Final answer:
The third period of infectious processes, where specific signs and symptoms are at their peak, is known as the illness period. This is the time when the disease's impact on the body is most severe and follows the prodromal period of general symptoms.
Step-by-step explanation:
The third period of infectious processes characterized by the development of specific signs and symptoms is the illness period. During this phase, the number of pathogens present in the host reaches its peak, and signs and symptoms of the disease are most pronounced. This period follows the prodromal period, during which general signs and symptoms begin to appear, but are not specific enough to indicate a particular disease. After the illness period, comes the period of decline where the number of infectious agents starts to decrease, and symptoms begin to subside. Finally, during the convalescent period, patients typically recover and return to normal functions, although some may suffer permanent damage from the illness.