What term describes the growth of a parasitic organism within the body?

The correct term that describes the growth of a parasitic organism within the body is "infection." Infections occur when microorganisms such as bacteria, viruses, fungi, or parasites enter the body, multiply, and potentially cause harm to the host. They may lead to various symptoms depending on the type of organism and the body's response to it.

Infections can arise from various sources, including direct contact, contaminated environments, or transmission from other individuals. The development of an infection is about the organism establishing itself and proliferating in the host, leading to a state that can provoke an immune response or other physiological effects.

Other terms, while related to health, do not capture the concept as precisely as "infection." For instance, the notion of "mark infection" is not a standard medical term. "Injury" refers to physical harm to the body that doesn’t necessarily involve the establishment of a parasitic organism. "Allergy" relates to an immune response to a substance (allergen) that is typically harmless, rather than the growth of an organism within the body. In summary, "infection" accurately encapsulates the idea of a parasitic entity multiplying within a host.