Ability of an organism to induce clinically apparent illness is known as:
Infectivity: It is the ability of an infectious agent to invade and multiply in a host. Pathogenicity: It is the ability of an organism to induce clinically apparent illness. Virulence: It is the propoion of clinical cases resulting in severe clinical disease. Ref: Park, 21st Edition, Page 34.
Infectivity
Pathogenicity
Virulence
Viability