Infectious agents can enter a host in all of the following ways except which?

Infectious agents typically gain entry into a host through various routes that involve direct exposure to the mucous membranes or broken skin. Healthy, intact areas of the skin serve as a primary barrier against pathogens, thereby preventing their entry into the body.

When the skin is unbroken and healthy, it is effective in protecting the underlying tissues and immune system from infections. In contrast, the other options—like the lining of the nose and mouth, the eyes, and the respiratory and gastrointestinal systems—are known pathways for infectious agents to enter the body. Mucous membranes and moist tissues are more susceptible to infection, facilitating the transmission of pathogens. Hence, the correct answer identifies healthy skin as not being a typical entry point for infectious agents.