What characterizes an intermediary host in the context of pathogens?

An intermediary host is best characterized as an organism that harbors a pathogen temporarily. In many life cycles of pathogens, especially parasites, the intermediary host often serves as a necessary step for the pathogen to develop or reproduce before reaching its definitive host, where it can achieve its full life cycle. For example, certain parasites undergo developmental changes within the intermediary host, which are crucial for their ability to infect the definitive host effectively.

This role is distinct from a permanent host, which maintains the parasite over a longer duration, and does not act temporarily in the same way. Additionally, while vectors facilitate transmission of pathogens, they do not necessarily host the pathogens in a manner that supports their development, which fundamentally differentiates their role from that of an intermediary host. Lastly, a host that cannot get infected does not serve any role in the context of pathogen life cycles, particularly as it relates to the spread and development of those pathogens. Therefore, recognizing the intermediary host's function in temporarily harboring pathogens is essential for understanding various infection dynamics and disease transmission processes.