noun, plural: infestations
(ecology) The state of having a large number of pest organisms thriving in a particular area
Infestation generally refers to the presence of an organism regarded as pest. A pest is a general term for organisms (rats, insects, etc.) which may cause illness or damage or consume food crops and other materials important to humans. An organism that is considered a nuisance to man, most usually having pathogenic properties.
Infestation is also used in parasitology to pertain to ectoparasitism. Ectoparasitism is a form of parasitism wherein the parasite lives outside the body of the host. The parasite is referred to in particular as an ectoparasite. In ectoparasitism, the host-parasite relationship is non-mutual. Many of the endoparasitic relationships do not lead to much harm to the host compared with that in endoparasitism. Nevertheless, there are ectoparasites that serve as carriers of disease. For instance, the mosquito, Aedes aegypti, may carry dengue virus, which can cause dengue. The mosquito is an example of an ectoparasite since it benefits from its host, e.g. human, by feeding on the blood of the latter. Other examples of ectoparasitism are ticks, lice, and leech that feed externally from the skin of their host.