An infestation is a type of disease caused by parasites, rather than the usual forms of disease, and they require special means to cure and may be contracted by those normally immune to disease, including androids, for instance. Undead creatures, and other non-living creatures, are immune to parasites. Normal magical means of curing diseases are still effective against parasites.
Types of Parasite
Types of Infestation
Different forms of infestation are known and may be found collected in the list of diseases at Diseases of Golarion.