There are six main types of disease causing agents or pathogens: prions, viruses, bacteria, protozoans, fungi, and macroparasites.
These pathogens vary greatly in size and shape, and also in the type of diseases they cause in their host.Pathogens can be microscopic (too small
to be seen with the unaided eye) or macroscopic (can be seen with the unaided eye).
Type of Pathogen
Macro parasites
Definition
Multicellular organisms that
are visible to the naked eye,
also called parasites.
Characteristics
 Metabolically dependent on another
living organism ( the host) for
completion of life cycle
 Parasites are either endoparasites (live in
host) or are ectoparasites (live on host).
- Example: tapeworms and fluke 
endoparasites
And mosquitoes, fleas, ticks, leeches,
mites and lice  suck blood
ectoparasites.
 Eukaryotic cells (cells enclosed with
membrane) with cell walls, organelles
but no chloroplasts.
Examples of Disease
 fleas
 ticks
 tapeworms
 bilharzia worms
 hydatid worms
 liver fluke
 many plant parasites,
e.g. aphids
Virus:
Protozoa:
Fungi: