The above picture shows the stages of infectious disease. Basically, there are five different stages of infectious disease which include the incubation stage, the prodormal stage, the illness stage, the decline stage and the convalescence.
Firstly, the incubation period is a period where there are no signs and symptoms detected while the virus is incubating. It is the time elapsed between exposure to a pathogenic organism, a chemical or radiation, and when symptoms and signs are first apparent.
Secondly, the prodormal period is neither a stage where there are vague and general symptoms, not more nor less.
Thirdly, here comes the illness period. It is a stage which has the most severe signs and symptoms. The illness stage is an interval when patient manifests signs and symptoms specific to type of infection.
Fourthly, the decline period is a time when there is declining signs and symptoms.
And finally, the convalescence stage is a period when there are NO signs and symptoms at all. It is the gradual recovery of health and strength after an illness.