Pathogens are disease-causing viruses, bacteria, fungi or protists, which can infect animals and plants. Humans have an immune system, which can defend them from pathogens.
Greg James describes the effects of bacterial growth, and how to prevent foodborne illness
A pathogen is a microorganism that causes a disease. There are four main types of pathogen:
| Pathogen | Example in animals | Example in plants |
|---|---|---|
| Viruses | HIV potentially leading to AIDS | Tobacco mosaic virus |
| Bacteria | Salmonella | Agrobacterium |
| Fungi | Athlete's foot | Black rose spot |
| Protists | Malaria | Few known |
Transmission can occur in a number of important ways, as shown in the table below:
| Type | Examples |
|---|---|
| Direct contact | Contact such as shaking hands or touching contaminated surfaces. |
| Water | Dirty water can transmit many diseases, such as the cholera bacterium. |
| Aerosol (airborne) | When a person who is infected by the common cold sneezes, they can spray thousands of tiny droplets containing virus particles into the air that others breathe in. |
| 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. |
| Contaminated food | Undercooked or reheated food can cause bacterial diseases like Escherichia coli (e coli) which is a cause of food poisoning. |
| Vector (insects) | Any organism that can spread a disease is called a vector. Some farmers think tuberculosis in their cattle can be spread by badgers. |
| Body fluids | These can be exchanged during sexual intercourse. |