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A pathogen is a microorganism that causes disease. This lesson covers the different types of pathogens, how diseases are transmitted, and the mechanisms by which pathogens cause disease. These are essential topics for the Edexcel A-Level Biology (9BI0) specification.
A pathogen is an organism or agent that causes disease in its host. Pathogens include:
| Type | Examples |
|---|---|
| Bacteria | Mycobacterium tuberculosis (TB), Vibrio cholerae (cholera), Salmonella typhi (typhoid) |
| Viruses | HIV, influenza, SARS-CoV-2 |
| Fungi | Candida albicans (thrush), Aspergillus (aspergillosis) |
| Protoctista | Plasmodium (malaria), Trypanosoma (sleeping sickness) |
| Type | Definition | Examples |
|---|---|---|
| Communicable (infectious) | Caused by pathogens; can spread from one organism to another | TB, cholera, malaria, influenza, HIV/AIDS |
| Non-communicable | Not caused by pathogens; cannot spread between organisms | Cancer, coronary heart disease, diabetes, asthma |
Pathogens can be transmitted between hosts by several routes:
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