Final answer:
For an infectious disease to develop, a microorganism must penetrate skin or mucous membranes, survive natural body defenses including the innate immune system, and evade adaptive immune responses. Therefore, the correct answer is 'D. All of the above.'
Step-by-step explanation:
For an infectious disease to develop in a host, a microorganism must first effectively penetrate the skin or mucous membrane, which are part of the body’s initial barriers to infection. These physical barriers, along with chemical defenses like mucus and cilia, help to protect against pathogens. If these barriers are breached, pathogens can enter the body through skin abrasions or punctures, or by overwhelming the protections at mucosal surfaces.
Next, they must survive natural body defense mechanisms such as the innate immune response, which includes inflammation and the engulfment of pathogens by immune cells. Some pathogens have evolved mechanisms to overcome these defenses and remain undetected or resistant to initial immune responses.
Lastly, pathogens must be able to evade or survive adaptive body defense mechanisms, the specialized part of the immune system that develops as it encounters specific pathogens. This adaptive system involves cells that can learn to recognize and target specific invaders, making it a very effective form of pathogen suppression over time.
Therefore, the correct answer to the student's question is D. All of the above.