Pathogenicity is defined as:

Pathogenicity is defined as:

• A. The severity of disease after infection.
• B. The ability of an organism to cause disease.
• C. The rate of mutation in a pathogen.
• D. The host's immune response to infection.

Answer: (B)

Pathogenicity is the inherent capacity of a microbe to cause disease in a host. It reflects the organism’s ability to enter or adhere to the host, replicate, evade or overcome defenses, and produce tissue damage that leads to illness. This concept focuses on what the microbe is able to do to cause disease, not how severe the disease becomes once it appears. That’s why the other ideas don’t fit as well: the severity of disease describes how bad the illness is (virulence is related but distinct), the rate of mutation is about genetic change in the pathogen, and the host’s immune response is about the host, not the microbe’s inherent ability to cause disease.

Pathogenicity is the inherent capacity of a microbe to cause disease in a host. It reflects the organism’s ability to enter or adhere to the host, replicate, evade or overcome defenses, and produce tissue damage that leads to illness. This concept focuses on what the microbe is able to do to cause disease, not how severe the disease becomes once it appears.

That’s why the other ideas don’t fit as well: the severity of disease describes how bad the illness is (virulence is related but distinct), the rate of mutation is about genetic change in the pathogen, and the host’s immune response is about the host, not the microbe’s inherent ability to cause disease.