Defence against disease Microorganisms that cause infectious disease

Defence against disease

Microorganisms that cause infectious disease are called pathogens. Which Pathogens can you name?

These are “Rod – shaped” Bacteria on the end of a pin.

Viruses are much smaller than bacteria. They invade body cells and then hijack the cells DNA to reproduce. They can cause lots of damage to cells.

Bacteria, Viruses and Fungi are all Pathogens. Bacteria and viruses may reproduce rapidly inside the body and may produce poisons (toxins) which make us feel ill. Viruses damage cells in which they reproduce.

• The body has different ways of protecting itself against pathogens. White blood cells help to defend against pathogens: − by ingesting pathogens − by producing antibodies which destroy particular bacteria or viruses − by producing antitoxins which counteract the toxins (poisons) released

Ingesting Pathogens White Blood Cell approaches pathogen Pathogen White Blood Cell stretches to form a bubble around the pathogen. White Blood Cell releases enzymes to digest the pathogen. The process is complete.

Producing Antibodies

Producing Antitoxins Bacteria The bacteria produces toxins White Blood Cell The White Blood Cell produces antitoxins to neutralise the toxins.

Other causes of Disease • Genetic causes – inherited from parents • Parasitic - you can catch an organism that causes a disease – e. g. malaria – protozoa, thread worm crab lice

Immunisation People can be immunised against a disease by introducing small quantities of dead or inactive forms of the pathogen into the body (vaccination). Vaccines stimulate the white blood cells to produce antibodies that destroy the pathogens. This makes the person immune to future infections by the microorganism, because the body can respond by rapidly making the correct antibody, in the same way as if the person had previously had the disease. An example is the MMR vaccine used to protect children against measles, mumps and rubella.

The first vaccine was against a virus called small pox. Small pox is a dreadful disease that killed hundreds of thousands of people especially children. Those it did not kill were usually horribly scarred. In the nineteenth century Edward Jenner noticed that cow maids often caught cow pox, a less dangerous form of small pox. If the cow maids ever caught small pox they recovered quickly and with not many complications. Jenner came up with a theory that if someone was deliberately infected with cow pox then they would be immune to small pox.

What Jenner did next has caused much debate in science. Jenner took a sample of cow pox from a milk maid and using a needle put it into his son. His son duly caught cow pox and recovered. That may sound a bit cruel but what Jenner did next was worse he took a sample of the deadly small pox and using the same method injected that into his son as well. Jenner was lucky his son lived and proved his theory correct.