Final answer:
The first stage of response to infection after a pathogen enters the host is known as the incubation period. It is followed by the prodromal, acute, decline, and convalescent periods, representing different phases in the progression and recovery from the disease. A) Incubation period
Step-by-step explanation:
The first stage of response to infection is known as the incubation period, which is the time between exposure to the pathogen and the onset of symptoms. During this period, the pathogen begins multiplying within the host. Signs and symptoms of the disease are not yet apparent despite the progression of this early phase of infection. This period can vary significantly in length depending on several factors such as the virulence of the pathogen, the host's immune defenses, and the size of the infecting dose.
Following the incubation period is the prodromal period, characterized by general signs and symptoms of illness as the pathogen continues to multiply. These initial symptoms can include fever, pain, and inflammation but are often not specific enough to identify the disease. The acute phase comes next, with the most pronounced symptoms, followed by the decline phase, during which symptoms lessen as the pathogen numbers decrease. The final stage is the convalescent period, where the patient typically recovers and returns to a normal state of health, although some diseases may cause permanent damage.