In general, the term "infestation" refers to parasitic diseases caused by animals such as arthropods (i.e. mites, ticks, and lice) and worms, but excluding (except) conditions caused by protozoa, fungi, bacteria, and viruses,  which are called infections.
Infestations can be classified as either external or internal with regards to the parasites' location in relation to the host.
External or ectoparasitic infestation is a condition in which organisms live primarily on the surface of the host (though porocephaliasis can penetrate viscerally) and includes those involving mites, ticks, head lice and bed bugs. 
- " infestation" at Dorland's Medical Dictionary
- "Infestation - Definition and More from the Free Merriam-Webster Dictionary".
- Harvard Medical School; Anthony L. Komaroff (28 December 2004). Harvard Medical School Family Health Guide. Simon & Schuster. pp. 889–. ISBN 978-0-684-86373-3. Retrieved 24 April 2010.
- "Bed Bug Information". 2013-03-04.
- "Bedbugs". Skin Problems & Treatments Health Center. Retrieved 2013-11-20.
- Leland S. Shapiro; Leland Shapiro (2005). Pathology and parasitology for veterinary technicians. Cengage Learning. pp. 111-. ISBN 978-1-4018-3745-7.