How would one describe an agent with a strong ability to invade the host undetected?

The correct response is associated with the term "High Infectivity." This term refers to an organism's ability to establish an infection in a host, often without triggering immediate or noticeable immune responses. An agent with high infectivity can efficiently enter, survive, and replicate within the host's body, often going undetected in the early stages of infection. This characteristic allows the pathogen to spread more easily from one host to another, as it may not cause significant symptoms initially, allowing for more opportunities for transmission.

In this context, it's important to differentiate infectious agents based on their characteristics. For instance, "Low Virulence" implies a reduced capacity to cause disease, which does not align with the concept of evading detection successfully. "Weak Pathogenicity" also suggests an inability to cause disease effectively, further distancing it from the idea of an agent being capable of invading undetected. Lastly, "High Resistance" generally refers to the ability of a host to defend itself against infections, rather than pertaining to the infective capabilities of the pathogen. Thus, "High Infectivity" accurately describes the agent's propensity to invade a host without raising alarm, making it the most suitable choice.