What is a pathogen?
It is a disease causing microorganism, some examples are some bacteria, some fungi and all viruses.
How do they enter the host?
Pathogens can penetrate an organisms interface with the environment in many ways, three main ways are:
- gas exchange system
- skin, then via blood stream
- digestive system
How do they cause disease?
Once inside the body, they can cause disease in two main ways:
- by producing toxins, eg. Tetanus produces a toxin that blocks certain functions of nerve cells
- cell damage can be done by the pathogens physically damaging the host cells, eg. Rupturing them to release the nutrients (proteins) inside them, breaking down the cells nutrients for its own use, and this eventually starves and destroys the host cell, replicating itself whilst still inside the host cell, then bursting (destroy) the cell when it is released from the inside.