|Example in animals||Example in plants|
|Viruses||HIV/AIDS||Tobacco mosaic virus|
|Fungi||Athlete's foot||Black rose spot|
All types of pathogen have a simple life cycle. They infect a host, reproduce themselves or replicate if it is a virus, spread from their host and infect other organisms. They also all have structural adaptations that make them successful at completing their life cycles, which enable them to cause more disease.
Diseases caused by pathogens are called communicable diseases. This means the disease can be transferred from an infected organism to another organism.
There are other types of disease which cannot be passed from organism to organism. These are called non-communicable diseases:
Transmission can occur in a number of important ways, as shown in the table below.
|Type of transmission||Example|
|Direct contact||This can be sexual contact during intercourse or non-sexual contact, like shaking hands.|
|Water||Dirty water can transmit many diseases, such as the cholera bacterium.|
|Air||When a person who is infected by the common cold sneezes, they can spray thousands of tiny droplets containing virus particles to infect others.|
|Unhygienic food preparation||Undercooked or reheated food can cause bacterial diseases like Escherichia coli which is a cause of food poisoning.|
|Vector||Any organism that can spread a disease is called a vector. Many farmers think tuberculosis in their cattle can be spread by badgers.|