Which term denotes the ability of a biological agent to enter and grow in the host?

Which term denotes the ability of a biological agent to enter and grow in the host?

• A. Infectivity
• B. Transmission
• C. Pathogenicity
• D. Immunity

Answer: (A)

Infectivity is the capacity of a biological agent to enter a susceptible host and multiply, establishing an infection. It focuses on how readily the agent can begin its life cycle inside the host. This differs from transmission (how the agent spreads between hosts), pathogenicity (the ability to cause disease once infection is established), and immunity (the host’s defenses against infection). An agent can be highly infectious (easy to enter and grow) yet vary in how severely it diseases the host, illustrating that infectivity and virulence are related but distinct concepts.

Infectivity is the capacity of a biological agent to enter a susceptible host and multiply, establishing an infection. It focuses on how readily the agent can begin its life cycle inside the host. This differs from transmission (how the agent spreads between hosts), pathogenicity (the ability to cause disease once infection is established), and immunity (the host’s defenses against infection). An agent can be highly infectious (easy to enter and grow) yet vary in how severely it diseases the host, illustrating that infectivity and virulence are related but distinct concepts.