Pathogens

Infectious diseases are caused by tiny living things. There are two types, bacteria and viruses.

They get inside our bodies (e.g. through a cut, in our food, in the air we breathe, when we have sex) then multiply rapidly.

Bacteria
These are made up of just one cell. They can live anywhere. Most bacteria are completely harmless (some are very useful) but some are designed to invade our bodies. The chemicals they produce can make us ill.

Cholera	Tetanus	Salmonella	Leprosy

Viruses
Viruses can only reproduce inside a host cell. They are very small.

Smallpox	Flu	AIDS	Rabies

REMEMBER

Micro-organisms that cause infectious disease are called 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.