The virulence of a pathogen is defined by the microorganism's _____ and _____。」

• A. Invasiveness and Infectivity
• B. Invasiveness and Toxigenicity
• C. Toxigenicity and Virulence
• D. Infectivity and Virulence

Answer: (B)

Virulence is about how capable a pathogen is at causing disease, which comes from two main abilities: invading tissues and producing toxins. Invasiveness is the power to invade host tissues and spread within the body, leading to widespread damage beyond the initial entry site. Toxigenicity is the capacity to produce toxins that directly harm cells and disrupt normal bodily functions, causing symptoms and organ dysfunction. Together, these two factors largely determine the severity of disease a pathogen can induce. Infectivity, while important for establishing infection, relates to getting into the host rather than how badly the disease will hurt the host once infection is underway. So the combination of invasiveness and toxigenicity best explains virulence.