Final answer:
The onset of fever can include general signs such as fever, pain, soreness, and inflammation, indicating the body's immune response. Specific symptoms vary by illness, from cold-like symptoms with high fever to flu-like signs and recurring fever in chronic diseases. Infections can present cyclical fever, while infants and older adults may show more severe symptoms like apnea and confusion.
Step-by-step explanation:
The signs & symptoms of the first stage or "onset" of fever can include a range of general and nonspecific indications that the body is beginning to fight an infection. During the prodromal period, which follows the incubation period, the pathogen multiplies, and the host may start to experience symptoms such as fever, pain, soreness, swelling, or inflammation. These are part of the body's immune response and are typically too general to pinpoint a specific disease.
Specifically, initial cold-like symptoms with high fever are common, proceeding to a rash in some illnesses three to five days later. For some chronic diseases, there can be an acute febrile illness with a high fever ranging from 40-41 °C (104-105.8 °F) and flu-like signs. Influenza is often characterized by fever, chills, and body aches, followed by cold symptoms lasting a week or more.
Infectious diseases such as louse- and tickborne relapsing fevers begin with a sudden high fever (39-43 °C [102.2-109.4 °F]), headache, and muscle aches, which can recur in cycles. In the case of early onset disease in infants, symptoms include temperature instability, apnea, bradycardia, hypotension, and irritability. A stiff neck, headache, confusion, and convulsions may accompany fever and muscle aches in older adults.