The ability of a pathogen to cause a disease.
The state of producing or being able to produce pathological changes and disease.
The quality or characteristic of being pathogenic pertains to the ability to cause disease, and is frequently measured by its degree of virulence. However, it is important to maintain a distinction between pathogenicity and virulence, as recommended by A.A. Miles in a 1955 symposium held by the Society for General Microbiology. Pathogenicity should be considered as an attribute of a genus, species, or other commonly accepted grouping, regardless of the fact that certain entities within the group may not be pathogenic in a given host. Virulence, on the other hand, is the ability of an individual entity in the group to cause disease under specific conditions. The presence of virulence in the group determines whether or not it is deemed pathogenic. Therefore, a non-virulent strain of a pathogenic species may exist.