What are pathogens?

(N/A) wide range of organisms belonging to bacteria,viruses,fungi,protozoans,helminths,etc.,can cause disease in humans.
These disease-causing organisms are called pathogens.
Most parasites are therefore pathogens as they cause harm to the host by living in or on them.
Pathogens can enter the body through various means,multiply,and interfere with normal vital activities,which results in morphological and functional damage.
Pathogens must have the ability to adapt to life within the environment of the host.
For example,pathogens entering the gut must know how to survive in the stomach at low $pH$ and resist various digestive enzymes.