Types of pathogen and how they differ

The types of pathogen that can cause disease include many groups of single-celled microorganisms and larger multicellular parasites. Viruses, bacteria, some yeasts, and protozoan parasites are examples of singlecelled pathogens. Fungi and helminths (parasitic worms) are the major multi-cellular pathogens. These pathogens come from very different parts of the biological kingdom and vary considerably in many aspects. Pathogens differ enormously in their size. They also have very different lifestyles and cause disease in a variety of ways.

Size and lifestyle of pathogens