Final answer:
During the long-lasting stage known as the incubation period, pathogens are multiplying within the host without causing noticeable signs or symptoms of disease.
Step-by-step explanation:
During the stage of the infectious process that could last for years, pathogens replicate, but do not cause manifestations. This is referred to as the incubation period, where the pathogen begins multiplying within the host but is still in insufficient numbers to cause signs and symptoms of disease. This phase can vary in length depending on a variety of factors, including the virulence of the pathogen and the strength of the host's immune defenses. This is also a period where the infected individual might not be aware of the developing disease.