Summary
Infectious diseases are caused by microorganisms (bacteria, fungi, protozoa) or viruses that get into the body. They spread through the air when people cough, by contact, through contaminated water or food, or via animals such as mosquitoes. Other diseases, such as type 2 diabetes or heart disease, are not infectious: they are not catching and depend on genes and lifestyle.
The body defends itself in several lines. Skin and mucous membranes keep germs out; if they get through, white blood cells attack them: some eat them and others make antibodies that recognise each germ and leave a memory. Vaccines use that memory to prepare us before infection, and antibiotics kill bacteria but are useless against viruses.
Key points
- Infectious diseases are caused by bacteria, viruses, fungi or protozoa.
- A virus is not a cell: it can only multiply inside other cells.
- Skin and mucous membranes are the first barrier.
- White blood cells attack germs; lymphocytes make antibodies.
- Vaccines teach the body to recognise a germ and leave a memory.
- Antibiotics work against bacteria, not viruses.
- Misusing them creates resistant bacteria.
- Non-infectious diseases depend on genes and lifestyle.