The term 'enzootic' refers to what type of pathogen occurrence?

The term 'enzootic' specifically refers to a pathogen that is continually present in a specific animal population, particularly in non-human vertebrates. This concept is often used in the context of diseases that are consistently maintained in wildlife species, where the infection doesn’t require the introduction of the pathogen from external sources for the disease to be present.

In an enzootic situation, the disease may have a stable and predictable incidence over time within that particular population. This differs fundamentally from sporadic occurrences, where a pathogen may appear infrequently, or from conditions affecting only humans or mammals. Thus, choosing the definition that captures the continuous presence of a pathogen in a non-human vertebrate population accurately describes the nature of an enzootic situation.