Which term describes a parasite that invades an organism other than its normal host?

The term that best describes a parasite that invades an organism other than its normal host is "accidental parasite." This describes a situation where the parasite mistakenly infects a host that it does not usually inhabit, typically leading to different outcomes compared to its infestation of the normal host. Accidental parasites may not thrive as well in these atypical hosts, which can affect the life cycle or pathogenic potential of the parasite.

In contrast, the other options outline different types of parasitic relationships. A permanent parasite lives within or on a host for an extended period, depending on its life cycle that requires continual association with that host. A temporary parasite, on the other hand, has a brief interaction with a host, often residing for only short periods before leaving. Lastly, a pathogenic parasite is defined primarily by its ability to cause disease, regardless of whether the host is typical or atypical. Thus, while these definitions may overlap in various ways, "accidental parasite" most accurately captures the essence of a parasite invading a non-normal host.