These parasites can only survive in a host and therefore go directly from one host to another. This may involve complex life cycles.
Examples are:
- Trichomonas
- Taenia
- Trichinella
These parasites spend only part of their lives as a parasite and another part as free-living organism.
Examples are:
- Fasciola hepatica (Liver fluke (douve))
- Schistosoma
- Ascaris
- Haemonchus
These organisms are normally free living and infect a host only by accident.
Examples:
- some free-living amoeba such as:
- Naegleria
Acanthamoeba
- Fungi such as Candida (vaginal candidosis, athlete foot)