to with babies with severe limb abnormalities. It is now not used with pregnent women but used to cure leprosy.
- Dead or inactivie forms of an organism can be made into a vaccine, and these are injected into the body.
- The white blood cells react by producing antibodies, this makes the person immune and prevents further infection because of the body ever saw a real version of that pathogen it would responds quickly by producing more antibodies.
- There is an argument over whether some vaccines are completely safe, eg the MMR (measles, mumbs and rubella) vaccine.