In the usual course (stages) after a pathogen has entered the host body, the stage when the host initially develops the appearance of signs/symptoms like a mild fever and body aches is:

Answer: Prodomal period or stage.

Explanation: The prodromal period comes after after the incubation period (i. e. stage of entry and multiplication).

During this stage, the pathogen continues to multiply and the host starts to establish general signs and symptoms of illness, which occurs as result of the immune system activation. Signs and symptoms like soreness, pain, fever, swelling, or inflammation, is experienced by the host.

However, these signs and symptoms serves as basic diagnostic tool to determine the particular disease.