Communicable Disease

• There are several types of pathogen
• Pathogens are microorganisms that enter the body and cause disease
• Pathogens cause communicable diseases - diseases that can easily spread
• Both plants and animals can be infected by pathogens
• Bacteria are very small living cells
• Bacteria are about 1/100th the size of your body cells which can reproduce rapidly inside your body
• Bacteria can make you feel ill by producing toxins that damage your cells and tissues
• Viruses are not cells - they're much smaller
• Viruses are not cells. They're about 1/100th the size of a bacterium
• Like bacteria, viruses can reproduce rapidly inside your body
• Viruses live inside your cells and replicate themselves using the cells' machinery to produce many copies of themselves. The cell will usually then burst, releasing all the new viruses. This cell damage is what makes you feel ill
• Protists are single-celled eukaryotes
• There are lots of different types of protists. But they're all eukaryotes and most of them are single-celled
• Some protists are parasites. Parasites live on or inside other organisms and can cause them damage. They are often transferred to the organism by a vector, which doesn't get the disease itself - e.g. an insect that carries the protist
• Some fungi are single-celled. Others have a body which is made up of hyphae (thread-like structures). These can grow and penetrate human skin and the surface of plants, causing diseases
• Hyphae can produce spores, which can be spread to other plants and animals
• Pathogens can be spread in different ways
• Water - some pathogens can be picked up by drinking or bathing in dirty water. E.g. cholera is a bacterial infection that's spread by drinking water contaminated with the diarrhoea of other sufferers
• Air - pathogens can be carried in the air and can then be breathed in. Some airborne pathogens are carried in droplets produced when you cough or sneeze - e.g. the influenza virus that causes flu is spread this way
• Direct contact - some pathogens can be picked up by touching contaminated surfaces, including the skin. E.g. athlete's foot is a fungus which makes skin itch and flake off. It's most commonly spread by touching the same things as an infected person, e.g. shower floors and towels