What is the term for the process of infecting or the state of being infected by a pathogen?

The term "infection" refers to the process through which a pathogen, such as bacteria, viruses, or other microorganisms, enters the body and begins to multiply. This can lead to a state where the host shows signs of disease resulting from this invasion. Infections can occur in various forms, including localized infections, which affect a specific part of the body, or systemic infections, where the pathogen spreads throughout the body. The key characteristic of infection is the presence of a pathogen causing physiological changes in the host.

In contrast, "invasion" typically refers to the initial entry of a pathogen into the host's body, but it does not necessarily imply a lasting state of infection, as the pathogen may or may not successfully establish itself. "Infestation" often describes the presence of larger parasites like worms or insects, rather than microscopic pathogens, and "illness" refers to the symptoms and effects experienced by a person rather than the process of being infected. Thus, the correct choice effectively encapsulates the entire concept of both the process and the state of being affected by pathogenic microorganisms.