What are Pathogens?
Pathogens are the organisms which cause disease in living things.
For example., Bacteria, viruses, Fungi, protozoa, helminth, parasites etc.
How parasites cause harm to host ?
Parasites causes harm to the host by living in (or on ) them and multiply in large numbers.
For example, Malaria, a disease caused by parasite.
How pathogen invade host ?
Pathogens enter the body by various places of the body like skin ,mouth, etc and multiply , interfere with normal necessary activities.
It results in morphological & functional damage.
How Pathogens survive in the body of host ?
Pathogens have to adapt to life within the environment of the host.
For example., The pathogens that enter the gut must know a way of surviving in the stomach at low pH (1.5 to 3.5) which is acidic in nature.
And survive in the presence of digestive enzymes.